Select certain column of each file, paste to a new file

Question

I have 20 tab delimited files with the same number of rows. I want to select every 4th column of each file, pasted together to a new file. In the end, the new file will have 20 columns with each column come from 20 different files.

How can I do this with Unix/Linux command(s)?

Input, 20 of this same format.  I want the 4th column denoted here as A1 for file 1:

chr1    1734966 1735009 A1       0       0       0       0       0       1       0
chr1    2074087 2083457 A1       0       1       0       0       0       0       0
chr1    2788495 2788535 A1       0       0       0       0       0       0       0
chr1    2821745 2822495 A1       0       0       0       0       0       1       0
chr1    2821939 2822679 A1       1       0       0       0       0       0       0
...

Output file, with 20 columns, each column coming from one of the 20 files' 4th column:

A1       A2       A3       ...       A20
A1       A2       A3       ...       A20
A1       A2       A3       ...       A20
A1       A2       A3       ...       A20
A1       A2       A3       ...       A20
...

Answer 1

with paste under bash you can do:

paste <(cut -f 4 1.txt) <(cut -f 4 2.txt) .... <(cut -f 4 20.txt)

With a python script and any number of files (python scriptname.py column_nr file1 file2 ... filen):

#! /usr/bin/env python

# invoke with column nr to extract as first parameter followed by
# filenames. The files should all have the same number of rows

import sys

col = int(sys.argv[1])
res = {}

for file_name in sys.argv[2:]:
    for line_nr, line in enumerate(open(file_name)):
        res.setdefault(line_nr, []).append(line.strip().split('\t')[col-1])

for line_nr in sorted(res):
    print '\t'.join(res[line_nr])

Answer 2

The following script does this using awk. I have added for convenience a rownumber, which indicates the number of rows in your files (r). The number of columns you'd like to paste is indicated by c.

directory=/your-directory/
r=4
c=20

for n in $(seq 1 $r); do
echo "$n" >> rownumber.txt
done

for n in $(seq 1 $c); do
awk '{ print $4}' /$directory/file-$n.txt > /$directory/output-$n.txt
done

paste /$directory/rownumber.txt /$directory/output-[1-$c]*.txt > /$directory/newfile.txt