Having trouble with looping through fields in a struct

So I want to loop through a folder containing several .txt files. So, i start by choosing the folder where I want to work in and collect my files, here all files are formed as 21x2 double. Then I am trying to retrive data from the fields into seperate variabels, since when I collected them it was saved as a 8x1 struct, hence 8 fields(8 files of the size 21x2 double). And I want to end up with 2 variables of the form 21x1 double.

% Evaluation of mean bias for group
files.path='';

disp('Choose directory to work in');
path = uigetdir('');

list = dir(fullfile(path,'*.txt'));
data.t = zeros(length(list));
data.p = zeros(length(list));
for i = 1:length(list)
   [data.t{i}, data.p{i}] = textread(list(i).name);
end

But, instead I get this error message

Unable to perform assignment because the left and right sides have a different number of elements.

Error in mean_bias (line 15)

[data.t(i), data.p(i)] =textread(list(i).name);

I am not sure of how to solve this, because when I earlier today wrote anoter pice of code in a similair way it worked without problem. only difference here is that in every file the first column is the same for every file I loop over and that is why I choose not to save those values in every iteration.

files.path='';

disp('Open BSIF input file');
[file path]=uigetfile([files.path '*.txt; *.crv; *.inp'],'Open input function file','MultiSelect','off');
files.inp=[path file];

list = dir(fullfile(path,'*.txt'));
for i = 1:length(list)-1
    [t_tac, IDIF{i}] = textread(list(i+1).name);
    a = IDIF{i}';
    hold on
    plot(t_tac*60,a)
end

Anyone that could have an idea of how to solve this?

[Matt J]

Error in mean_bias (line 15)

[data.t(i), data.p(i)] =textread(list(i).name);

Note that this error message does not match the code you posted for us above. There, the left hand side had brace indexing [data.t{i}, data.p{i}]

[Amanda Eriksson]

Oh thank you! I had tried so many types of way to save to new variables that I must have forgett to chaneg back to what I originally had!

It is now working, and I also removed the matrox definition, but I thought I already had tried that and it didn't work.. weird. But it works now! Thanks again :)

Answer 1

[Joseph Cheng]

primarily its because of the

data.t = zeros(length(list));
data.p = zeros(length(list));

where you've set the t and p to be a matrix. but then when you are in the for loop you're trying to stuff the items into a existing matrix array index but trying to access it as a cell with probably a string. in your previous code you didn't pre-define what t and p were in the struct so matlab was able to correctly assign what it was.

[Amanda Eriksson]

Oh okey, I thought that by doing zeros, that it only alocated memory, so that I wouldn't get the message that data.t and data.p changed its size at every iteration. But I will remeber this for next time using cells!

And it works now, I must have changed the code to many times that was maybe why it didn't ad up!

Thank you:)

[Joseph Cheng]

It's generally a good idea. There is a way to preallocate for cells too but I forget. Mat2cell comes mind but unless you're dealing huge arrays or doing it many many times the overall efficiency isn't worth just ignoring the warning.