Adding repeating line numbers

Question

I have a file with about 10k lines. I would like to add the line numbers to the first column, but in a way to repeat the line numbers 1-100. For example,

1 12313
2 3434
.
.
.
100 4233
1 24523
.
.
.
100 4543543
1
.
.
.     
100

How could I do it using grep or awk? I managed to print the line numbers, but without repeating using awk

awk '{ print NR, $1 }' p2.dat > p3.dat

Answer 1

Use the modulo (remainder) operator % on NR. NR % 100 would give 1,2,3...99,0,1,2..., so it needs a bit of tweaking. This should do:

awk '{ print (NR-1) % 100 + 1, $1 }' p2.dat > p3.dat

This, of course is an answer to the original question, not the modified one.

Answer 2

This seems to work with a minimum of looping:

awk '{ printf("%0.0f ",(NR/100.001)+.5) ;print $1 }' p2.dat > p3.dat

Demo, print the first 10 numbers, and in groups of 3 prefix an increment:

seq 10 | awk '{ printf("%0.0f ",(NR/3.001)+.5) ;print $1 }'

Output:

1 1
1 2
1 3
2 4
2 5
2 6
3 7
3 8
3 9
4 10

---

Note: awk rounding shows some binary conversion glitches. The above code uses expressions like (NR/3.001)+.5), when it would be clearer to write (NR/3)+.5) or even (NR*(1/3))+.5). Unfortunately those don't work:

# WRONG: (rounding errors), shows four '2's, etc.
seq 10  | awk '{ printf("%0.0f ",(NR/3)+.5) ;print $1 }' 
1 1
1 2
2 3
2 4
2 5
2 6
3 7
3 8
4 9
4 10