[SOLVED] Delete odd (or even) fields with awk

AHJ · 08-02-2012, 05:47 PM

Hi,

I have a tab delimited file that has duplicate columns (hundreds):
> cat realfile
1 1 0 0 1 1
1 1 0 0 0 0
0 0 1 1 1 1
0 0 1 1 0 0
0 0 0 0 0 0

I want to produce:
> cat wishfile
1 0 1
1 0 0
0 1 1
0 1 0
0 0 0

I know I could do
awk '{print $1, $3, $5)' realfile > wishfile

But it seems silly. I know there must be a better way, since we can index the columns, but can we use $X as the index instead of the number? Any other command that works is fine too, it doesn't have to be in awk.

Thanks for taking the time to help me

grail · 08-02-2012, 08:52 PM

I am not sure I understand

The first line makes sense if consider only duplicates that are side by side, however the second line is not following the same
process otherwise it would have only 2 numbers on the line. Based on the first line I would expect your output to look like:

Code:

Please explain further what your requirement is?

schneidz · 08-02-2012, 09:33 PM

i think s/he wants to print columns 1 3 5 7 ... (or 2 4 6 8 ...)

i tried this but it is not printing a newline 'tween records:

Code:

awk '{for(x=1;x<=NF;++x)if(x % 2 == 0)print $x}' ahj.txt 
1
0
1
1
0
0
0
1
1
0
1
0
0
0
0
[schneidz@hyper ~]$ awk '{for(x=1;x<=NF;x++)if(x % 2 == 0)print "x = " x " - " $x}' ahj.txt 
x = 2 - 1
x = 4 - 0
x = 6 - 1
x = 2 - 1
x = 4 - 0
x = 6 - 0
x = 2 - 0
x = 4 - 1
x = 6 - 1
x = 2 - 0
x = 4 - 1
x = 6 - 0
x = 2 - 0
x = 4 - 0
x = 6 - 0

AHJ · 08-02-2012, 09:52 PM

Thank you for trying

Yes, I want to print all odd columns. The test files work with just a few columns and the command that states all the columns to be printed by number.

In the meantime I actually found an option in a classic genetics tool that does this, so my immediate problem is solved, but I would still like to know how to do this. Google tells me that because the indices are not stored somewhere we can get them, it's hard to define a range of fields in awk, maybe this is a surprisingly difficult problem for the same reason?

grail · 08-03-2012, 01:08 AM

How about:

Code:

awk '{for(x=1;x<=NF;x++)if(x % 2)printf "%s", $x (x == NF || x == (NF-1)?"\n":" ")}' ahj.txt

Or with ruby:

Code:

ruby -ape '$_="\n";$F.each_index{|x| $_.insert(0, "#{$F[x]} ") if x % 2 == 1}' ahj.txt

AHJ · 08-03-2012, 03:59 PM

Wonderful, thank you grail