Matlab create cell array using a loop

Question

As part of a university project, I have to do the following: Use a database that contains 14 different folders (14 different subjects) and in every folder we have 5 trials of 12 different activities stored in .mat files. The trials files contain 6 columns (of which I want only 3) and different size of rows. Now I want to concatenate the 5 trials in one .mat folder for every subject, and store all the database to the following format : subject x activity x trial .

I have written the following code:

InPath_data = 'C:\Users\olga\Desktop\USC-HAD\';

listname = [InPath_data, 'Subjects.txt'];
folder_subject = textread(listname,'%s','delimiter','\n','whitespace','');
listname = [InPath_data,'ActivityTrial.txt'];
files_act_tr = textread(listname,'%s','delimiter','\n','whitespace','');
fname = [InPath_data,folder_subject{1},'\',files_act_tr{1},'.mat'];
tmp1= [];
k=1;
for i=1:length(folder_subject)
    for j=1:length(files_act_tr)
        fname = [InPath_data,folder_subject{i},'\',files_act_tr{j},'.mat'];
        tmp= load(fname);
        q=tmp.sensor_readings( : ,(1:3));
        tmp1= cat(1,tmp1,q);
        clear q;
        if mod(j,5)==0
         data(j-4*k,:,:)=tmp1;
         k=k+1;
         tmp1=[];
        end
    end
end

Now when clearing tmp1 i cannot use the loop. I suspect that using cell arrays is the key to do what I want, but I have never used them before, so... Any help would be appreciated! :)

??? Undefined function or variable 'tmp1'. Error in ==> script at 18 tmp1= cat(1,tmp1,q); — Pola
– Pola, Commented Oct 19, 2013 at 13:59

Daniel · Accepted Answer · 2013-10-19 13:59:48Z

1

clear tmp1; deletes the variable, in the next iteration the variable tmp1 is unknown like it was never used before. Using tmp1=[] instead empties the variable. This should fix your code.

answered Oct 19, 2013 at 13:59

Daniel

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4 Comments

Pola Over a year ago

This did the job, but now I get another error : Subscripted assignment dimension mismatch. Error in ==> script at 21 data(j-4*k,:,:)=tmp1; The thing is I need a code that loops through the .mat files and stores every five of them in one .mat file, for each user 'i' who performs an activity 'j'. The subject folders contain files in this format: a1t1 ,a1t2,a1t3,a1t4,a1t5 , a2t1,a2t2,a2t3,a2t4,a2t5.....a12t1,a12t2,a12t3,a12t4,a12t5. Where a(i) represents the 14 activities and t(i) the trials

Daniel Over a year ago

Please update your question, the line data(j-4*k,:,:)=tmp1; does not exist in the code. Is it correct that j starts at 2? Think it should be for j=1:length(files_act_tr)

Pola Over a year ago

Hey Daniel. Thank you for your reply and sorry for the badly formed question. To my defence it's my very first post here, hope to get better after time. I managed to solve the problem myself. The last error I got was due to the fact that the size of tmp1 was not stable, so I had to extract a 10000x3 slice of every trials table to make it work, as I posted above. Anyway, thanks for everything! :)

slbass Over a year ago

Since this answer fixed your problem, you should mark it as the accepted answer to give @DanielR the rep

Pola · Accepted Answer · 2013-10-20 10:34:14Z

Edit: I managed to do it, by setting a stable array size for trials to 10000x3.Otherwise, the size changes over loops and the 4 D matrix cannot be formed properly. Using @Daniel R solution tmp1=[] and some other alterations, the code goes like this:

InPath_data = 'C:\Users\olga\Desktop\USC-HAD\';

listname = [InPath_data, 'Subjects.txt'];
folder_subject = textread(listname,'%s','delimiter','\n','whitespace','');
listname = [InPath_data,'ActivityTrial.txt'];
files_act_tr = textread(listname,'%s','delimiter','\n','whitespace','');
fname = [InPath_data,folder_subject{1},'\',files_act_tr{1},'.mat'];
tmp1= [];
k=1;

for i=1:length(folder_subject)
    for j=1:length(files_act_tr)
        fname = [InPath_data,folder_subject{i},'\',files_act_tr{j},'.mat'];
        tmp= load(fname);
        q=tmp.sensor_readings( : ,(1:3));
        tmp1= cat(1,tmp1,q);
        clear q;

        if mod(j,5)==0

         data(i,j-4*k,:,:)= tmp1((1:10000), :);
         k=k+1;
         tmp1=[];

        end

    end
   k=1;
end

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