Unix code wanted to change column values

Question

I have a file that looks like this: ``` ID1 ID2 3 ID2 ID3 3 ID4 ID5 3 ID6 ID7 4 ID8 ID9 4 ID8 ID6 4 ``` And I want to change it to: ``` ID1 ID2 1 ID2 ID3 1 ID4 ID5 1 ID6 ID7 2 ID8 ID9 2 ID8 ID6 2 ``` So I want to change all 3's and 4's from the third column to 1's and 2's respectively. What is the most efficient way to do this for a very large file? Many thanks in advance!

Accepted Answer

```
awk '{ $3 -= 2; print }' filename >new_filename 
```

Or, if you really only want to touch 3's and 4's:

```
awk '{ if ( $3 == 3 ) { $3 = 1 } else if ( $3 == 4 ) { $3 = 2 }; print}' filename >new_filename
```

Unix code wanted to change column values

Solution

Problem