Swap two columns - awk, sed, python, perl

Question

I\'ve got data in a large file (280 columns wide, 7 million lines long!) and I need to swap the first two columns. I think I could do this with some kind of awk for loop, to

Answer 1

You can do this by swapping values of the first two fields:

awk ' { t = $1; $1 = $2; $2 = t; print; } ' input_file

Answer 2

You could do this in Perl:

perl -F\\t -nlae 'print join("\t", @F[1,0,2..$#F])' inputfile

The -F specifies the delimiter. In most shells you need to precede a backslash with another to escape it. On some platforms -F automatically implies -n and -a so they can be dropped.

For your problem you wouldn't need to use -l because the last columns appears last in the output. But if in a different situation, if the last column needs to appear between other columns, the newline character must be removed. The -l switch takes care of this.

The "\t" in join can be changed to anything else to produce a different delimiter in the output.

2..$#F specifies a range from 2 until the last column. As you might have guessed, inside the square brackets, you can put any single column or range of columns in the desired order.

Answer 3

I tried the answer of perreal with cygwin on a windows system with a tab separated file. It didn't work, because the standard separator is space.

If you encounter the same problem, try this instead:

awk -F $'\t' ' { t = $1; $1 = $2; $2 = t; print; } ' OFS=$'\t' input_file

Incoming separator is defined by -F $'\t' and the seperator for output by OFS=$'\t'.

awk -F $'\t' ' { t = $1; $1 = $2; $2 = t; print; } ' OFS=$'\t' input_file > output_file