load multiple .mat files

hi everyone,

I have a question.

I am analysing some data which have multiple subjects. Information about every subject is stored in the MATLAB structure (.mat file)

For Example:

U1_Acc_TimeD_FreqD_FDay.mat
U2_Acc_TimeD_FreqD_FDay.mat
U1_Acc_TimeD_FreqD_FDay.mat

and so on...

I would like to create for loop which in every iteration load new data_number.mat file.

I'd like in every iteration to load next .mat file? Particularly, I don't know how to address number part of filename using load function.

I tried this code and seems it's overwritten the data!

clear;
  for nc = 1:36
      load(['U', num2str(nc,'%2d'), '_Acc_TimeD_FreqD_FDay.mat']);
  end

Thank you

Answer 1

[Walter Roberson]

      load(['U_', num2str(nc,'%02d'), 'Acc_TimeD_FreqD_FDay.mat']);

or

      load( sprintf('U_%02dAcc_TimeD_FreqD_FDay.mat', nc) );

[neamah al-naffakh]

dear Walter Roberson, thank you very much. Just a small correction, if you don't mind because your code gives a simple error due to the file name

for nc = 1:36
load(['U', num2str(nc,'%2d'), '_Acc_TimeD_FreqD_FDay.mat']);
end

Again really your answer was so useful. thank you mate.

[neamah al-naffakh]

dear Walter Roberson, this code is uploading only the one mat file!! could you help me please? seems is data is overwritten!

[Walter Roberson]

Your question did not ask for the data to be stored separately.

   for nc = 1 : 36
      data{nc} = load( sprintf('U_%02dAcc_TimeD_FreqD_FDay.mat', nc) );
   end

This will give you a cell array of structures, with each structure containing one field for each variable that is stored in the .mat file.

If you already know the name of the variable you want to extract, then,

   for nc = 1 : 36
      file_data = load( sprintf('U_%02dAcc_TimeD_FreqD_FDay.mat', nc) );
      data{nc} = file_data.NameOfVariableGoesHere;
   end

This code does not assume that the size or data type of the stored information is all the same. If you know that it is vectors that are consistent length, then you could use

   for nc = 1 : 36
      file_data = load( sprintf('U_%02dAcc_TimeD_FreqD_FDay.mat', nc) );
      data(:,nc) = file_data.NameOfVariableGoesHere;
   end

after which the data would appear as columns, one column for each file.

[neamah al-naffakh]

Dear Walter Roberson,

I really appreciate your kind help.

I am trying to access each Struct inside the cell (data) and extract specific rows and columns.

I have written this code but it stores the data of the last Struct only!

 clear;
  for nc = 1 : 36
  data{nc} = load( sprintf('U%02d_Acc_TimeD_FreqD_FDay.mat', nc) );
  end

for j=size(data,2)
Feat_Vec1=(data{j}.Acc_TD_Feat_Vec(2:36,1:126)); 
end

could you help me with this please?

[Walter Roberson]

for j = 1 : size(data,2)
  Feat_Vec1(:,:,j) = data{j}.Acc_TD_Feat_Vec(2:36,1:126); 
end

This would create a 35 x 126 x 36 array

[neamah al-naffakh]

thank you so much, but actually, it doesn't give me the correct output!

*it converts the values of each struct into 0 :(*

please see

[neamah al-naffakh]

when I use this code, I get what I want but only for the last struct (36) in the cell data

 clear;
  for nc = 1 : 36
      data{nc} = load( sprintf('U%02d_Acc_TimeD_FreqD_FDay.mat', nc) );
  end

   for j=size(data,2)
    Feat_Vec1{j} = data{j}.Acc_TD_Feat_Vec(2:36,1:126); 
   end

please have a look on here !!

[neamah al-naffakh]

I have solved it but it's really weird !!

 clear;
  for nc = 1 : 36
      data{nc} = load( sprintf('U%02d_Acc_TimeD_FreqD_FDay.mat', nc) );
  end

   for j=1:36      *% instead of for j=size(data,2)*
    Feat_Vec1{j} = data{j}.Acc_TD_Feat_Vec(2:36,1:126); 
   end

[Walter Roberson]

Notice I had suggested

for j = 1 : size(data,2)

rather than

for j = size(data,2)

the second of those does only size(data,2)

[neamah al-naffakh]

dear Walter Roberson, many thanks for your help. I really appreciate it.