How to subtract a constant number from a column

awk subtraction
Sharat Chandra picture Sharat Chandra · Jul 31, 2010 · Viewed 39.4k times · Source

Is there a way to subtract the smallest value from all the values of a column? I need to subtract the first number in the 1st column from all other numbers in the first column.

I wrote this script, but it's not giving the right result:

$ awk '{$1 = $1 - 1280449530}' file 
1280449530 452
1280449531 2434
1280449531 2681
1280449531 2946
1280449531 1626
1280449532 3217
1280449532 4764
1280449532 4501
1280449532 3372
1280449533 4129
1280449533 6937
1280449533 6423
1280449533 4818
1280449534 4850
1280449534 8980
1280449534 8078
1280449534 6788
1280449535 5587
1280449535 10879
1280449535 9920
1280449535 8146
1280449536 6324
1280449536 12860
1280449536 11612

Answer

Michael Mrozek picture Michael Mrozek · Jul 31, 2010

What you have essentially works, you're just not outputting it. This will output what you want:

awk '{print ($1 - 1280449530) " " $2}' file

You can also be slightly cleverer and not hardcode the shift amount:

awk '{
       if(NR == 1) {
           shift = $1
       }

       print ($1 - shift) " " $2
}' file

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