How to extract lines with common fields

Question

I have a file like this -

1 2 3
1 4 5
a z 3
a 3 4
a f g
b b g

I want to split it into multiple files (as many as there are groups) each containing those lines that have the same first field.

 1 2 3
 1 4 5

 a z 3
 a 3 4
 a f g

 b b g

How do I do that? I tried uniq --all-repeated=separate -w 32 but it considers complete line and not just first column when finding duplicates.

Answer 1

Something like this:

$ awk '{print > $1}' input

$ cat 1
1 2 3
1 4 5

$ cat a
a z 3
a 3 4
a f g

$ cat b
b b g

Answer 2

Slightly nicer file naming approach:

$ ls
file

$ awk '!($1 in a){a[$1]="file"++i}{print > a[$1]}' file

$ ls
file  file1  file2  file3

$ cat file1
1 2 3
1 4 5

$ cat file2
a z 3
a 3 4
a f g

$ cat file3
b b g