Replace Column if equal to a specific value

Question

I'm looking to replace the fourth column in a CSV if it equals N/A. I'm trying to change it to -1.
I can't seem to get this to work.

awk -F , '{ if($4 == "N/A") {$4 = -1} }' test.csv

Solution 1

You can use the following awk:

awk -F, '{ $4 = ($4 == "N/A" ? -1 : $4) } 1' OFS=, test.csv

• We set the input and output field separators to , to preserve the delimiters in your csv file
• We check the forth field if it is equal to "N/A" then we assign it the value -1 if not we retain the value as is.
• 1 at the end prints your line with or without modified 4th column depending if our test was successful or not.
• ($4=="N/A"?-1:$4) is a ternary operator that checks if the condition $4=="N/A" is true or not. If true ? then we assign -1 and if false : we keep the field as is.

Test run on sample file:

$ cat file
a,b,c,d,e,f
1,2,3,4,5,6
44,2,1,N/A,4,5
24,sdf,sdf,4,2,254,5
a,f,f,N/A,f,4

$ awk -F, '{ $4 = ($4 == "N/A" ? -1 : $4) } 1' OFS=, file
a,b,c,d,e,f
1,2,3,4,5,6
44,2,1,-1,4,5
24,sdf,sdf,4,2,254,5
a,f,f,-1,f,4

Solution 2

Here is another awk (using example data from jaypal)

awk -F, '$4=="N/A" {$4=-1}1' OFS=, file
a,b,c,d,e,f
1,2,3,4,5,6
44,2,1,-1,4,5
24,sdf,sdf,4,2,254,5
a,f,f,-1,f,4

Comments

[mklement0]

+1 for the great explanation (though it's probably overkill to rebuild every input line by always assigning to $4). Can I suggest putting a space before the final 1 to better indicate that it is a separate command (pattern with implied action)?

[Timo]

ofs is a built in variable and the output field separator, see here

[Timo]

I like the else possibility, +1