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Tabulo

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Tabulo is a Ruby library for generating plain text tables, also known as “ASCII tables”. It is both highly configurable and very easy to use.

Overview

Quick API:

> puts Tabulo::Table.new(User.all, :id, :first_name, :last_name).pack
+----+------------+-----------+
| id | first_name | last_name |
+----+------------+-----------+
|  1 | John       | Citizen   |
|  2 | Jane       | Doe       |
+----+------------+-----------+

Full API:

table = Tabulo::Table.new(User.all) do |t|
  t.add_column("ID", &:id)
  t.add_column("First name", &:first_name)
  t.add_column("Last name") { |user| user.last_name.upcase }
end

> puts table.pack
+----+------------+-----------+
| ID | First name | Last name |
+----+------------+-----------+
|  1 | John       | CITIZEN   |
|  2 | Jane       | DOE       |
+----+------------+-----------+

Features

  • Presents a DRY API that is column-based, not row-based, meaning header and body rows are automatically in sync
  • Lets you set fixed column widths, then either wrap or truncate the overflow
  • Alternatively, “pack” the table so that columns are auto-sized to their contents, but without overflowing the terminal
  • Cell alignment is configurable, but has helpful content-based defaults (numbers right, strings left)
  • Tabulate any Enumerable: the underlying collection need not be an array
  • Step through your table a row at a time, printing as you go, without waiting for the underlying collection to load. In other words, have a streaming interface for free.
  • Add an optional title to your table
  • The header row can be repeated at arbitrary intervals
  • Newlines within cell content are correctly handled
  • Multibyte Unicode characters are correctly handled
  • Option to preserve whole words when wrapping content
  • Apply colours and other styling to table content and borders, without breaking the table
  • Easily transpose the table, so that rows are swapped with columns
  • Choose from multiple border configurations, including Markdown, “ASCII”, and smoothly joined Unicode border characters

Tabulo has also been ported to Crystal (with some modifications): see Tablo.

Contents

Installation ↑

Add this line to your application’s Gemfile:

gem 'tabulo'

And then execute:

$ bundle

Or install it yourself:

$ gem install tabulo

To use the gem, you need to require it in your source code as follows:

require 'tabulo'

Detailed usage ↑

Creating a table ↑

You instantiate a Tabulo::Table by passing it an underlying Enumerable, being the collection of things that you want to tabulate. Each member of this collection will end up corresponding to a row of the table. The collection can be any Enumerable, for example a Ruby Array, or an ActiveRecord relation:

table = Tabulo::Table.new([1, 2, 5])
other_table = Tabulo::Table.new(User.all)

For the table to be useful, however, it must also contain columns…

Adding columns ↑

Quick API ↑

When the columns correspond to methods on members of the underlying enumerable, you can use the “quick API”, by passing a symbol directly to Tabulo::Table.new for each column. This symbol also provides the column header:

table = Tabulo::Table.new([1, 2, 5], :itself, :even?, :odd?)
> puts table
+--------------+--------------+--------------+
|    itself    |     even?    |     odd?     |
+--------------+--------------+--------------+
|            1 |     false    |     true     |
|            2 |     true     |     false    |
|            5 |     false    |     true     |
+--------------+--------------+--------------+

Full API ↑

Columns can also be added to the table one-by-one using add_column. This “full API” is more verbose, but provides greater configurability:

table = Tabulo::Table.new([1, 2, 5])
table.add_column(:itself)
table.add_column(:even?)
table.add_column(:odd?)

Alternatively, you can pass an initialization block to new:

table = Tabulo::Table.new([1, 2, 5]) do |t|
  t.add_column(:itself)
  t.add_column(:even?)
  t.add_column(:odd?)
end

With the full API, columns can also be initialized using a callable to which each object will be passed to determine the value to be displayed in the table. In this case, the first argument to add_column provides the header text:

table = Tabulo::Table.new([1, 2, 5]) do |t|
  t.add_column("N", &:itself)
  t.add_column("Doubled") { |n| n * 2 }
  t.add_column(:odd?)
end
> puts table
+--------------+--------------+--------------+
|       N      |    Doubled   |     odd?     |
+--------------+--------------+--------------+
|            1 |            2 |     true     |
|            2 |            4 |     false    |
|            5 |           10 |     true     |
+--------------+--------------+--------------+

The add_column method can be passed a single parameter callable, as shown in the above example, with the parameter representing the member of the underyling enumerable; or it can be passed 2-parameter callable, with the second parameter representing the (0-based) index of each row. This can be useful if you want to display a row number in one of the columns:

table = Tabulo::Table.new(["a", "b", "c"]) do |t|
  t.add_column("Row") { |letter, row_index| row_index }
  t.add_column("Value", &:itself)
end
> puts table
+--------------+--------------+
|      Row     |     Value    |
+--------------+--------------+
|            0 | a            |
|            1 | b            |
|            2 | c            |
+--------------+--------------+

