Subtracting 1 matrix from several columns in a larger matrix

Hi all, this is probably an easy one but my minds gone blank. Basically I have a matrix 3553450x8 containing different measured data, I am looking to subtract 3 of these columns by a seperate matrix. anyone know how to do this, cheers

[madhan ravi]

size of the other matrix?

[Jamie England]

the other matrix would be 3553450x1

Answer 1

[madhan ravi]

 M(:,1:3) - N
  %  ^^^---- represent three columns can be any three columns 
%M is of size 3553450x8 
%N is of size 3553450x1 

[madhan ravi]

See

https://www.mathworks.com/help/matlab/math/array-indexing.html

https://www.mathworks.com/help/matlab/matlab_prog/compatible-array-sizes-for-basic-operations.html

https://www.mathworks.com/company/newsletters/articles/matrix-indexing-in-matlab.html

Answer 2

[aara]

You could form a similar sized matrix of zeros, place the desired values which you wish to subtract from the original data and the perfrom the subtraction operation:

placeholder = zeros(3553450,8);
placeholder(:,i:j) = data_to_remove %choose i and j to be the columns you wish to subtract,
%  they must be adjacent to each other.
%if data is not adjacent to each other then do them manually via:
placeholder(:,i) = column1_data_to_remove;
placeholder(:,j) = column2_data_to_remove;
placeholder(:,k) = column3_data_to_remove;
dataMatrix = dataMatrix - data_to_remove;

Save on memory by using a sparse matrix with the placeholder.