A compilation of all my canonical posts and answers to old questions on Stack Overflow. Topic arrangement mirrors the User Guide.

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Pandas Gotchas

• Don't iterate over a DataFrame!

  • How to iterate over rows in a DataFrame in Pandas?
  • Does pandas iterrows have performance issues?

• Never grow a DataFrame!

  • Creating an empty Pandas DataFrame, then filling it?
  • Add one row to pandas DataFrame

• Good habits to build to avoid that dreaded SettingWithCopyWarning

  • How to deal with SettingWithCopyWarning in Pandas?

• Don't use inplace=True!

  • Understanding inplace=True
  • Pandas - is inplace = True considered harmful or not?

IO tools (text, CSV, HDF5, …)

• How can I effectively load data on Stack Overflow questions using pandas read_clipboard?
• Writing a pandas DataFrame to CSV file
• Import CSV file as a pandas DataFrame
• How do I save multi-indexed pandas dataframes to parquet?

Indexing and selecting data

• How to implement 'in' and 'not in' for Pandas dataframe
• Combine duplicated columns within a DataFrame
• Deleting all columns except a few
• Right way to reverse a pandas DataFrame?

MultiIndex / advanced indexing

• How do I slice or filter MultiIndex DataFrame levels?
• Selecting columns from pandas MultiIndex
• Setting DataFrame column headers to a MultiIndex
• Reorder levels of MultiIndex in a pandas DataFrame

Merge, join, and concatenate

• Pandas Merging 101

  • Merging basics - basic types of joins (read this first)

  • Index-based joins

  • Generalizing to multiple DataFrames

  • Performant Cross join

• Cartesian Product in pandas

Reshaping and pivot tables

• Split (explode) pandas dataframe string entry to separate rows
• Pandas column of lists, create a row for each list element

Working with text data

• Convert Columns to String in Pandas Introduce "string" dtype for pandas >= 1.0.

• Fast punctuation removal with pandas

• How to lowercase a pandas dataframe string column if it has missing values?

• String concatenation of two pandas columns

• Remove unwanted parts from strings in a column

• Select by partial string from a pandas DataFrame

• Get first letter of a string from column

Working with missing data

• How to drop rows of Pandas DataFrame whose value in a certain column is NaN?
• GroupBy columns with NaN (missing) values
• How to check if any value is NaN in a Pandas DataFrame
• Convert pandas.Series from dtype object to float, and errors to nans
• How to replace values with None in Pandas data frame in Python?
• Locate first and last non NaN values in a Pandas DataFrame - a discussion on first_valid_index and last_valid_index

Categorical data

Nullable integer data type

• Pandas: ValueError: cannot convert float NaN to integer

Nullable Boolean Data Type

• Preserve NaN values in pandas boolean comparisons

Visualization

• Compare two DataFrames and output their differences side-by-side
• Pretty Printing a pandas dataframe

Computational tools

Group By: split-apply-combine

• Multiple aggregations of the same column using pandas GroupBy.agg()
• Pandas GroupBy.apply method duplicates first group
• Get statistics for each group (such as count, mean, etc) using pandas GroupBy?
• GroupBy pandas DataFrame and select most common value
• Python Pandas Create New Column with Groupby().Sum()
• How to get number of groups in a groupby object in pandas?

Time series / date functionality

• pandas datetime to unix timestamp seconds

Time deltas

Styling

Options and settings

Performance

• For loops with pandas - When should I care?
• Dynamic Expression Evaluation in pandas using pd.eval()
• When should I (not) want to use pandas apply() in my code?
• Performant cartesian product (CROSS JOIN) with pandas
• What is the performance impact of non-unique indexes in pandas?

Scaling to large datasets

Sparse data structures

• Whats the right way to use a SparseDataFrame in Pandas?

Frequently Asked Questions (FAQ)

• How to iterate over rows in a DataFrame in Pandas?
• What is the difference between Series.replace and Series.str.replace?
• Add column of empty lists to DataFrame
• Change data type of columns in Pandas
• Drop rows containing empty cells from a pandas DataFrame
• How to get rid of “Unnamed: 0” column in a pandas DataFrame?
• Difference between map, applymap and apply methods in Pandas
• Convert list of dictionaries to a pandas DataFrame
• Find the max of two or more columns with pandas
• Sorting by absolute value without changing the data
• How do I convert a pandas column or index to a Numpy array?
• Convert pandas dataframe to NumPy array
• Logical operators for boolean indexing in Pandas
• What is the difference between size and count in pandas?
• 'DataFrame' object has no attribute 'sort'
• Python pandas insert list into a cell
• How to add a suffix (or prefix) to each column name?
• How do I get the row count of a Pandas dataframe?
• Rename a specific column in pandas
• Get list from pandas DataFrame column headers

Cookbook