Column labels vs headers ↑

The first argument to add_column is the called the label for that column. It serves as the column’s unique identifier: only one column may have a given label per table. (Strings and Symbols are interchangeable for this purpose.) The label also forms the header shown at the top of the column, unless a separate header: argument is explicitly passed:

table.add_column(:itself, header: "N")
table.add_column(:itself2, header: "N", &:itself)  # header need not be unique
# table.add_column(:itself)  # would raise Tabulo::InvalidColumnLabelError, as label must be unique

Positioning columns ↑

By default, each new column is added to the right of all the other columns so far added to the table. However, if you want to insert a new column into some other position, you can use the before option, passing the label of the column to the left of which you want the new column to be added:

table = Tabulo::Table.new([1, 2, 3], :itself, :odd?)
table.add_column(:even?, before: :odd?)
> puts table
+--------------+--------------+--------------+
|    itself    |     even?    |     odd?     |
+--------------+--------------+--------------+
|            1 |     false    |     true     |
|            2 |     true     |     false    |
|            5 |     false    |     true     |
+--------------+--------------+--------------+

Extracting column content from a hash or array ↑

Sometimes the data source for the table may be a collection of hashes or arrays. For example:

data = [
  { english: "hello", portuguese: "bom dia" },
  { english: "goodbye", portuguese: "adeus" },
]

or

data = [
  ["hello", "bom dia"],
  ["goodbye", "adeus"],
]

To tabulate such a collection, simply use the same mechanism as described above, passing a block to the add_column method to tell Tabulo how to extract the data for each column from a row. For example, to tabulate the first example above, you could do something like this:

table = Tabulo::Table.new(data) do |t|
  t.add_column("English") { |h| h[:english] }
  t.add_column("Portuguese") { |h| h[:portuguese] }
end

puts table

For the second example, you could do the following:

table = Tabulo::Table.new(data) do |t|
  t.add_column("English") { |a| a[0] }
  t.add_column("Portuguese") { |a| a[1] }
end

puts table

In both cases, the output will be as follows:

+--------------+--------------+
|    English   |  Portuguese  |
+--------------+--------------+
| hello        | bom dia      |
| goodbye      | adeus        |
+--------------+--------------+

If you have previously used other terminal tabulation libraries, you may be accustomed to being required to place your data into an array of hashes or arrays before you can tabulate them. Tabulo, however, offers an API that is more general and flexible than this; your data source can be any enumerable collection (not just an array), and each item in that collection can be any object (not necessarily an array or a hash). However, as shown above, it is still straightforward to tabulate an array of hashes or arrays, if your data source happens to take that form.

Removing columns ↑

There is also a #remove_column method, for deleting an existing column from a table. Pass it the label of the column you want to remove:

table.remove_column(:even?)

Adding a title ↑

You can give your table a title, using the title option:

table = Tabulo::Table.new([1, 2, 3], :itself, :even?, :odd?, title: "Numbers")
> puts table
+--------------------------------------------+
|                   Numbers                  |
+--------------+--------------+--------------+
|    itself    |     even?    |     odd?     |
+--------------+--------------+--------------+
|            1 |     false    |     true     |
|            2 |     true     |     false    |
|            3 |     false    |     true     |
+--------------+--------------+--------------+

There is a caveat: Using the title option with the :markdown border type will cause the rendered table to cease being valid Markdown, as unfortunately almost no markdown engines support adding a captions (i.e. titles) to tables.

Cell alignment ↑

By default, column header text is center-aligned, while the content of each body cell is aligned according to its data type. Numbers are right-aligned, text is left-aligned, and booleans (false and true) are center-aligned.

This default behaviour can be set at the table level, by passing :center, :left or :right to the align_header or align_body options when initializing the table:

table = Tabulo::Table.new([1, 2], :itself, :even?, align_header: :left, align_body: :right)

The table-level alignment settings can be overridden for individual columns by passing similarly-named options to add_column, e.g.:

table.add_column("Doubled", align_header: :right, align_body: :left) { |n| n * 2 }

If a table title is present, it is center-aligned by default. This can be changed using the align_title option when initializing the table:

table = Tabulo::Table.new([1, 2], :itself, :even?, title: "Numbers", align_title: :left)

Column width, wrapping and truncation ↑

Configuring fixed widths ↑

By default, column width is fixed at 12 characters, plus 1 character of padding on either side. This can be adjusted on a column-by-column basis using the width option of add_column:

table = Tabulo::Table.new([1, 2]) do |t|
  t.add_column(:itself, width: 6)
  t.add_column(:even?, width: 9)
end
> puts table
+--------+-----------+
| itself |   even?   |
+--------+-----------+
|      1 |   false   |
|      2 |    true   |
+--------+-----------+

If you want to set the default column width for all columns of the table to something other than 12, use the column_width option when initializing the table:

table = Tabulo::Table.new([1, 2], :itself, :even?, column_width: 6)
> puts table
+--------+--------+
| itself |  even? |
+--------+--------+
|      1 |  false |
|      2 |  true  |
+--------+--------+

Widths set for individual columns always override the default column width for the table.

