Question

I have a tab delimited file that looks something like this:

foo 0 4

boo 3 2

blah 4 0

flah 1 1

I am trying to calculate log2 for between the two columns for each row. my problem is with the division by zero
What I have tried is this:

cat file.txt | awk -v OFS='\t' '{print $1, log($3/$2)log(2)}' 

when there is a zero as the denominator, the awk will crash. What I would want to do is some sort of conditional statement that would print an “inf” as the result when the denominator is equal to 0.

I am really not sure how to go about this?
Any help would be appreciated
Thanks

Answer 1

You can implement that as follows (with a few additional tweaks):

awk 'BEGIN{OFS="\t"} {if ($2==0) {print $1, "inf"} else {print $1, log($3/$2)log(2)}} file.txt

Explanation:

• if ($2==0) {print $1, "inf"} else {...} – First check to see if the 2nd field ($2) is zero. If so, print $1 and inf and move on to the next line; otherwise proceed as usual.
• BEGIN{OFS="\t"} – Set OFS inside the awk script; mostly a preference thing.
• ... file.txt – awk can read from files when you specify it as an argument; this saves the use of a cat process. (See UUCA)