# How to average a column based on another column?

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Leon on 20 Feb 2014
Commented: Leon on 20 Feb 2014
For example, I have a two column data as below:
1945 23.5
1952 25.6
1952 25.9
1952 23.5
1957 26.7
1957 31.2
How do I get a two column data as below, with the left column being the unique numbers: 1945, 1952, 1957, and the second column being the average values of that year:
1945 23.5
1952 25.0
1957 28.95
I can write a loop to do this, but think it must have an easier way to do this.
Thank you@
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### Accepted Answer

Matt Kindig on 20 Feb 2014
This is a good use of accumarray():
[ud,ix,iy]=unique( data(:,1));
output = [ud, accumarray(iy,data(:,2),[],@mean)];
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Leon on 20 Feb 2014
So cool!
Thank you very much.

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