Take the 2-minute tour ×  I have two large-ish CSV files. One
file is just a list of records. The other file is a list of
records, but the first column is the line number of the record
that it modifies in the other file. It doesn't replace the whole
row; It just replaces the value in the row that has the matching
header.  For example:  File 1:   File 2:   The goal is to end up
with one file that looks like this:   The data is, however, much
more complicated than that and could even contain line breaks in
the CSV. Thus, I can't rely on the line number and instead I
have to rely on the record count. (Unless, of course, I
preprocess both files to replace newlines and carriage returns..
which I suppose is possible but less interesting.)  The question
I have is how do I loop through both files and do the proper
replacement without loading either of the entire files into
memory. I believe 100mb+ files loaded into memory is a bad idea,
right?  Also, the records in the resulting file should be in the
same order when