How to extract data stored in a matrix and in a specific range of columns whose number is stored in another matrix?

Hi, I am new to Matlab and I would be grateful if you could give me a hand.

I have several waveform data from various participants in a matrix (in raws). This is how the data look like in Matrix1 (which does not have the text at the beginning of the raw, I added it to simplify the explanation):

'ParticipantID'	        202	202	202 [...] 203 203 203 [...]
    'Stage'	             0	  0	  0 [...]   0	0	0 [...]
    'Frame'	             1	  2	  3 [...]   1	2	3 [...]
    'flexion'	         69  68	 69 [...]  72  73  74 [...]
    'ext/int rotation'	-14	-13	-11 [...] -15 -15 -16 [...]
    'abd/adduction'	      5	  4	  0 [...]   2   3   2 [...]
    'ml shift'	         -7	 -7	 -7 [...]  -4  -4  -5 [...]
    'ant/post draw'	     14	 15	 16 [...]  16  18  19 [...]
    'distal comp'	     25	 25	 25 [...]  20  20  20 [...]

As you can see, the waveform data for different participants come in succession.

I have another matrix (Matrix2) with one raw only. The numbers refer to the column number in Matrix1 where the data for a different participant start. Matrix2 looks like this:

    1	221	463	675	903	1096	1367	1574 [...]   3888

This means that data for participantID 202 range from column 1 up to column 220 of Matrix1, participantID 203 data start from column 221 up to column 462, etc.

I would like the code to pick the data for each participant, separately. I wrote a for loop:

    for i = 1:size(Matrix2)
    B1 = Matrix2(1, i);
    for k = 2:size(Matrix2)
        B2 = Matrix2(1, k);
    end
    EachPatientData= Matrix1(:, B1:B2-1);
    end

I do not get any error message when I run the code but obviously I cannot see what the loop is doing and I think I am only getting the last data displayed in the workspace, so B1=3888, B2=3888 and EachPatientData is empty (no surprise here).

Is the procedure I am following right?

How can I see the data extracted with each of the loop iterations to make sure I am going in the right direction?

Many thanks!

Answer 1

[dpb]

It would be much simpler if you would use a table for each variable and include the ParticipantID as a variable instead.

However, unless the time series are the same length for each, you can't use a table to hold all the data together unless you use a missing value indicator for the shorter series as arrays in MATLAB must be rectangular. The alternative is a cell array which can hold arrays of different lengths in different cells.

However, given the stucture you have, the simpler way to pull the information is to use logical indexing/addressing on the ID in the data array itself; this way you can eliminate the second indexing array.

uID=unique(M(1,:));                         % get the unique IDs (M is shorthand for your Matrix1)
for i=1:numel(uID)                          % iterate over the list of IDs
   P{i}=M(ismember(M(1,:),uID(i)),4:end);   % extract 4th and subsequent rows for each column
end

[MD]

Hi and thank you for your help.

The time series are the same length for each participant but are different lengths between participants. I tried to organise the data in a table but being a beginner, I found myself struggling to understand how to work with the data in this fashion. I tried the code you suggested but unfortunately, I get an unspecified error for this line P{i}=M(ismember(M(1,:),uID(i)),4:end);

[dpb]

Attach the M1 array as a .mat file so we can test something out instead of just air code...or at least show us the code in its entirety including the error message; we can't debug what we can't see.