Hi,

I've got what is probably quite an easy little (presumably) awk problem that I just can't seem to work out (mental block...I've already spent ages getting the data into this format!). I want to work out the difference between rows for certain columns. for example:

1359142876 RED 14 BLUE 3 GREEN 71 BLACK 65 
1359135610 RED 13 BLUE 3 GREEN 71 BLACK 65
1359128178 RED 10 BLUE 3 GREEN 68 BLACK 60 
1359121257 RED 8 BLUE 3 GREEN 66 BLACK 52 
ETC

1359142876 RED 14 BLUE 3 GREEN 71 BLACK 65 
1359135610 RED 1 BLUE 0 GREEN 0 BLACK 0
1359128178 RED 3 BLUE 0 GREEN 3 BLACK 5 
1359121257 RED 2 BLUE 0 GREEN 2 BLACK 8 
ETC

Here is for fixed number of columns:

awk 'NR==1 {
 f3=$3;f5=$5;f7=$7;f9=$9;
 print
}NR!=1 {
 t3=$3;t5=$5;t7=$7;t9=$9;
 $3=f3-$3;$5=f5-$5;$7=f7-$7;$9=f9-$9;
 f3=t3;f5=t5;f7=t7;f9=t9;
 print
}' file

awk 'NR==1 {
 for(i=3;i<=NF;i+=2) {
  a[i]=$i;
 }
 print
}NR!=1 {
 for(j=3;j<=NF;j+=2) {
  t[j]=$j;
  $j=a[j]-$j;
  a[j]=t[j];
 }
 print
}' file

awk '{for(f=3; f<=NF;f+=2){
        if(NR==1)A[f]=$f;else{B[f]=A[f]-$f;A[f]=$f; $f=B[f]}
}}1' file

Brilliant, both work a treat, thank you!

And I _think_ I follow what is going on, bonus!