Automating column widths ↑

Instead of setting column widths “manually”, you can tell the table to sort out the widths itself, so that each column is just wide enough for its header and contents (plus a character of padding on either side):

table = Tabulo::Table.new(["short", "here is a longer phrase"], :itself, :size)
table.pack
> puts table
+-------------------------+------+
|          itself         | size |
+-------------------------+------+
| short                   |    5 |
| here is a longer phrase |   23 |
+-------------------------+------+

If the table title happens to be too long to for the existing width of the table, pack will also arrange for the table to be widened sufficiently to accommodate it without wrapping:

table = Tabulo::Table.new(["a", "b"], :itself, :size, title: "Here are some letters of the alphabet")
table.pack
> puts table
+---------------------------------------+
| Here are some letters of the alphabet |
+-------------------+-------------------+
|       itself      |        size       |
+-------------------+-------------------+
| a                 |                 1 |
| b                 |                 1 |
+-------------------+-------------------+

The pack method returns the table itself, so you can “pack-and-print” in one go:

puts Tabulo::Table.new(["short", "here is a longer phrase"], :itself, :size).pack

You can manually place an upper limit on the total width of the table when packing:

puts Tabulo::Table.new(["short", "here is a longer phrase"], :itself, :size).pack(max_table_width: 24)
+---------------+------+
|     itself    | size |
+---------------+------+
| short         |    5 |
| here is a lon |   23 |
| ger phrase    |      |
+---------------+------+

Or if you simply call pack with no arguments (or if you explicitly call pack(max_table_width: :auto)), the table width will automatically be capped at the width of your terminal.

If you want the table width not to be capped at all, call pack(max_table_width: nil).

If the table cannot be fit within the width of the terminal, or the specified maximum width, then column widths are reduced as required, with wrapping or truncation then occuring as necessary (see Overflow handling). Under the hood, a character of width is deducted column by column—the widest column being targetted each time—until the table will fit.

To resize only specific columns, pack takes an except: argument, which can be a single column label or an Array of column labels. E.g. pack(except: :id) will exclude the id column from resizing and let it keep its current width. This is useful if you want to prevent the addition of linebreaks in your data. When using this option, other columns might be shrunk more to still make the table fit within the max_table_width.

For even finer-grained control over column and table resizing, see the for the #autosize_columns and #shrink_to methods.

Note that packing the table necessarily involves traversing the entire collection up front as the maximum cell width needs to be calculated for each column. You may not want to do this if the collection is very large.

Note also the effect of pack is to fix the column widths as appropriate to the formatted cell contents given the state of the underlying collection at the point of packing. If the underlying collection changes between that point, and when the table is printed, then the columns will not be resized yet again on printing. This is a consequence of the table always being essentially a “live view” on the underlying collection: formatted contents are never cached within the table itself. There are ways around this, however, if this is not the desired behaviour—see below.

Configuring padding ↑

The single character of padding either side of each column is not counted in the column width. The amount of this extra padding can be configured for the table as a whole, using the column_padding option passed to Table.new—the default value of this option being 1.

Passing a single integer to this option causes the given amount of padding to be applied to each side of each column. For example:

table = Tabulo::Table.new([1, 2, 5], :itself, :even?, :odd?, column_padding: 0)
> puts table.pack
+------+-----+-----+
|itself|even?| odd?|
+------+-----+-----+
|     1|false| true|
|     2| true|false|
|     5|false| true|
+------+-----+-----+

Passing an array of two integers to this option configures the left and right padding for each column, according to the first and second element of the array, respectively. For example:

table = Tabulo::Table.new([1, 2, 5], :itself, :even?, :odd?, column_padding: [0, 2])
> puts table.pack
+--------+-------+-------+
|itself  |even?  | odd?  |
+--------+-------+-------+
|     1  |false  | true  |
|     2  | true  |false  |
|     5  |false  | true  |
+--------+-------+-------+

Note how the padding amount is completely unaffected by the call pack.

Padding can also be configured on a column-by-column basis, using the padding option when calling add_column:

table = Tabulo::Table.new([1, 2, 5], :itself, :even?)
table.add_column(:odd?, padding: 3)
> puts table.pack
+--------+-------+-----------+
| itself | even? |    odd?   |
+--------+-------+-----------+
|      1 | false |    true   |
|      2 |  true |   false   |
|      5 | false |    true   |
+--------+-------+-----------+

This column-level padding setting always overrides any table-level column_padding setting, for the column in question.

Overflow handling ↑

By default, if cell contents exceed their column width, they are wrapped for as many rows as required:

table = Tabulo::Table.new(
  ["hello", "abcdefghijklmnopqrstuvwxyz"],
  :itself, :length
)
> puts table
+--------------+--------------+
|    itself    |    length    |
+--------------+--------------+
| hello        |            5 |
| abcdefghijkl |           26 |
| mnopqrstuvwx |              |
| yz           |              |
+--------------+--------------+

Wrapping behaviour is configured for the table as a whole using the wrap_header_cells_to option for header cells and wrap_body_cells_to for body cells, both of which default to nil, meaning that cells are wrapped to as many rows as required. Passing an Integer limits wrapping to the given number of rows, with content truncated from that point on. The ~ character is appended to the outputted cell content to show that truncation has occurred:

table = Tabulo::Table.new(
  ["hello", "abcdefghijklmnopqrstuvwxyz"],
  :itself, :length,
  wrap_body_cells_to: 1
)
> puts table
+--------------+--------------+
|    itself    |    length    |
+--------------+--------------+
| hello        |            5 |
| abcdefghijkl~|           26 |
+--------------+--------------+

The character used to indicate truncation, which defaults to ~, can be configured using the truncation_indicator option passed to Table.new.

