How do I print lines for the first appearance of a unique value in a 2-column file?

Question

I have a small snippet of a file I'm working with:

ENSDARG00000032737    ENSDARP00000120731
ENSDARG00000032737    ENSDARP00000049290
ENSDARG00000061051    ENSDARP00000081062
ENSDARG00000061051     
ENSDARG00000061051    ENSDARP00000129708

I only want to print the first instance of each unique value in the first column and the corresponding value in the second column, so my desired output would be:

ENSDARG00000032737    ENSDARP00000120731
ENSDARG00000061051    ENSDARP00000081062

Is there a simple way to accomplish this with awk or uniq or something similar?

Any help would be appreciated.

Answer 1

POSIX AWK:

m1[$1] == 0 {
   m1[$1] = 1
   print
}

For each line:

1. see if first column exists in the "database"
2. if not, add to "database" and print entire line

Answer 2

$ sort -s -k1,1 -u file
ENSDARG00000032737    ENSDARP00000120731
ENSDARG00000061051    ENSDARP00000081062

This sorts the file based on the first column only. While doing so, it ignores lines whose first column has already been seen.

Most implementations of sort has a non-standard -s option (used in the command above) that guarantees that it will be using a "stable" sorting algorithm. A stable sorting algorithm does not change the ordering of entries that have identical keys (first column in your case).

---

Note however that the longer transcript (which both Ensembl and Havana agrees 100% on) for the ENSDARG00000032737 gene is ENSDART00000049291, which codes for ENSDARP00000049290, not ENSDARP00000120731. But that's not really my business.

Answer 3

This idiomatic solution will work robustly using any awk in any shell on every UNIX box:

$ awk '!seen[$1]++' file
ENSDARG00000032737    ENSDARP00000120731
ENSDARG00000061051    ENSDARP00000081062

Answer 4

Best solutions already provided just posting my try

for i in `awk '{if(!seen[$1]++)print $1}' filename`; do sed -n '/'$i'/{p;q}' filename; done

output

ENSDARG00000032737    ENSDARP00000120731
ENSDARG00000061051    ENSDARP00000081062