How to create indices for the k-fold cross-validation?

Hi All,

I'd like to create indices for the k-fold cross-validation using

indices = crossvalind('Kfold',Labels,k);

The "Labels" is a 1-by-1000 cell array which contains 1000 cells, as follows

  Labels(1: 10) = 1×10 cell array

  Columns 1 through 9

    {1×1 cell}    {1×1 cell}    {1×1 cell}    {1×1 cell}    {1×1 cell}    {1×1 cell}    {1×1 cell}    {1×1 cell}    {1×1 cell}

  Column 10

    {1×1 cell}
    
    
    
    Labels{1}= 1×1 cell array

    {'2'}

I got this error

Undefined function 'crossvalind' for input arguments of type 'cell'.

So, I took the following steps to solve the issue

Label_1 = cellfun(@(x) str2double(x), Labels, 'UniformOutput',false);
Label_double = [Label_1{:}]
indices = crossvalind('Kfold',Label_double,10);

And now I am dealing with the following error

Undefined function 'crossvalind' for input arguments of type 'char'.

I'm not sure why I get this error. any idea? Thanks!

[Susan]

Any idea?

[Megumi Fukuda]

Could you upload your label variable (you can upload .mat file) so that I can have a look? I assume your label is what-I-call 'nested' and that's why you cannot use crossvalind.

[Susan]

@Megumi Fukuda Sure thing! The label is attached.Thank you so much in advance for your help.

Answer 1

[Megumi Fukuda]

indices = crossvalind('Kfold',Labels,k);

I am sure this does not work, as the cells in the variable Label are nested and cannot be used for crossvalind without converting the variables.

I have tested this code with MATLAB 2021a and this code looks fine. Would you like to try your code again?

% clear the workspace
load('Label.mat'); % the mat file you uploaded
Label_1 = cellfun(@(x) str2double(x), Giant_bpm, 'UniformOutput',false);
Label_double = [Label_1{:}];
indices = crossvalind('Kfold',Label_double,10);

(... and here is another implementation I came up with. This returns the label as char type)

load('Label.mat');
Giant_bpm_updated = cellfun(@cell2mat, Giant_bpm(:), 'UniformOutput', false);
indices = crossvalind('Kfold',Giant_bpm_updated,10);

Hope this helps!

[Susan]

Thanks for your response.

Interesting! when I run my code I get the same error as before but your code works fine.