awk log2 division/ ratio zero

Question

I have a csv file that looks like this:

ID1              ID2         AVG1     AVG2         
ENSG00000207447 RNU6-2    0.101431  0.163308     
ENSG00000207427 SNORA51   0.096551  0            
ENSG00000201784 SNORD14A  0.068653  0.0320985    
ENSG00000207315 SNORA28   0         0.01936      
ENSG00000207787 MIR98     0         0        

I want to calculate the log2 ratio of AVG1 and AVG2 and print it next to the AVG columns for each line so that it looks like this:

ID1              ID2       AVG1         AVG2       log2Ratio
ENSG00000207447 RNU6-2    0.101431  0.163308     2.0632577007
ENSG00000207427 SNORA51   0.096551  0            inf
ENSG00000201784 SNORD14A  0.068653  0.0320985    7.105015172
ENSG00000207315 SNORA28   0         0.01936      0
ENSG00000207787 MIR98     0         0            inf

I've tried

$ awk 'NF> 2 { ratio =($3/$4)/log(2) ; print $0, ratio }' testlog2.csv > testlog2_2.csv
and
$ awk 'BEGIN{OFS="\t"} {if ($4==0) {print $0, "inf"} else {print $0, ($3/$4)/log(2)}}' testlog2.csv > testlog2_2.csv

but awk keeps crashing whenever the denominator is 0. If you have any suggestions how to get round it, that would be excellent.

Answer 1

Your problem is, you should print the head line separately.

to verify it:

kent$  awk 'BEGIN{print "A"/"B"}'                                                                                                                                           
awk: cmd. line:1: fatal: division by zero attempted

You could change your awk line into:

 awk 'BEGIN{OFS="\t"} NR==1{print;next}{if ($4==0) {print $0, "inf"} else {print $0, ($3/$4)/log(2)}}' file

I didn't change much in your codes, basically copy and paste, just add the NR==1 part.

NOTE

if you run the code, you will see that the output is not same as your expected (example in your question). I hope your logic ($3/$4)/log(2) is correct.

the output with NR==1{...} fix:

ID1              ID2       AVG1      AVG2
ENSG00000207447  RNU6-2    0.101431  0.163308   0.896061
ENSG00000207427  SNORA51   0.096551  0          inf
ENSG00000201784  SNORD14A  0.068653  0.0320985  3.08567
ENSG00000207315  SNORA28   0         0.01936    0
ENSG00000207787  MIR98     0         0          inf