Get max value and index of multidimensional array

hello

i have an output value matrix depending on 3 inputs ranging from p10 to p11 , p20 to p21, p30 to p31. the output matrix is multidimensional depending on number of inputs. i want to write a function that gives the max value and its coordinates so to speak of the max value. matlabs max function only does 1 dimension.

any help would be grateful. thank you

Answer 1

[ChristianW]

Use 1D-Indexing:

M = randn(10,10,10,10);
[C,I] = max(M(:));
C
M(I)

This might be useful too:

[I1,I2,I3,I4] = ind2sub(size(M),I);
M(I1,I2,I3,I4)

[Evan]

The second part is exactly what I needed. Absolutely brilliant.

Thanks!

[Nathan White]

I tried using this myself, but I'm not understanding how to do it. I have a 10 x 10 x 10 matrix and I need to find which row, column and page gives the max value. Could you clarify a little more what you did here? Thanks.

Answer 2

[David McMahon]

Using more modern versions of Matlab, I found a simple solution that works for any size of matrix:

In the case of, say, 3D:

[M,I] = max(A,[],"all","linear");
[dim1, dim2, dim3] = ind2sub(size(A),I)

[Steven Lord]

To generalize the last line:

% Sample data
nd = randi([2 10]); % random integer between 2 and 10
sz = randi(4, 1, nd) % vector of nd integers representing size(A)

sz = 1×7

4 1 2 3 2 3 3

A = randi([-10 10], sz); % random array

% Your first line
[maxValue, maxInd] = max(A, [], "all", "linear")

maxValue = 10

maxInd = 58

% Allocate a cell array to contain the subscript indices
d = cell(1, ndims(A));
% Use the cell array as a comma-separated list to hold the indices
[d{:}] = ind2sub(size(A), maxInd)

d = 1×7 cell array
    {[2]}    {[1]}    {[1]}    {[2]}    {[1]}    {[2]}    {[1]}

% Convert the subscript indices back into a linear index
checkInd = sub2ind(size(A), d{:})

s = 58

% Use the subscript indices to get the element from A
checkValue = A(d{:})

checkValue = 10

Answer 3

[Youssef Khmou]

Hi, try this function

 function [Max,index] =Max3d(x)

 N=size(x);
 if length(N)<3
    error(' Input 3D array');
 end

 [a,t]=max(x(:));
 Max=a;
 index1=ceil(t/(N(1)*N(2)));

 %Now we find the slice that contains the Max
 Temp=x(:,:,index1);

 [index2,index3]=find(Temp==max(Temp(:)));

 index=[index2;index3;index1]';

[Youssef Khmou]

i tried to use ceil for referencing the slice, but i am not sure if that is true for each case.

[ChristianW]

I dont get your reason for this.

[Youssef Khmou]

@ChrisitanW : what do you mean ?

[ChristianW]

1. max(x(:)) is the same answer given twice and
2. Why not just use ind2sub for index?

[Youssef Khmou]

ChrsitanW : please try the function and see if is it the same approach/ answer you gave or not .

Of course it also uses max(G(:)) but from there, you can find z coor, then x and y using built-in functions "ceil" and "find" .

[ChristianW]

Eheh, yeah its the same, but ind2sub is a validated function working for all dimensions. But its fine, your approach can be useful for someone.

Answer 4

[Anxo Tato]

For a 2-D matrix this code can help. It calculates the indices (row and column) of the maximum (value) of a matrix A. Attention: It doesn't deal with multiple maximums!

function [row,column,value] = max_matrix(A)

[y,in] = max(A);

[value,column] = max(y);

[~,row] = max(A(:,column));

end

[Mohammad Torabi]

Good, I found an easier way to get column:

[value,column] = max(max(A));

[~,row] = max(A(:,column));