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How to use ranksum with splitapply?

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Filipa Torrao
Filipa Torrao on 20 Oct 2019
Answered: Asvin Kumar on 29 Oct 2019
Hi everybody!
I just started with Matllab last week. I am trying to use the ranksum function with splitapply in order to get the p-value for my 2 different groups, but it is not working. Basically I have an excel file where the first column has a set of on/off parameters and on the 18th column I have the values I want to analyse. I want to get the p-value between on and off values (see below)
Column 1 Column 18
ON 4.3
OFF 7.2
OFF 5.6
ON 8.9
OFF 3.7
(etc) (etc)
I want to get the p-value between datasets [4.3, 8.9] and [7.2 , 5.6 , 3.7], any idea on how to do this?
Thanks in advance!
[num,text,raw]=xlsread('d1_m2_filipa.xlsx');
i=text(:,1);
o=[1:length(y)];
w=[2:length(i)];
k=text(w,1);
y=num(:,18);
grpNums=findgroups(k);
q=splitapply(@mean,y,grpNums);
err=splitapply(@std,y,grpNums);
d=splitapply(@jbtest,y,grpNums);
e=0;
if d==0
e=splitapply(@ranksum,y,grpNums)
else e=0
end

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Answers (1)

Asvin Kumar
Asvin Kumar on 29 Oct 2019
The splitapply function applies the function mentioned as an argument to each group. For the ranksum function we would need to provide two sets of data. We can provide these by partitioning the data using findgroups.
You can use the following code for reference and adapt it to your use case:
[grpNums, grps] = findgroups(k);
off = y(k==grps(1));
on = y(k==grps(2));
[p,h] = ranksum(on,off);
Here’s the documentation of findgroups for reference:

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