Shell Programming and Scripting

Hello, I am having a trouble with awk attempting to reformat a two columns file , such as below:

201 84
201 370
201 544
201 600
213 99
213 250
213 431
220 65
220 129
220 338
220 408
220 501
220 550
231 101
231 350

What I need to do is is to add a third column containing a numeric value (a sort of flag) that increments by a value of 1 (one) as the first column value changes (the value of the first column itself is irrelevant, the important thing is to track when the value changes..). The output should be something like this:

201 84 1
201 370 1
201 544 1
201 600 1
213 99 2
213 250 2
213 431 2
220 65 3
220 129 3
220 338 3
220 408 3
220 501 3
220 550 3
231 101 4
231 350 4


I have tried with the arithmetic and incremental operators but I did not get good results. I will deeply appreciate any help

Thanks!

Do you have to use awk? Something like this works just as well:

Code:

#!/usr/bin/bash

changenumber=0
prevcol=""
while read col1 col2; do if [ "$prevcol" != "$col1" ]; then 
   prevcol=$col1
   changenumber=$(($changenumber+1))
fi
echo $col1 $col2 $changenumber
done < /path/to/file

Code:

awk 'BEGIN{ prev = -1}{ if ( prev != $1 ) { cnt++; prev=$1 } $3=cnt; print }' filename

In awk:

Code:

awk '{if ($1 != tmp ){tmp=$1;c++};print $0,c}' file

Regards

Thanks for the input blowtorch and matrixmadhan..
The awk script worked pretty straightforward! I really appreciate your input, I am sure that I could not have done it without this serious help!