Find the minimums along 3rd dimension of an array

Question

Bill Tubbs 2021-12-9

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https://ww2.mathworks.cn/matlabcentral/answers/1607425-find-the-minimums-along-3rd-dimension-of-an-array

编辑： Bill Tubbs 2021-12-10

I have a 3d array that is constructed from two 2d arrays:

a = [1 2 3; 4 5 6; 7 8 9];
b = [1 2 0; 4 0 9; 9 8 9];
c = cat(3,a,b);

I want to find the minimums along dimension 3 only.

Desired output:

c_mins =

1 2 0

4 0 6

7 8 9

I thought this would work but it seems to give a different result which I don't understant:

min(c, 3)

ans(:,:,1) =

1 2 3

3 3 3

ans(:,:,2) =

1 2 0

3 0 3

3 3 3

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Answer 1

Image Analyst 2021-12-9

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https://ww2.mathworks.cn/matlabcentral/answers/1607425-find-the-minimums-along-3rd-dimension-of-an-array#answer_851705

在 MATLAB Online 中打开

You need [] in min():

a = [1 2 3; 4 5 6; 7 8 9];
b = [1 2 0; 4 0 9; 9 8 9];
c = cat(3,a,b)
c = 
c(:,:,1) =

     1     2     3
     4     5     6
     7     8     9


c(:,:,2) =

     1     2     0
     4     0     9
     9     8     9
minValues = min(c, [], 3)
minValues = 3×3
     1     2     0
     4     0     6
     7     8     9

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Image Analyst 2021-12-10

@Bill Tubbs, yeah, sometimes there are inconsistencies like that.

Steven Lord 2021-12-10

If I recall correctly the syntax min(A, B) predates the introduction of 3-dimensional arrays into MATLAB (both of which predate the start of my tenure at MathWorks.) We don't want min(A, scalar) to be ambiguous if the scalar is a potential dimension number so we instead treat it always as B.

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