An ipumsr Workflow for Big CenSoc Data

Downloading 1940 Full-Count Census from IPUMS

Once you have an account, visit https://usa.ipums.org/usa/ to make a data extract. Select ‘GET DATA’, listed under ‘CREATE YOUR CUSTOM DATA SET.’

Merging CenSoc and Census Data

To work with the full CenSoc files, you’ll first need to (i) read in the 1940 census, (ii) read in the CenSoc File, and (iii) merge them on the HISTID variable. Note that we also have pre-linked CenSoc “demo” files — please see this vignette for more information.

One challenge of working with the full CenSoc files is that you must work with large files. For example:

• Full Count 1940 Census File (30 variables): 132 million records, 18 GB
• CenSoc Numident: 6.8 million records, 760 MB

If both datasets fit into your computer or server’s memory, merging the datasets on the HISTID variable is straightforward.

## Library Packages
library(tidyverse) ## functions for data manipulation and visualization
library(ipumsr) ## reads in IPUMS data and associated metadata

## read in censoc file
censoc <- read_csv("/path/to/censoc/censoc_numident_v1.csv")

## read in census file with ipumsr package
census <- read_ipums_micro(data_file = '/path/to/ipums/usa_00036.csv.gz',
                           ddi = '/path/to/ipums/usa_00036.xml')

## join the census files by HISTID
censoc_numident_linked <- inner_join(censoc, census, by = "HISTID")

“Chunked” strategy for overcoming memory limitations

A memory-conscious solution is to break the census dataset up and work in chunks. The ipumsr package has the read_ipums_micro_chunked() functions to read in a set number of observations at a time (chunks). The code below uses that function to (i) read in a chunk of the 1940 census (ii) merge that chunk to the CenSoc file on the HISTID variable and (iii) repeat for every chunk and then combine all the merged chunks. Then you’ll be ready to get started on your analysis.

Depending on how many variables you’ve included in your 1940 census extract, the approach may take a while. For reference, the below code took approximately 50 minutes on a 2018 Macbook Pro with 16GB of installed memory (RAM). The good news is that you only need to do this once — see the instructions below on how to save your merged data file.

Note: This approach requires 10GB+ of available RAM.

## Set paths to censoc file 
censoc <- read_csv("/path/to/censoc/censoc_numident_v1.csv")

## Set paths to IPUMS data file — .csv or .dat file! 
ipums_data <- '/path/to/census/usa_00033.csv'

## Set path to IPUMS DDI file 
ipums_ddi <- '/path/to/census/ddi/usa_00033.xml'

## Read in data in chunks and merge with censoc
censoc_numident_linked <- read_ipums_micro_chunked(ddi = ipums_ddi,
                                           data_file = ipums_data, 
  callback = IpumsDataFrameCallback$new(function(x, pos) {
    inner_join(x, censoc, by = "HISTID")
  }), 
  chunk_size = 500000,
)

#> Use of data from IPUMS USA is subject to conditions including that users should
#> cite the data appropriately. Use command `ipums_conditions()` for more details.

#> |========================================================   | 90% 16963 MB

There are a few other strategies for handling datasets too large for memory in R:

• Three Strategies for Working with Big Data in R. (link)
• Big IPUMS Data vignette (link)
• Introduction to Disk.Frame package (link)

Assign metadata to already-linked CenSoc data

If you import and link your CenSoc file to the 1940 Census using a different approach, you can still use the IPUMSR package to assign meaningful value labels to the linked file — just use the ipums_collect() function.

## read in IPUMS DDI for IPUMS extract
ddi_extract <- read_ipums_ddi("/path/to/ddi/usa_00033.xml")

## assign metadata using the ipumsr package
censoc_numident_linked <- ipums_collect(data = censoc_numident_linked,  
                       ddi = ddi_extract, 
                       var_attrs = c("val_labels", "var_label", "var_desc"))

Explore variable descriptions

The ipums_view() function will display a webpage with variable descriptions and value labels in the RStudio viewer. This is an easy way to learn more about the 1940 census variables.

ipums_view(censoc_numident_linked)

Set Value Labels

The ipumsr package imports the associated metadata, such as variable labels, value labels, and more from the IPUMS extract. Particularly helpful are value labels, which translate the numeric IPUMS code into meaningful text strings (e.g., the SEX variable has value labels: 1 = “Male”, 2 = “Female.”)

The ipumsr package stores labelled values using the labelled class from the haven package. The main way to create a factor variable from these labels is the as_factor() function (note: the base R as.factor() function will not work).

For example, if you’re interested in birthplace, you can convert the numeric BPL into a meaningful text string variable using the as_factor() function:

## Look at value labels for birthplace 
ipums_val_labels(censoc_numident_linked$BPL)

## A tibble: 163 x 2
#     val lbl                 
#   <dbl> <chr>               
# 1     1 Alabama             
# 2     2 Alaska              
# 3     4 Arizona             
# 4     5 Arkansas            
# 5     6 California          
# 6     8 Colorado   

## create a new string variable for birthplace 
censoc_numident_linked$BPL_string = as_factor(censoc_numident_linked$BPL)

## alternative method to create new string variable for birth place (style of tidyverse)
censoc_numident_linked <- censoc_numident_linked %>% 
  mutate(BPL_string = as_factor(BPL))

## look at a few rows
censoc_numident_linked %>%
  select(HISTID, BPL, BPL_string) %>% ## print out a few rows
  sample_n(5) 

We now can use the easily interpretable BPL_string variable for our analysis.

In some cases, it may be useful to keep the original numeric codes. For example, if you want to restrict to persons born in North America, it’s easier to do so with the original BPL codes, as the codes are ordered in a meaningful way—you just restrict to BPL codes below 200. It’s more difficult, however, if you have to specify each individual state and country in North America.

Saving your data and metadata

To save your data file and it’s associated metadata, you need to write it out as an object. The metadata cannot be stored in a .CSV file, so if you want to save the metadata, you’ll need to save the entire object to a file using the saveRDS function.

## save censoc data file with metadata
saveRDS(object = censoc_numident_linked, file = "/path/to/data/censoc_numident_linked.rds")

## read in censoc data file with metadata
censoc_numident_linked <- readRDS("/path/to/data/censoc_numident_linked.rds")

Note: Another option is to convert all the relevant variables from numeric to meaningful factor variables at the beginning of your analysis, and then write out the .CSV file. You’ll lose the metadata, but you can always reassign it with the ipums_collect() function.