How to repeat a sequence of numbers to the end of a column? - perl

Question

I have a data file that needs a new column of identifiers from 1 to 5. The final purpose is to split the data into five separate files with no leftover file (split leaves a leftover file).
Data:
aa
bb
cc
dd
ff
nn
ww
tt
pp
with identifier column:
aa 1
bb 2
cc 3
dd 4
ff 5
nn 1
ww 2
tt 3
pp 4
Not sure if this can be done with seq? Afterwards it will be split with:
awk '$2 == 1 {print $0}'
awk '$2 == 2 {print $0}'
awk '$2 == 3 {print $0}'
awk '$2 == 4 {print $0}'
awk '$2 == 5 {print $0}'

Answer 1

Perl to the rescue:
perl -pe 's/$/" " . $. % 5/e' < input > output
Uses 0 instead of 5.
$. is the line number.
% is the modulo operator.
the /e modifier tells the substitution to evaluate the replacement part as code
i.e. end of line ($) is replaced with a space concatenated (.) with the line number modulo 5.

Answer 2

$ awk '{print $0, ((NR-1)%5)+1}' file
aa 1
bb 2
cc 3
dd 4
ff 5
nn 1
ww 2
tt 3
pp 4
No need for that to create 5 separate files of course. All you need is:
awk '{print > ("file_" ((NR-1)%5)+1)}' file
Looks like you're happy with a perl solution that outputs 1-4 then 0 instead of 1-5 so FYI here's the equivalent in awk:
$ awk '{print $0, NR%5}' file
aa 1
bb 2
cc 3
dd 4
ff 0
nn 1
ww 2
tt 3
pp 4

Answer 3

I am going to offer a Perl solution even though it wasn't tagged because Perl is well suited to solve this problem.
If I understand what you want to do, you have a single file that you want to split into 5 separate files based on the position of a line in the data file:
the first line in the data file goes to file 1
the second line in the data file goes to file 2
the third line in the data file goes to file 3
...
since you already have the lines position in the file, you don't really need the identifier column (though you could pursue that solution if you wanted).
Instead you can open 5 filehandles and simply alternate which handle you write to:
use strict;
use warnings;
my $datafilename = shift #ARGV;
# open filehandles and store them in an array
my #fhs;
foreach my $i ( 0 .. 4 ) {
open my $fh, '>', "${datafilename}_$i"
or die "$!";
$fhs[$i] = $fh;
}
# open the datafile
open my $datafile_fh, '<', $datafilename
or die "$!";
my $row_number = 0;
while ( my $datarow = <$datafile_fh> ) {
print { $fhs[$row_number++ % #fhs] } $datarow;
}
# close resources
foreach my $fh ( #fhs ) {
close $fh;
}