Wrapping at word boundaries ↑

By passing :word to the wrap_preserve option on either table initialization (for all columns), or when calling add_column (for an individual column), whole words can be preserved when wrapping:

sentences = [
  "Words are preserved.",
  "Excessively long words may still be split to fit into the configured column width.",
]
table = Tabulo::Table.new(sentences, :itself, :length, column_width: 10, wrap_preserve: :word)
> puts table
+------------+------------+
|   itself   |   length   |
+------------+------------+
| Words are  |         20 |
| preserved. |            |
| Excessivel |         82 |
| y long     |            |
| words may  |            |
| still be   |            |
| split to   |            |
| fit into   |            |
| the        |            |
| configured |            |
| column     |            |
| width.     |            |
+------------+------------+

When wrapping cell content, Tabulo will never insert hyphens itself, although it will recognize existing hyphens, m-dashes and n-dashes as word boundaries.

The wrap_preserve option defaults to the value :rune, meaning by default it will not respect word boundaries when wrapping (although it will always preserve whole multibyte Unicode characters).

Manual cell wrapping ↑

You can “manually” wrap the content of a title, header or body cell at a particular point, simply by placing a newline character, at that point:

table = Tabulo::Table.new(1..3) do |t|
  t.add_column("The number\nitself", &:itself)
  t.add_column("Even?", &:even?)
  t.add_column("Odd?", &:odd?)
end
> puts table
+--------------+--------------+--------------+
|  The number  |     Even?    |     Odd?     |
|    itself    |              |              |
+--------------+--------------+--------------+
|            1 |     false    |     true     |
|            2 |     true     |     false    |
|            3 |     false    |     true     |
+--------------+--------------+--------------+

Tabulo will treat any of the character combinations "\n", "\r\n" or "\r" equally, as a line break, regardless of the platform it’s currently being run on. This ensures things are formatted as expected if, for example, you are examining content that was produced on another platform from the one you’re running Tabulo on.

Formatting cell values ↑

While the callable passed to add_column determines the underyling, calculated value in each cell of the column, there is a separate concept, of a “formatter”, that determines how that value will be visually displayed. By default, .to_s is called on the underlying cell value to “format” it; however, you can format it differently by passing another callable to the formatter option of add_column:

table = Tabulo::Table.new(1..3) do |t|
  t.add_column("N", &:itself)
  t.add_column("Reciprocal", formatter: -> (n) { "%.2f" % n }) do |n|
    1.0 / n
  end
end
> puts table
+--------------+--------------+
|       N      |  Reciprocal  |
+--------------+--------------+
|            1 |         1.00 |
|            2 |         0.50 |
|            3 |         0.33 |
+--------------+--------------+

Note the numbers in the “Reciprocal” column in this example are still right-aligned, even though the callable passed to formatter returns a String. Default cell alignment is determined by the type of the underlying cell value, not the way it is formatted. This is usually the desired result.

If you want to set the default formatter for all columns of the table to something other than #to_s, use the formatter option when initializing the table:

table = Tabulo::Table.new(1..3, formatter: -> (n) { "%.2f" % n }) do |t|
  t.add_column("N", &:itself)
  t.add_column("Reciprocal") { |n| 1.0 / n }
  t.add_column("Half") { |n| n / 2.0 }
end
> puts table
+--------------+--------------+--------------+
|       N      |  Reciprocal  |     Half     |
+--------------+--------------+--------------+
|         1.00 |         1.00 |         0.50 |
|         2.00 |         0.50 |         1.00 |
|         3.00 |         0.33 |         1.50 |
+--------------+--------------+--------------+

Formatters set for individual columns on calling #add_column always override the default formatter for the table.

The formatter callback also has an alternative, 2-parameter version. If formatter is passed a 2-parameter callable, the second parameter will be given a CellData instance, containing additional information about the cell that may be useful in determining how to format it—see the documentation for details.

Colours and other styling ↑

Styling cell content ↑

In most terminals, if you want to print text that is coloured, or has certain other styles such as underlining, you need to use ANSI escape sequences, either directly, or by means of a library such as Rainbow that uses them internally. Tabulo needs to properly account for escape sequences when performing the width calculations required to render tables. The styler option on the add_column method is intended to facilitate this.

