Display the standard deviation of a column of numbers with awk

awk '{sum+=$1; sumsq+=$1*$1} END {print sqrt(sumsq/NR - (sum/NR)**2)}' file.dat

By: kaan
2009-03-24 21:56:40

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What Others Think

I was finding that this was 'blowing up' when processing a large number (1000's) of lat/long positions with an error message about attempting to SQRT a negative number. Apparently the correct way is to do two passes, compute the mean first, sum the difference between value & mean. You can do this with: awk '{sum+=$1; array[NR]=$1} END {for(x=1;x<=NR;x++){sumsq+=((array[x]-(sum/NR))**2);}print sqrt(sumsq/NR)}' file.dat
mungewell · 643 weeks and 4 days ago
can you help me how to edit this command, if I have the values in 2nd column?
siti · 603 weeks and 4 days ago
siti: Just replace all occurrences of $1 with $2 (in either version). Thanks to mungewell for pointing out the overflow problem, and to ashawley for the elegant code.
kaan · 603 weeks and 3 days ago
Can someone help me to modify this code to be able to normalize each value of the column. I guess, after having the mean and the standard deviation, this should be pretty easy. thanks in advance.
anurag_bagaria · 568 weeks and 3 days ago

What do you think?

Any thoughts on this command? Does it work on your machine? Can you do the same thing with only 14 characters?

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