Good morning,
Novice scripter in Unix here, and I've run into and sed task I can't quite wrap my head around. I'm pulling my hair out fast enough as it is and thought I would go to the knowledge bank.

I have a sorted file that I'm trying to trim down by deleting any line whose first few characters are repeats of a previous line.
i.e.

1 ABCD
1 CDEF
1 EFGH
2 ACDE
2 GLKGI
2 KLIGH
.
.
.
10 ABSD
10 OIHIHN
10 OHOIN
.
.
.
XX LIHIN
XX OIHNM
XX OHINK

I need to delete any line for which the line header (first three charachters are a repeat.) So for the previous lines it would keep the first line that begins with "1 " the first line that begins with "2 " etc. So the end result of the would be

1 ABCD
2 ACDE
.
10 ABSD
.
XX LIHIN

The first three characters are always whole numbers, no more than 2 digits, and followed by a space, but the maximum number changes (it could anywhere between 11 and 40)

I suppose the other option would be to print out the first line that contains "1 ', the first line that contains "2 " etc. and drop them into a new file.
I'm more familiar with SED, but using AWK or something else would be fine too.

Thanks in advance!

This finds the first occurrence of the first field and prints the line. Assuming I got what you want.

Worked like a dream!
It's much appreciated!!