How to number the lines according to a field with awk?

Question

Dear all,

I wonder whether there is a way using awk to number the lines according to a field. For example,

Input

2334 332
2334 546
2334 675
7890 222
7890 134
234  45
.
.
.

Based on the 1st field, I would have the following output

Output

1 2334 332
1 2334 546
1 2334 675
2 7890 222
2 7890 134
3 234  45
.
.
.

I would be grateful for your help.

Cheers,

T

Answer 1

awk 'last != $1 { line = line + 1 } { last = $1; print line, $0 }'