Looping through sets of names for a match and selecting variable with this name

Hi there! I've got a simple question:

I've got the following code below (ar at least this is a more reproducible version of it; note my .set files are not something I can share on here):

name=dir('*data.set');
name={name.name};

accvectors=[1,1,0,0,1;1,0,0,1,1;1,0,0,1,1]
accvectors_name={'500','501','502','503','504'}
accvectors=cell2table(num2cell(accvectors),'VariableNames',accvectors_name)

for b=1:length(name);
	filename = name{b};

[EEG] = pop_loadset(filename);

% match the file to the correct vector of trials
ID = filename(1:3)  %just selecting the participant number between 500-599, from a longer file name

for xx = 1:length(accvectors_name);   
    if xx == ID
       part_vector = accvectors{xx}   
    end
end

end

It is the last 6 lines of code that are a problem. The rest works.

What I want to do is: when the variable name in 'accvectors' matches 'ID', I'd like to select the corresponding 'accvectors' column and save it into 'part_vector'. There is certainly something wrong because instead of a value between 500 and 599 (in my longer dataset), 'xx' just outputs the total count of values (84).

Could someone direct me to where my logic is wrong?

Answer 1

[Voss]

You're comparing a numeric index (xx), which is between 1 and length(accvectors_name), with a length-3 character vector (ID). Instead, compare character vectors to character vectors.

Also, use two subscripts with {}, or use .() with a column name or index to access a table's contents.

accvectors=[1,1,0,0,1;1,0,0,1,1;1,0,0,1,1];
accvectors_name={'500','501','502','503','504'};
accvectors=cell2table(num2cell(accvectors),'VariableNames',accvectors_name)

accvectors = 3×5 table
    500    501    502    503    504
    ___    ___    ___    ___    ___

     1      1      0      0      1 
     1      0      0      1      1 
     1      0      0      1      1 

ID = '503';

for xx = 1:length(accvectors_name)
    if strcmp(accvectors_name{xx}, ID)
        
%         part_vector = accvectors{xx} % this is incorrect

%         part_vector = accvectors{:,xx} % these four all do the same thing
%         part_vector = accvectors.(xx)
%         part_vector = accvectors.(accvectors_name{xx})
        part_vector = accvectors.(ID)
        
    end
end

part_vector = 3×1

0 1 1

Answer 2

[Stephen23]

replace

if xx == ID

with

if strcmp(ID,accvectors_name{xx})

"There is certainly something wrong because instead of a value between 500 and 599 (in my longer dataset), 'xx' just outputs the total count of values (84). "

This is how you defined xx:

for xx = 1:length(accvectors_name);

And so that is exactly what xx is: the integers from 1 to ... 84, apparently. After defining xx to have exactly those values, how do you expect xx to have some other completely different values?

A simpler approach using STRNCMP and logical indexing and no table:

V = [1,1,0,0,1;1,0,0,1,1;1,0,0,1,1];
C = {'500','501','502','503','504'};
S = dir('*data.set');
for k = 1:numel(S)
    F = S(k).name;
    X = strncmp(F,C,3);
    M = V(:,X)
end