Asked by Lei
on 15 May 2013

Hello, I am using the grpstats function to get some statistic based on groups; however, I have trouble to use prctile for the whichstats. As the prctile requires a both input X and p. The p I want is [ 5 95]. But for the input x, I don't know how to handle with this as I have predefined X in the grpstats. Here is my grpstats input example:

[A,B,C,D,E,F] = grpstats(sample(:,2),sample(:,7),{'gname','numel','mean','var','skewness',@iqr});

Sample(:,2) is my input data, and sample(:,7) is the group. **I am wondering how can I use the prctile in the grpstats properly**.
Thanks.

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Answer by Tom Lane
on 16 May 2013

Accepted answer

The trick is to use an anonymous function that has the desired percentiles built in. For example, the following two calls to grpstats yield the same results:

x = randn(1000,2); g = randi(5,1000,1); grpstats(x,g, @median) grpstats(x,g, @(x) prctile(x,50))

The following yields a 3-D array where the middle page, a(:,:,2), has the median and the other pages have the 5% and 90% points:

a = grpstats(x,g, @(x) prctile(x,[5 50 90]))

Tom Lane
on 16 May 2013

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