created the load_ipums_extract() function, test cases, etc.

src/IPUMS.jl

@@ -59,4 +59,5 @@ module IPUMS
     export IPUMSAPI
     export parse_ddi
     export extract_download
+    export load_ipums_extract
 end

src/parsers/ddi_parser.jl

@@ -46,9 +46,9 @@ function parse_ddi(filepath::String)
     # get variables metadata from file
     _get_var_metadata_from_ddi!(ddi)
 
-    return ddi
+    return ddi;
 
-end
+end;
 
 
 """
@@ -80,6 +80,35 @@ function _check_that_file_is_xml(filepath::String)
 end
 
 
+"""
+    _check_that_file_is_dat(filepath::String)
+
+This is an internal function and checks whether the provided file is a DAT
+    file. All IPUMS extract data files should be in DAT format.
+
+### Arguments
+
+- `filepath::String` - A file path that the user wishes to import. The file must be
+                    a DAT file.
+
+### Returns
+
+The function returns nothing if the file is a DAT file. If the file is not 
+    a DAT file, then the function raises an `ArgumentError`.
+"""
+function _check_that_file_is_dat(filepath::String)
+
+    extension = filepath[findlast(==('.'), filepath)+1:end]
+
+    if extension != "dat"
+        throw(ArgumentError("The IPUMS Extract File: $filepath should be an DAT file."))
+    else
+        return true
+    end
+
+end
+
+
 """
     _check_that_file_exists(filepath::String)
 
@@ -308,3 +337,145 @@ function _string_to_num(x::SubString{String})
     return parse(Int64, n)
 end
 
+
+"""
+    load_ipums_extract(ddi::DDIInfo, extract_filepath::String)
+
+    This file will take in a parsed DDIInfo object and file path to an IPUMS
+    DAT extract file, and returns a dataframe containing all of the data. 
+
+### Arguments
+
+- `ddi::DDIInfo` - A DDIInfo object, which is the result of parsing a DDI metadata file.
+- `extract_filepath::String` - The directory path to an IPUMS extract DAT file. 
+
+### Returns
+
+    This function outputs a Julia Dataframe that contains all of the data from 
+    the IPUMS extract file. Further, the metadata fields of the Dataframe 
+    contain the metadata parsed from the DDI file.  
+
+# Examples
+
+Let's assume we have an extract DDI file named `my_extract.xml`, and an extract
+file called `my_extract.dat`.
+
+```julia-repl
+julia> ddi = parse_ddi("my_extract.xml");
+julia> df = load_ipums_extract(ddi, "my_extract.dat");
+```
+
+"""
+function load_ipums_extract(ddi::DDIInfo, extract_filepath::String)
+
+    # Check that the extract file exists and is a DAT file.
+    _check_that_file_is_dat(extract_filepath)
+    _check_that_file_exists(extract_filepath)
+
+    # Load ddi column-level metadata to local variables
+    name_vec = [v.name for v in ddi.variable_info]
+    range_vec = [v.position_start:v.position_end for v in ddi.variable_info]
+    dtype_vec = [v.var_dtype[] for v in ddi.variable_info]
+    dcml_vec = [v.dcml for v in ddi.variable_info]
+
+    # Create empty dataframe
+
+    df = DataFrame(dtype_vec, name_vec)
+
+    # Save extract level metadata to dataframe. This data applies to the entire
+    # file.
+
+    metadata!(df, "conditions", ddi.conditions, style=:note);
+    metadata!(df, "citation", ddi.citation, style=:note);
+    metadata!(df, "ipums_project", ddi.ipums_project, style=:note);
+    metadata!(df, "extract_notes", ddi.extract_notes, style=:note);
+    metadata!(df, "extract_date", ddi.extract_date, style=:note);
+
+    # Setup and write column level metadata to dataframe.
+    fields = Dict("label" => :labl, 
+                    "description" => :desc, 
+                    "data type" => :var_dtype,
+                    "numeric type" => :var_interval,
+                    "coding instructions" => :coder_instructions,
+                    "category labels" => :category_labels)
+
+    # Iterate over each column in the dataset and save the corresponding metadata 
+    # dictionary for that column to the dataframe.
+    for i in eachindex(ddi.variable_info)
+        for (k,v) in fields
+            colmetadata!(df, 
+                            ddi.variable_info[i].name, 
+                            k, 
+                            getfield(ddi.variable_info[i], v), 
+                            style=:note);
+        end
+    end
+
+    # Load extract data to the dataframe. The original ipums extract is a 
+    # fixed width file with no delimiters. The original file saves float-valued 
+    # variables as integers, hence we must to parse the file to correctly 
+    # extract the float values from corresponding integers. 
+    for line in eachline(extract_filepath)
+        data = map((x,p,d) -> _parse_data(x, p, d), 
+                        [strip(line[r]) for r in range_vec], 
+                        [eltype(a) for a in dtype_vec],
+                        [d for d in dcml_vec])
+        push!(df, data)
+    end
+
+    return df;
+end;
+
+
+"""
+    _parse_census_numbers_to_float(strnum::SubString{String}, decimals::Int64)
+
+    This is an internal function, not for public use. The fixed width format
+    of the IPUMS DAT files encodes all numbers as integers. For example, a 
+    number like 1015.45 is encoded as "10545". This function parses string
+    valued number into a floating point number, given the specified number of 
+    decimals.  
+
+### Arguments
+
+- `strnum::SubString{String}` - A number that is coded as a string.
+- `decimals::Int64` - An integer that indicates the number of decimal place in a floating point number.
+
+### Returns
+
+This function returns the numeric part of the string, coded as an Float64 datatype.
+
+"""
+function _parse_census_numbers_to_float(strnum::SubString{String}, decimals::Int64)
+    return parse(Float64, chop(strnum, tail=decimals) * "." * last(strnum, decimals))
+end
+
+
+"""
+    _parse_data(strnum::SubString{String}, dtype::DataType, decimals::Int64)
+
+    This is an internal function to support the parsing of the fixed width 
+    format of the IPUMS datafile. The file contains only numbers and absolutely
+    no text. This function determines--based upon DDI metadata--whether a 
+    specific text input is designated as an integer or floating point number,
+    and then parses that value accordingly.
+
+### Arguments
+
+- `strnum::SubString{String}` - A string that may contain some numeric data encoded as text.
+- `dtype::DataType` - The datatype that should be applied in the parsing of string number.
+- `decimals::Int64` - The number of decimal values to include in a floating point number.
+### Returns
+
+This function returns the parsed number--integer or float--that corresponds to the input string.
+
+"""
+function _parse_data(strnum::SubString{String}, dtype::DataType, decimals::Int64)
+    if dtype == Float64
+        return _parse_census_numbers_to_float(strnum, decimals)
+    elseif dtype == Int64
+        return parse(dtype, strnum)
+    else 
+        return strnum
+    end
+end

test/runtests.jl

@@ -11,10 +11,14 @@ end
 
 @testset "DDI Parser" begin
     ddi = parse_ddi("testdata/cps_00157.xml")
+    datafile = "testdata/cps_00157.dat"
+    df = load_ipums_extract(ddi, datafile)
     @test ddi.extract_date == "2023-07-10"
     @test ddi.variable_info[1].position_end == 4
     @test ddi._ns == "ddi:codebook:2_5"
     @test size(ddi.data_summary) == (8,6)
     @test_throws ArgumentError parse_ddi("testdata/cps_00157.dat.gz")
     @test_throws ArgumentError parse_ddi("testdata/cps_00156.xml")
+    @test isa(metadata(df), Dict)
+    @test isa(colmetadata(df, :YEAR), Dict)
 end