duplicated entries of an array in awk

Question

I have a file with 4 columns. When I put these 4 columns into an array using NR as the index, the entries are duplicated somehow. See below for an elaboration of the issue.

The first 5 lines of the file look like this

-bash-4.2$ cat -ve file | head -n 5
chr start end p$
13 59341171 59343427 1.86642E-18$
10 72886545 72888679 1.13636E-09$
16 81900987 81902805 6.79697E-09$
1 46797890 46800143 2.24436E-08$

I assigned each line as an entry of an array indexed by the NR, then the print out of the array looks like this (using the first 5 lines as an example):

-bash-4.2$ awk 'NR<6 {a[NR]=$0; 
>                     for(x in a)
>                     print x, a[x]}' file
1 chr start end p
1 chr start end p
2 13 59341171 59343427 1.86642E-18
1 chr start end p
2 13 59341171 59343427 1.86642E-18
3 10 72886545 72888679 1.13636E-09
4 16 81900987 81902805 6.79697E-09
1 chr start end p
2 13 59341171 59343427 1.86642E-18
3 10 72886545 72888679 1.13636E-09
4 16 81900987 81902805 6.79697E-09
5 1 46797890 46800143 2.24436E-08
1 chr start end p
2 13 59341171 59343427 1.86642E-18
3 10 72886545 72888679 1.13636E-09

I can see that the 5 lines of the file are there, but entries are duplicated a few times. I wonder what the problem is and how to fix it. Thanks in advance.

Answer 1

You're telling it to print the entire array for every line where NR < 6.

If you only want to print the array once, do it after the NR < 6 {} block, in an END block.

For example:

awk 'NR<6 { a[NR] = $0 }; 
     END  { for(x in a) print x, a[x] }' file
1 chr start end p
2 13 59341171 59343427 1.86642E-18
3 10 72886545 72888679 1.13636E-09
4 16 81900987 81902805 6.79697E-09
5 1 46797890 46800143 2.24436E-08