Join two CSV files based on a common field

Sometimes it’s necessary to join two CSV files together using a common field. I wrote a python script a while ago to perform this task using the CSV python library ( The script is run from the command line and takes the input and output CSV files and the numbers of the column to match (starting at 0).

For example to join attributes from inMatchFileName.csv to inRefFileName.csv, by matching the first column you can use:

python inRefFileName.csv \
    inMatchFileName.csv outFileName.csv 0 0

Note this assumes there is only one record for each ID, if there are multiple (as in a relational database) this simple aproach won’t work and actually loading the data into a relational database would be better. My recomendation for this is SQLite, a self-contained database (i.e., stored in a single file and doesn’t require setting up a server), that can be accessed from Python and R.

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