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Old 08-02-2012, 06:47 PM   #1
AHJ
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Registered: Jun 2012
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Delete odd (or even) fields with awk


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
 
Old 08-02-2012, 09:52 PM   #2
grail
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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:
1 0 1
1 0
0 1
0 1 0
0
Please explain further what your requirement is?
 
Old 08-02-2012, 10:33 PM   #3
schneidz
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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
 
Old 08-02-2012, 10:52 PM   #4
AHJ
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Registered: Jun 2012
Posts: 6

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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?
 
Old 08-03-2012, 02:08 AM   #5
grail
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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
 
1 members found this post helpful.
Old 08-03-2012, 04:59 PM   #6
AHJ
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Wonderful, thank you grail
 
  


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