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I have CSV files that have multiple columns that are sorted. For instance, I might have lines like this:

19980102,,PLXS,10032,Q,A,,,15.12500,15.00000,15.12500,2
19980105,,PLXS,10032,Q,A,,,14.93750,14.75000,14.93750,2
19980106,,PLXS,10032,Q,A,,,14.56250,14.56250,14.87500,2
20111222,,PCP,63830,N,A,,,164.07001,164.09000,164.12000,1
20111223,,PCP,63830,N,A,,,164.53000,164.53000,164.55000,1
20111227,,PCP,63830,N,A,,,165.69000,165.61000,165.64000,1

I would like to divide up the file based on the 3rd column, e.g. put PLXS and PCP entries into their own files called PLXS.csv and PCP.csv. Because the file happens to be pre-sorted, all of the PLXS entries are before the PCP entries and so on.

I generally end up doing things like this in C++ since that's the language I know the best, but in this case, my input CSV file is several gigabytes and too large to load into memory in C++.

Can somebody show how this can be accomplished? Perl/Python/php/bash solutions are all okay, they just need to be able to handle the huge file without excessive memory usage.


Splitting a 7 million row CSV by a specific column, How would I go about splitting a very large (7 million rows) CSV file into several different sheets/files by a specific numerical column. It should split  One of the problems with working with data files containing tens of thousands (or more) rows is that they can become unwieldy, if not impossible, to use with “everyday” desktop tools. When I was Revisiting MPs’ Expenses, the expenses data I downloaded from IPSA (the Independent Parliamentary Standards Authority) came in one large CSV file […]


Here's an old school one liner for you (just replace the >> with > to truncate the output files each run):

awk -F, '{print >> ($3".csv")}' input.csv

Due to popular demand (and an itch I just had), I've also written a version that will duplicate the header lines to all files:

awk -F, 'NR==1 {h=$0; next} {f=$3".csv"} !($3 in p) {p[$3]; print h > f} {print >> f}' input.csv

But you could just start with this and finish with the first awk:

HDR=$(head -1 input.csv); for fn in $(tail -n+2 input.csv | cut -f3 -d, | sort -u); do echo $HDR > $fn.csv; done

Most modern systems have the awk binary included, but if you don't have it, you can find an exe at Gawk for Windows

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An alternative solution would be to load the CSV into a Solr index and then generate the CSV files based on your custom search criteria.

Here's a basic HOWTO:

Create report and upload to server for download

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If the first three columns of your file don't have quoted commas, a simple one-liner is:

cat file | perl -e 'while(<>){@a=split(/,/,$_,4);$key=$a[2];open($f{$key},">$key.csv") unless $f{$key};print {$f{$key}} $_;} for $key (keys %f) {close $f{$key}}'

It doesn't consume much memory (only the associations distinct(3rd_column) --> file-handle are stored) and the rows can come in any order.

If the columns are more complex (contain quoted commas for example) then use Text::CSV.

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Split csv file based on column value, Hello Python experts, I have very large csv file (millions of rows) that I My column is string based and the script was looking for integer, I did  Replace file.csv with your csv file, and "department" with the column heading you want to break up files on. It will write a new csv based on each unique value in the selected column. It will write a new csv based on each unique value in the selected column.


How to split rows and columns in a CSV File, Choose to skip Empty Values or not. Transfer Target columns (one or more according to number of splits) to new or existing columns. Indicate  Open CSV file in Excel. The most usually used method must be opening CSV file directly through Excel. 1. Click File > Open > Browse to select a CSV file from a folder, remember to choose All Files in the drop-down list next to File name box. See screenshot: 2. Click Open, and the CSV file has been opened in the Excel. Tip.


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