Get all row indices where values of to columns reach their maximum

Hey,

i would like to get an array containing the indices of all rows in which the values of column 2 and 3 reach their maximum at the same time.

Example:

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

Output should be an array containing the values 2 and 3 corresponding to row 2 and 3 of array A since the values in column 2 and 3 both reach their maximum at the same time.

Output = [2 3];

Thank You :-)

Answer 1

[Les Beckham]

A = [1 2 3;
     1 4 3;
     2 4 3;
     1 4 2];
m = max(A(:,2:end), [], 1)

m = 1×2

4 3

Output = find(all(ismember(A(:,2:end), m), 2))

Output = 2×1

2 3

[Georg Bauer]

Awesome! Thank you!

[Les Beckham]

You are quite welcome.

[Voss]

@Georg Bauer: What should Output be when A is as follows?

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

% get column-wise maxima:
m = max(A(:,2:end), [], 1);

The given answer will give [2; 3] since rows 2 and 3 both have all values in their 2nd and 3rd columns as elements of the column-wise maxima m ([3 4]):

Output = find(all(ismember(A(:,2:end), m), 2))

Output = 2×1

2 3

But I think you want the result to be row 2 only, since that's the only row where the column-wise maxima occur in the same row, in which case you can use this logic, to compare elements in each column individually:

Output = find(all(A(:,2:end) == repmat(m,size(A,1),1), 2))

Output = 2

[Les Beckham]

Good catch, Voss. Thanks for pointing that out.