Matlab: Find minimum value from a set of values for each column in an array

Question

I have a 2-D array A=zeros(1000,1024) . I want to iteratively compute the difference between each of the value of the i-th row (with i=1-999) and the values of 1000th row.

Right now I think of looping over the 1-999 rows, compute the differences of the current row and the 100th row and store it in a seperaate data structure ( B=zeros(999,1024) ). After, I compute the minimum of each column using another for-loop, which iterates over the columns of B .

Do you know of a more efficient, faster approach?

Answer 1

如果只希望每列的最小值，那么可以通过在最后进行减法来节省许多操作：

min(A(1:end-1,:),[],1) - A(end,:)

Answer 2

Try this -

min(bsxfun(@minus,A(1:999,:),A(1000,:)),[],1)

It seems you want to subtract from the last row, so you can make it general -

min(bsxfun(@minus,A(1:end-1,:),A(end,:)),[],1)

Answer 3

This is a classic use case for bsxfun :

M = rand(1000,1024);
V = M(end,:);

MminusV = bsxfun(@minus, M(1:end-1,:), V);

min(MminusV)