For example, suppose you have a table to which you want to add a column that displays true in green if a given number is even, or else displays false in red. You can achieve this as follows using raw ANSI escape codes:

table.add_column(
  :even?,
  styler: -> (cell_value, s) { cell_value ? "\033[32m#{s}\033[0m" : "\033[31m#{s}\033[0m" }
)

Or, if you are using the rainbow gem for colouring, you could do the following:

require "rainbow"

# ...

table.add_column(
  :even?,
  styler: -> (cell_value, s) { cell_value ? Rainbow(s).green : Rainbow(s).red }
)

The styler option should be passed a callable that takes either 2, 3 or 4 parameters. The first parameter represents the underlying value of the cell (in this case a boolean indicating whether the number is even). The second parameter represents the formatted string value of that cell, i.e. the cell content after any processing by the formatter. The third and fourth parameters are optional, and contain further information about the cell and its contents that may be useful in determining how to style it. See the documentation for details.

If the content of a cell is wrapped over multiple lines, then the styler will be called once per line, so that each line of the cell will have the escape sequence applied to it separately (ensuring the styling doesn’t bleed into neighbouring cells).

If the content of a cell has been truncated, then whatever colours or other styling apply to the cell content will also be applied the truncation indicator character.

Styling column headers ↑

If you want to apply colours or other styling to the content of a column header, as opposed to cells in the table body, use the header_styler option, e.g.:

table.add_column(:even?, header_styler: -> (s) { "\033[32m#{s}\033[0m" })

The header_styler option accepts a 1-, 2- or 3-parameter callable. See the documentation for details.

Styling the table title ↑

To apply colours or other styling to the table title, if present, use the title_styler option when initializing the table. This accepts a single-parameter callable:

table = Tabulo::Table.new(1..5, :itself, :even?, :odd?, title: "Numbers", title_styler: -> (s) { "\033[32m#{s}\033[0m" })

The title_styler option accepts a 1- or 2-parameter callable. See the documentation for details.

Styling borders ↑

Styling can also be applied to borders and dividing lines, using the border_styler option when initializing the table, e.g.:

table = Tabulo::Table.new(1..5, :itself, :even?, :odd?, border_styler: -> (s) { "\033[32m#{s}\033[0m" })

Setting default styles ↑

By default, no styling is applied to the headers or body content of a column unless configured to do so via the header_styler or styler option when calling add_column for that particular column. It is possible to apply styling by default to all columns in a table, however, as the table initializer also accepts both a header_styler and a styler option. For example, if you want all the header text in the table to be green, you could do:

table = Tabulo::Table.new(1..5, :itself, :even?, :odd?, header_styler: -> (s) { "\033[32m#{s}\033[0m" })

Now, all columns in the table will automatically have green header text, unless overridden by another header styler being passed to #add_column.

Repeating headers ↑

By default, headers are only shown once, at the top of the table (header_frequency: :start). If header_frequency is passed nil, headers are not shown at all; or, if passed an Integer N, headers are shown at the top and then repeated every N rows. This can be handy when you’re looking at table that’s taller than your terminal.

E.g.:

table = Tabulo::Table.new(1..10, :itself, :even?, header_frequency: 5)
> puts table
+--------------+--------------+
|    itself    |     even?    |
+--------------+--------------+
|            1 |     false    |
|            2 |     true     |
|            3 |     false    |
|            4 |     true     |
|            5 |     false    |
+--------------+--------------+
|    itself    |     even?    |
+--------------+--------------+
|            6 |     true     |
|            7 |     false    |
|            8 |     true     |
|            9 |     false    |
|           10 |     true     |
+--------------+--------------+

Note that if the table has a title, it will not be repeated; only column headers are repeated.

One can achieve even finer-grained control over printing of headers within the table body by stepping through the table a row at a time (using .each or other methods of Enumerable) and calling the the formatted_header method in combination with horizontal_rule to produce headers at arbitrary points in the output.

Using a Table Enumerator ↑

Because it’s an Enumerable, a Tabulo::Table can also give you an Enumerator, which is useful when you want to step through rows one at a time. In a Rails console, for example, you might do this:

> e = Tabulo::Table.new(User.find_each) do |t|
  t.add_column(:id)
  t.add_column(:email, width: 24)
end.to_enum  # <-- make an Enumerator
...
> puts e.next
+--------------+--------------------------+
|      id      |          email           |
+--------------+--------------------------+
|            1 | jane@example.com         |
=> nil
> puts e.next
|            2 | betty@example.net        |
=> nil

Note the use of .find_each: we can start printing the table without having to load the entire underlying collection. (This is negated if we pack the table, however, since in that case the entire collection must be traversed up front in order for column widths to be calculated.)

Accessing cell values ↑

Each Tabulo::Table is an Enumerable of which each element is a Tabulo::Row. Each Tabulo::Row is itself an Enumerable, of Tabulo::Cell. The Tabulo::Cell#value method will return the underlying value of the cell; while Tabulo::Cell#formatted_content will return its formatted content as a string.

