# How to use prctile in grpstats?

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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.

Tom Lane on 16 May 2013
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]))
Lei on 16 May 2013
I see. Thx!