find discontinuity in data using awk

Question

Using awk, how to find out the discontinuity in series of data. I have got data like below.

Example: Input data:

shotline   shot
1001       1001
1001       1002
1001       1003
1001       1005
1001       1006
1001       1009
1002       1001
1002       1003

Data should be:

Missing data points:

1001     1004
1001     1007
1001     1008
1002     1002

Answer 1

Here is a working solution:

cat data | awk '{shotline = $1; if(shotline != last_shotline){last_shotline = shotline; last_shot = 1000;} shot = $2; while(shot != last_shot+1){ last_shot = last_shot+1; print shotline " " last_shot }; last_shot = shot;}'