A Tabulo::Row can also be converted to a Hash for keyed access. For example:

table = Tabulo::Table.new(1..3, :itself, :even?, :odd?)

table.each do |row|
  row.each { |cell| puts cell.value } # 1, false, true...2, true, false...3, false, true
  puts row.to_h[:even?].value         # false...true...false
end

The column label (being the first argument that was passed to add_column, converted if necessary to a Symbol), always forms the key for the purposes of this Hash:

table = Tabulo::Table.new(1..3) do |t|
  t.add_column("Number") { |n| n }
  t.add_column(:doubled, header: "Number X 2") { |n| n * 2 }
end

table.each do |row|
  cells = row.to_h
  puts cells[:Number].value  # 1...2...3...
  puts cells[:doubled].value # 2...4...6...
end

Accessing the underlying enumerable ↑

The underlying enumerable for a table can be retrieved by calling the sources getter:

table = Tabulo::Table.new([1, 2, 5], :itself, :even?, :odd?)
> table.sources
=> [1, 2, 5]

There is also a corresponding setter, meaning you can reuse the same table to tabulate a different data set, without having to reconfigure the columns and other options from scratch:

table.sources = [50, 60]
> table.sources
=> [50, 60]

In addition, the element of the underlying enumerable corresponding to a particular row can be accessed by calling the source method on that row:

table.each do |row|
  puts row.source # 50...60...
end

Transposing rows and columns ↑

By default, Tabulo generates a table in which each row corresponds to a record, i.e. an element of the underlying enumerable, and each column to a field. However, there are times when one instead wants each row to represent a field, and each column a record. This is generally the case when there are a small number or records but a large number of fields. To produce such a table, we can first initialize an ordinary table, specifying fields as columns, and then call transpose, which returns a new table in which the rows and columns are swapped:

> puts Tabulo::Table.new(-1..1, :even?, :odd?, :zero?, :pred, :succ, :abs).transpose
+-------+--------------+--------------+--------------+
|       |      -1      |       0      |       1      |
+-------+--------------+--------------+--------------+
| even? |     false    |     true     |     false    |
|  odd? |     true     |     false    |     true     |
| zero? |     false    |     true     |     false    |
|  pred |           -2 |           -1 |            0 |
|  succ |            0 |            1 |            2 |
|   abs |            1 |            0 |            1 |
+-------+--------------+--------------+--------------+

By default, a header row is added to the new table, showing the string value of the element represented in that column. This can be configured, however, along with other aspects of transpose’s behaviour. For details, see the documentation.

Configuring borders ↑

You can configure the kind of border and divider characters that are used when the table is printed. This is done using the border option passed to Table.new. The options are as follows.

:ascii—this is the default; the table is drawn entirely with characters in the ASCII set:

> puts Tabulo::Table.new(1..3, :itself, :even?, :odd?, border: :ascii)
+--------------+--------------+--------------+
|    itself    |     even?    |     odd?     |
+--------------+--------------+--------------+
|            1 |     false    |     true     |
|            2 |     true     |     false    |
|            3 |     false    |     true     |
+--------------+--------------+--------------+

> puts Tabulo::Table.new(1..3, :itself, :even?, :odd?, border: :ascii, title: "Numbers")
+--------------------------------------------+
|                   Numbers                  |
+--------------+--------------+--------------+
|    itself    |     even?    |     odd?     |
+--------------+--------------+--------------+
|            1 |     false    |     true     |
|            2 |     true     |     false    |
|            3 |     false    |     true     |
+--------------+--------------+--------------+

:modern—uses smoothly joined Unicode characters:

> puts Tabulo::Table.new(1..3, :itself, :even?, :odd?, border: :modern)
┌──────────────┬──────────────┬──────────────┐
│    itself    │     even?    │     odd?     │
├──────────────┼──────────────┼──────────────┤
│            1 │     false    │     true     │
│            2 │     true     │     false    │
│            3 │     false    │     true     │
└──────────────┴──────────────┴──────────────┘

> puts Tabulo::Table.new(1..3, :itself, :even?, :odd?, border: :modern, title: "Numbers")
┌────────────────────────────────────────────┐
│                   Numbers                  │
├──────────────┬──────────────┬──────────────┤
│    itself    │     even?    │     odd?     │
├──────────────┼──────────────┼──────────────┤
│            1 │     false    │     true     │
│            2 │     true     │     false    │
│            3 │     false    │     true     │
└──────────────┴──────────────┴──────────────┘

Note: The unicode characters used for the :modern border may not render properly when viewing this documentation on some browsers or devices. This doesn’t reflect any brokenness in tabulo itself.

:markdown—renders a GitHub flavoured Markdown table:

> puts Tabulo::Table.new(1..3, :itself, :even?, :odd?, border: :markdown)
|    itself    |     even?    |     odd?     |
|--------------|--------------|--------------|
|            1 |     false    |     true     |
|            2 |     true     |     false    |
|            3 |     false    |     true     |

> puts Tabulo::Table.new(1..3, :itself, :even?, :odd?, border: :markdown, title: "Numbers")
|                   Numbers                  |
|    itself    |     even?    |     odd?     |
|--------------|--------------|--------------|
|            1 |     false    |     true     |
|            2 |     true     |     false    |
|            3 |     false    |     true     |

However, note that when a table is rendered using the :markdown border type in combination with a (non-nil) title, the result will be invalid Markdown. This is because Markdown engines do not generally support adding a caption (i.e. title) element to tables.

