Reshaping a matrix with different column sizes to a vector

Hello,

Suppose you have a matrix that the number of columns for each row is different (the matrix is 100*132 but not every row has 132 data. Row 1 only has 21 columns and the rest is zero. Row 2 has 23 columns and the rest is zero and so on.

I want to reshape this matrix into a vector in which all of the rows of the original matrix are attached but I don't want the zeros. This is because I want to calculate the median of all elements and if I have the zeros, this will change the result.

For example, assume that the original matrix is:

M = [ 2 3 4 0 0 0; 1 3 6 2 1 0; 1 2 2 1 0 0 ]

and I want to reshape the above matrix to a vector like this:

A = [ 2 3 4 1 3 6 2 1 1 2 2 1 ]

that includes all numbers and excludes zeros.

I know the number of nonzero values in each row. They are available in an array like: Num = [3; 5; 4]

I tried this command but it did not work: reshape( M(:,1:Num(:,1)) , 1 , [])

It only considers the first value in Num and returns this vector instead:

[ 2 3 4 1 3 6 1 2 2 ]

Thank you for your help.

Answer 1

[Stephen23]

This code will concatenate exactly the number of values from each row, as given in Num, regardless of the values in the row:

M = [2 3 4 0 0 0; 1 3 6 2 1 0; 1 2 2 1 0 0];
Num = [3; 5; 4];

N = num2cell(M,2);
N = cellfun(@(v,n)v(1:n), N, num2cell(Num(:)), 'UniformOutput',false);
N = [N{:}];

For example if we change values at position Num in each row to zero:

M = [2 3 0 0 0 0; 1 3 6 2 0 0; 1 2 2 0 0 0 ];

then we correctly get

N = [2 3 0 1 3 6 2 0 1 2 2 0]

[Maryam Mohammadipour]

Thank you very much. Yes this worked.

Answer 2

[Mischa Kim]

Maryam, how about

 A = M';
 A(A==0) = []

[Maryam Mohammadipour]

Thanks for this. I think I still need to use reshape. M is a 3*6 matrix. Am I right?

[Mischa Kim]

Nope. This works as is. Just give it a try.

[Maryam Mohammadipour]

One other question, what if there are some zeros between the numbers that I want to have them. So only the number that I have in the Num vector tells me how many I want to include?