CODEWITHSUNDEEP
awk
Derek G
Derek G

Reputation: 21

Count lines up from the bottom when 2nd column goes non-zero

Here is a subset of a file for gnuplot with time in secs from 1/1/2000 and daily rainfall in mm:

        559008000   13.500000    
        559094400   2.4000001    
        559180800  0.60000002    
        559267200   13.800000    
        559353600   6.3000002    
        559440000  0.30000001    
        559526400   0.0000000    
        559612800   0.0000000    
        559699200   0.0000000    
        559785600   0.0000000

I want to find the number of days since it rained (it's 4). First step is to reverse the file:

tac rainfile.txt

Now I'm looking for the first non-zero entry in column 2.

tac rainfile.txt | awk '$2 == "0.0000000" {++count} END {print count}'

gives me the total number of lines with zero, but how do I stop counting when I first hit a non-zero value?

Upvotes: 2

Views: 74

Answers (3)

perreal
perreal

Reputation: 97948

You can grep the lines you want and get the last one via tail:

grep '^ *[0-9]\+  [0-9.]*[1-9][0-9.]*' input | tail -1

this gives:

559440000  0.30000001

to get the line number:

echo $(( $(tac in | grep -n '  [1-9][0-9.]* *$' -m 1 | cut -f1 -d:) - 1))

which gives:

 4

Upvotes: -1

hek2mgl
hek2mgl

Reputation: 157967

I would just use awk, tac is not needed here:

awk '$2>0{d=0;next}{d++}END{print d}' rain.txt

tac needs to loop through the file anyway. Sure, it does not need to compare numbers, but unless rainfile.txt is really huge you shouldn't feel a difference. Otherwise see below...

About your initial solution with tac, just add a next and an exit statement:

tac rain.txt | awk '$2 == "0.0000000"{++count;next}{exit}END{print count}'

Note that awk will process the END block after exit has been called.

Upvotes: 2

RavinderSingh13
RavinderSingh13

Reputation: 133458

Could you please try following and let me know if this helps.

awk '($2==0){count++;next} {count=0} END{print count}'  Input_file

Output will be 4 for same. Explanation will be simple, check if any 2nd field is equal to zero, if yes then increase variable named count's value to 1 and use next to skip all further statements. If this condition doesn't satisfy in any line then it will not come in this block and it will nullify the value of count. Finally when all lines are read in END bock print the variable count which is 4.

Upvotes: 1

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