:blank—no border or divider characters are printed:

> puts Tabulo::Table.new(1..3, :itself, :even?, :odd?, border: :blank)
    itself         even?         odd?     
            1      false         true     
            2      true          false    
            3      false         true     


> puts Tabulo::Table.new(1..3, :itself, :even?, :odd?, border: :blank, title: "Numbers")
                  Numbers                 
    itself         even?         odd?     
            1      false         true     
            2      true          false    
            3      false         true

:reduced_ascii—similar to :ascii, but without vertical lines:

> puts Tabulo::Table.new(1..3, :itself, :even?, :odd?, border: :reduced_modern)
-------------- -------------- --------------
    itself          even?          odd?     
-------------- -------------- --------------
            1       false          true     
            2       true           false    
            3       false          true     
-------------- -------------- --------------

> puts Tabulo::Table.new(1..3, :itself, :even?, :odd?, border: :reduced_modern, title: "Numbers")
--------------------------------------------
                   Numbers                  
-------------- -------------- --------------
    itself          even?          odd?     
-------------- -------------- --------------
            1       false          true     
            2       true           false    
            3       false          true     
-------------- -------------- --------------

:reduced_modern—similar to :modern, but without vertical lines:

> puts Tabulo::Table.new(1..3, :itself, :even?, :odd?, border: :reduced_ascii)
────────────── ────────────── ──────────────
    itself          even?          odd?     
────────────── ────────────── ──────────────
            1       false          true     
            2       true           false    
            3       false          true     
────────────── ────────────── ──────────────

> puts Tabulo::Table.new(1..3, :itself, :even?, :odd?, border: :reduced_ascii, title: "Numbers")
────────────────────────────────────────────
                   Numbers                  
────────────── ────────────── ──────────────
    itself          even?          odd?     
────────────── ────────────── ──────────────
            1       false          true     
            2       true           false    
            3       false          true     
────────────── ────────────── ──────────────

Note: The unicode characters used for the :reduced_modern border may not render properly when viewing this documentation on some browsers or devices. This doesn’t reflect any brokenness in tabulo itself.

:classic—reproduces the default behaviour in Tabulo v1; this is like the :ascii option, but without a bottom border:

> puts Tabulo::Table.new(1..3, :itself, :even?, :odd?, border: :classic)
+--------------+--------------+--------------+
|    itself    |     even?    |     odd?     |
+--------------+--------------+--------------+
|            1 |     false    |     true     |
|            2 |     true     |     false    |
|            3 |     false    |     true     |

> puts Tabulo::Table.new(1..3, :itself, :even?, :odd?, border: :classic, title: "Numbers")
+--------------------------------------------+
|                   Numbers                  |
+--------------+--------------+--------------+
|    itself    |     even?    |     odd?     |
+--------------+--------------+--------------+
|            1 |     false    |     true     |
|            2 |     true     |     false    |
|            3 |     false    |     true     |

Note that, by default, none of the border options includes lines drawn between rows in the body of the table. These are configured via a separate option: see below.

Row dividers ↑

To add lines between rows in the table body, use the row_divider_frequency option when initializing the table. The default value for this option is nil, meaning there are no dividing lines between rows. But if this option passed is a positive integer N, then a dividing line is inserted before every Nth row. For example:

> puts Tabulo::Table.new(1..6, :itself, :even?, :odd?, row_divider_frequency: 2)
+--------------+--------------+--------------+
|    itself    |     even?    |     odd?     |
+--------------+--------------+--------------+
|            1 |     false    |     true     |
|            2 |     true     |     false    |
+--------------+--------------+--------------+
|            3 |     false    |     true     |
|            4 |     true     |     false    |
+--------------+--------------+--------------+
|            5 |     false    |     true     |
|            6 |     true     |     false    |
+--------------+--------------+--------------+

If you want a line before every row, pass 1 to row_divider_frequency. For example:

> puts Tabulo::Table.new(1..3, :itself, :even?, :odd?, row_divider_frequency: 1)
+--------------+--------------+--------------+
|    itself    |     even?    |     odd?     |
+--------------+--------------+--------------+
|            1 |     false    |     true     |
+--------------+--------------+--------------+
|            2 |     true     |     false    |
+--------------+--------------+--------------+
|            3 |     false    |     true     |
+--------------+--------------+--------------+

In addition to these options, it is also possible to print horizontal dividers at any chosen point in the table output, by stepping through the table one row at a time and calling the horizontal_rule method as required.

Using a table as a snapshot rather than as a dynamic view ↑

The nature of a Tabulo::Table is that of a dynamic view onto the underlying sources enumerable from which it was initialized (or which was subsequently assigned to its sources attribute). That is, if the contents of the sources enumerable change subsequent to initialization of or assignment to sources, then the table when printed will show the sources as they are at the time of printing, not as they were at the time of initialization or assignment. For example:

arr = [1, 2]
table = Tabulo::Table.new(arr, :itself, :even?, :odd?)
> puts table
+--------------+--------------+--------------+
|    itself    |     even?    |     odd?     |
+--------------+--------------+--------------+
|            1 |     false    |     true     |
|            2 |     true     |     false    |
+--------------+--------------+--------------+

arr << 3
> puts table
+--------------+--------------+--------------+
|    itself    |     even?    |     odd?     |
+--------------+--------------+--------------+
|            1 |     false    |     true     |
|            2 |     true     |     false    |
|            3 |     false    |     true     |
+--------------+--------------+--------------+

In this example, even though no direct mutations have been made to table, the result of calling puts table has changed, in virtue of a mutation on the underyling enumerable arr.

