Extracting every row from a matrix using a for loop

I'm working with some velocity data and have a matrix 23,999x31.

I'm new to using Matlab, I'm able of extracting one row but would now like to be able to create a for loop that will allow me to extract each of the 23,999 rows in the matrix.

Any help for a Matlab novice would be greatly appreciated!

Answer 1

[Rik]

This might not be optimal, depending on what you want to do, but the size function is here to help:

data=rand(23999,31)
for row=1:size(data,1)
    rowdata=data(row,:);
    
    %do something with that row here
    
end

[Edward Keavney]

Hi, thanks for your response.

Are you aware of a format whereby I can write a loop that takes the data from every row of the 23,999 matrix? So starting with row 1 and extracting all the data in that row and then repeating the process for every row in the matrix, for all 23,999 rows?

[Rik]

Yes, that is what this code does. You can see for yourself. I would recommend trying this with a small example:

data=(1:5).'+rand(5,2);% row x will have values x.####
for row=1:size(data,1)
    rowdata=data(row,:);
    fprintf('row %d contains:\n',row)
    disp(rowdata)
end

row 1 contains:

    1.7313    1.7239

row 2 contains:

    2.4683    2.1095

row 3 contains:

    3.4510    3.8145

row 4 contains:

    4.9342    4.5450

row 5 contains:

    5.1155    5.7236

See?

If you want to use the entire matrix at once, there is no need to index it at all. If what I showed isn't what you want, please given an example of what it is you want.

[Edward Keavney]

Understood, thanks. I've been approaching the problem in the wrong way. I want to be able to determine the mean from each of the 23,999 rows. Can you help with this?

[Rik]

You can do that with the code I already posted:

data=(1:5).'+rand(5,2);% row x will have values x.####
for row=1:size(data,1)
    rowdata=data(row,:);
    mean(rowdata) %you can store this in a vector
end

ans = 1.1014

ans = 2.4187

ans = 3.5720

ans = 4.6323

ans = 5.6558

But it is better to use mean on the entire array:

mean(data,2) % specify the dimension to make it operate on the rows

ans = 5×1

1.1014 2.4187 3.5720 4.6323 5.6558