Splitting text file based on column value in unix

Question

I have a text file:

head train_test_split.txt 
1 0
2 1
3 0
4 1
5 1

What I want to do is save the first column values for which second column value is 1 to file train.txt.

So, the corresponding first column value for second column value with 1 are: 2,4,5. So, in my train.txt file i want:

2
4
5

How can I do this easily unix?

janos · Accepted Answer · 2017-05-13 17:53:47Z

5

You can use awk for this:

awk '$2 == 1 { print $1 }' inputfile

That is, $2 == 1 is a filter, matching lines where the 2nd column is 1, and print $1 means to print the first column.

answered May 13, 2017 at 17:53

janos

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2 Comments

Or just the 'truthiness' of $2 will work: awk '$2{print $1}'

@dawg for the given sample yes, but it was not specified that the 2nd column will only have 0 and 1 values.

dawg · Accepted Answer · 2017-05-13 23:28:33Z

1

In Perl:

$ perl -lane 'print "$F[0]" if $F[1]==1' file

Or GNU grep:

$ grep -oP '^(\S+)(?=[ \t]+1$)' file

But awk is the best. Use awk...

answered May 13, 2017 at 23:22

dawg

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the grep one can be simplified to grep -oP '^\S+(?=\h+1$)'