A similar behaviour can be seen when sources is an ActiveRecord query, and there are changes to the relevant database table(s) such that the result of the query changes. This is worth bearing in mind when calling pack on a table, since if the sources enumerable changes between packing and printing, then the column widths calculated by the pack method may no longer be “just right” given the changed sources.

If this is not the desired behaviour, there are ways around this. For example, if dealing with an ActiveRecord relation, you can convert the query to a plain array before initializing the table:

sources = User.all.to_a
table = Tabulo::Table.new(sources, :id, :first_name, :last_name)
table.pack
puts table

Passing an Array rather than the ActiveRecord query directly means that if there are changes to the content of the users database table, these will not be reflected in the rendered content of the Tabulo::Table (unless some of the Tabulo::Table columns are based on callables that perform further database queries when called…).

Note that it is also possible simply to store the string value of a table for later use, rather than the table itself:

rendered_table = Tabulo::Table.new(1..10, :itself, :even?, :odd?).pack.to_s

Comparison with other libraries ↑

There are other libraries for generating plain text tables in Ruby. Popular among these are:

DISCLAIMER: My comments regarding these other libraries are based only on my own, possibly flawed reading of the documentation for, and experimentation with, these libraries at the time of my writing this. Their APIs, features or documentation may well change between when I write this, and when you read it. Please consult the libraries’ own documentation for yourself, rather than relying on these comments.

While these libraries have their strengths, I have personally found that, for the common use case of printing a table on the basis of some underlying enumerable collection (such as an ActiveRecord query result), using these libraries feels more cumbersome than it could be.

For example, suppose we have called User.all from the Rails console, and want to print a table showing the email, first name, last name and ID of each user, with column headings. Also, we want the ID column to be right-aligned, because it’s a number.

In terminal-table, we could achieve this as follows:

rows = User.all.map { |u| [u.email, u.first_name, u.last_name, u.id] }
headings = ["email", "first name", "last name", "id"]
table = Terminal::Table.new(headings: headings, rows: rows)
table.align_column(3, :right)
puts table

The problem here is that there is no single source of knowledge about which columns appear, and in which order. If we want to add another column to the left of “email”, we need to amend the rows array, and the headings array, and the index passed to align_column. We bear the burden of keeping these three in sync. This is not be a big deal for small one-off tables, but for tables that have many columns, or that are constructed dynamically based on user input or other runtime factors determining the columns to be included, this can be a hassle and a source of brittleness.

tty-table has a somewhat different API to terminal-table. It offers both a “row-based” and a “column-based” method of initializing a table. The row-based method is similar to terminal-table’s in that it burdens the developer with syncing the column ordering across multiple code locations. The “column-based” API for tty-table, on the other hand, seems to avoid this problem. One way of using it is like this:

users = User.all
table = TTY::Table.new [
  {
    "email" => users.map(&:email),
    "first name" => users.map(&:first_name),
    "last name" => users.map(&:last_name),
    "id" => users.map(&:id),
  }
]
puts table

While this doesn’t seem too bad, it does mean that the underlying collection (users) has to be traversed multiple times, once for each column, which is inefficient, particularly if the underlying collection is large. In addition, it’s not clear how to pass separate formatting information for each column when initializing in this way. (Perhaps there is a way to do this, but if there is, it doesn’t seem to be documented.) So it seems we still have to use table.align_column(3, :right), which again burdens us with keeping the column index passed to align_column in sync.

As for table_print, this is a handy gem for quickly tabulating ActiveRecord collections from the Rails console. table_print is similar to tabulo in that it has a column-based API, so it doesn’t suffer from the multiple-source-of-knowledge issue in regards to column orderings. However, it lacks certain other useful features, such as the ability to repeat headers every N rows, the automatic alignment of columns based on cell content (numbers right, strings left), and a quick and easy way to automatically resize columns to accommodate cell content without overflowing the terminal. Also, as of the time of writing, table_print’s last significant commit (ignoring a deprecation warning fix in April 2018) was in March 2016.

Finally, it is worth mentioning the hirb library. This is similar to table_print, in that it’s well suited to quickly displaying ActiveRecord collections from the Rails console. However, like table_print, there are certain useful features it’s lacking; and using it outside the console environment seems cumbersome. Moreover, it seems no longer to be maintained. At the time of writing, its last commit was in March 2015.

Contributing ↑

Issues and pull requests are welcome on GitHub at https://github.com/matt-harvey/tabulo.

To start working on Tabulo, git clone and cd into your fork of the repo, then run bin/setup to install dependencies.

bin/console will give you an interactive prompt that will allow you to experiment; and bundle exec rake spec will run the test suite. For a list of other Rake tasks that are available in the development environment, run bundle exec rake -T.

License ↑

The gem is available as open source under the terms of the MIT License.