comm.py: find common values
The need to find identical elements within columns of different files is surprisingly common (pun intended).
Thus when you install the
bio package another script called
comm.py is also installed.
It is a tool that prints the common elements from two files.’
If file 1 contains:
A B C
and file 2 contains
A C D
then the command:
comm.py file1 file2
will print the common elements present in the first column of both files:
This is the main usecase of the
comm.py has a number of convenience parameters:
-1will print elements unique to file 1:
-2will print elements unique to file 2:
-3will print the union of elements:
-x 1reads a different column from file 1
-y 1reads a different column from file 2
-ttreats the files as tab delimited rather than CSV
The content for either file may come from standard input. In that case the
- symbol should be used instead of file name.
We could use the UNIX tool called
comm to find common or distinct elements. When used properly
comm allows you to answer a wide variety of interesting questions.
comm properly is no easy task.
comm to work the values must be on a single column and must be sorted. Then instead of telling
comm what we want, we have to tell it what we don’t want (what columns to suppress). That usage is completely backwards of how I like to think.
I don’t usually advocate rewriting UNIX tools, in this case, writing a better
comm makes a lot of sense.
comm.py most operations will be quicker to do, simpler to perform and easier to understand. The primary limitation of
comm is that
comm.py loads all elements into memory.
For most use-cases
comm.py will work exceedingly well.
usage: comm.py [-h] [-1] [-2] [-3] [-t] [-x 1] [-y 1] file1 file2 A better 'comm' command. Prints elements common from columns from two files. positional arguments: file1 input file 1 file2 input file 2 optional arguments: -h, --help show this help message and exit -1, --uniq1 prints elements unique to file 1 -2, --uniq2 prints elements unique to file 2 -3, --union prints elements present in both files -t, --tab tab delimited (default is csv) -x 1, --col1 1 column index for file 1 [default=1] -y 1, --col2 1 column index for file 2 [default=1]