median of column with awk

bash sed awk median
Nick picture Nick · May 29, 2011 · Viewed 28.4k times · Source

How can I use AWK to compute the median of a column of numerical data?

I can think of a simple algorithm but I can't seem to program it:

What I have so far is:

sort | awk 'END{print NR}'

And this gives me the number of elements in the column. I'd like to use this to print a certain row (NR/2). If NR/2 is not an integer, then I round up to the nearest integer and that is the median, otherwise I take the average of (NR/2)+1 and (NR/2)-1.

Answer

maxschlepzig picture maxschlepzig · May 29, 2011

With awk you have to store the values in an array and compute the median at the end, assuming we look at the first column:

sort -n file | awk ' { a[i++]=$1; } END { print a[int(i/2)]; }'

Sure, for real median computation do the rounding as described in the question:

sort -n file | awk ' { a[i++]=$1; }
    END { x=int((i+1)/2); if (x < (i+1)/2) print (a[x-1]+a[x])/2; else print a[x-1]; }'

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