How to write a for loop to iterate through subjects IDs and their associated reaction times and create histogram

I have a data set of several thousand values.

There are 10 unique subj_indx, 1 through 10. Each one represents an experimental subject. Each subject has a bunch of reaction times, rt.

I want to create a for loop that will go through this dataset and generate a histogram of the reaction time data for each subject.

I don't know where to start other than:

rt=subject_data.rt;

for id = 1:length(subj_idx)%loop for each unique id value

%rtIdx = 1:length(rt)

currentid = rt(rtIdx);

rtIdx = 0;

and I'm not sure even that's correct.

Answer 1

[Paul]

Hi Rania,

Check out the splitapply function and workflow. Example with an array, but I think you can make it work with a table

x = [ones(100,1) rand(100,1);2*ones(100,1) rand(100,1)]; % example data
splitapply(@(x) histogram(axes(figure),x),x(:,2),findgroups(x(:,1)))

If you want to pretty-up the histograms, I think splitapply can be used with a user-defined function just as easily.

[Rania Hanna]

Thank you.

I think I did not explain my question well.

My concern isn't so much creating a histogram, it's creating a for loop to go through the dataset and generate a reaction time for each subject.

[Paul]

"I want to create a for loop that will go through this dataset and generate a histogram of the reaction time data for each subject."

That's exactly what the code in the Answer does. think of x(:,1) as the subj_idx and x(:,2) as the rt. A histogram was created for all of the rt data corresponding to subj_idx == 1 and a second histrogram for subj_idx == 2. Maybe this will clarify with a table as an example?

subj_idx = [ones(100,1);ones(100,1)*2];
rt = rand(200,1);
T = table(subj_idx,rt); % example table
splitapply(@(x) histogram(axes(figure),x),T.rt,findgroups(T.subj_idx))

Here's the same data with nicer plots

splitapply(@(rt,subj_idx) myfunc(rt,subj_idx),T.rt,T.subj_idx,findgroups(T.subj_idx))

function myfunc(rt,subj_idx)
figure;
histogram(rt)
title("RT histogram of subj_idx" + double(unique(subj_idx)));
xlabel('RT')
ylabel('Occurences')
end

[Rania Hanna]

Ah, got it, thank you! This helps a lot and I think I can make it work on my data.