# How can I assign a variable to all the columns and all the rows of a matrix?

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Mau Dudas 2019 年 10 月 23 日

Got a 20x10 double matrix and I'd like to assign 'numsub' to the number of rows and 'numtrials' to the number of columns in the whole matrix so that I can use them as an index in a for loop for extracting values from certain subjects.
I will need to do something like this:
for i = 1:numsubs
disp(['sub' num2str(i)])
disp('Slow trial')
for j=1:numtrials
if RT(j,i)<=0.3
disp(['trial' num2str(j)])
end(x3)

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### 採用された回答

Jos (10584) 2019 年 10 月 23 日
Are you looking for the function SIZE?
data = rand(20,10) ;
[numsubs, numtrials] = size(data)

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### その他の回答 (1 件)

Bob Thompson 2019 年 10 月 23 日
You don't need to actually create a new variable for this, you can just use the results from size.
A = randi(100,20,10);
[r,c] = size(A); % Where r is the number of rows, and c is the number of columns
% You can also just put the function directly into your loop
for i = 1:size(A,1)
...
for j = 1:size(A,2)
...
end
end

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