MATLAB: Grouping sessions by participant number

grouping variablesplotting

Hi there,

I have a 84×1 vector which contains 84 unique session numbers for an experiment. Each session is associated with a specific participant. Each session contains 4 blocks of 50 trials. I have a 8×1 vector of unique participant numbers. Each participant should complete 12 sessions (with the exception of a few who didn't complete the full experiment).

My question is, how do I associate specific session numbers with specific subject numbers so that I can plot a single subject's distribution of responses per each individual session?

Thank you in advance for any help.

Best Answer

Why can't you just make up a 2-D array with 84 rows and 202 columns. First column is the session number, second column is the participant ID number, and columns 2 - 202 are the 200 numbers in 4 blocks of 50. I.e, cols 3 - 52 contain block 1, cols 52 - 102 are block 2, cols 103 - 152 are block 3, and the last 50 columns are block 4.

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MATLAB: How to reshape matrix

Your goal isn't clear (see comment under your question). But I think I understand what you're looking for.

Here I make the following assumptions

You have a variable that identifies the subject for each row of your data.
The rows of your 2340x5 matrix is organized by subject. So, the first 90 rows are s1, then 90 rows of s2, etc.
The number of variables (in your case, 90) will always be even. If this is untrue, you'll have to use a cell array rather than a matrix and the two columns will be uneven.
You want to extract data from 1 column at a time. ( This one was really unclear but since you want two columns in a matrix, this has to be the case).

If this is correct, you are not resizing the matrix (ie, using resize()), you are extracting a subset of data to create a new, smaller matrix.

Here I create fake data that fit your description and in 3 lines, I build the 2-column matrix extracting data from column 3 of your data.

% create fake data
nSubj = 26;                          %number of subjects
nVars = 90;                          %number of variables
data = rand(nSubj * nVars, 5);       %your data (fake)
subjID = meshgrid(1:nSubj, 1:nVars); 
subjID = subjID(:);                  %identifies the subject # for each row of data
% create index that chooses rows from first 1/2 of each subject
firstHalfIdx = repmat([true,false], floor(nVars/2), 1); %floor() in case nVars isn't even.
firstHalfIdx = repmat(firstHalfIdx(:), nSubj, 1); 
% Put data into new matrix 
col = 3;     %choose column to extract
dataHalves = [data(firstHalfIdx, col), data(~firstHalfIdx, col)];

dataHalves is a [1170-by-2] matrix where column 1 is the first half of data from all subjects and column 2 is the 2nd half - extracting data from column 3 of your data.

MATLAB: Display the ID of the participant who has the fastest response time in Experiment 1

>> [val,idx] = min(T.Experiment1);
>> T.ParticipantID(idx)
ans = 507

Best Answer

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MATLAB: Display the ID of the participant who has the fastest response time in Experiment 1

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