how to merge rows that share unique IDs into a comma separated table

Question

I would like to ask for some hints in how to merge rows that share unique IDs into a comma separated table. Any hints in Perl, sed or awk are greatly appreciated.

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Answer 1

$ cat data.txt 
protein_id go_id
4102    GO:0003676
4125    GO:0003676
4125    GO:0008270
4139    GO:0008270
$ perl -aE'sub a{say"$a\t",join", ",@a if$a;@a=($F[1]);$a=$F[0]}$F[0]eq$a?push@a,$F[1]:a()}{a()' data.txt
protein_id      go_id
4102    GO:0003676
4125    GO:0003676, GO:0008270
4139    GO:0008270