Find series of maxima of array (and matrix) within blocks of size n

Question

Erez 2019-8-30

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/478259-find-series-of-maxima-of-array-and-matrix-within-blocks-of-size-n

评论： Erez 2019-8-30

采纳的回答： Ted Shultz

I have a simple problem, and it's, perhaps, less simple extension:

I have an array A=[1 2 5 1 0 0 5 0 1 2 4 0 5 3 2 0 1 0 0 5] (all positive). How do I produce a vector B, which contains the maxima of, say, blocks of n=5 within A?

Namely, I want to produce B=[5 5 5 5].

2. I have a matrix: A=[1 2 5 1 0 0 5 0 1 2 4 0 5 3 2 0 1 0 0 5; 1 2 5 1 0 0 7 0 1 2 4 0 7 3 2 0 1 0 0 5; 1 2 5 1 0 0 5 0 1 2 4 0 5 3 2 0 1 0 0 5;] . Now, I want to get the matrix: C=[5 5 5 5; 5 7 7 5; 5 5 5 5] .

Can these two tasks be achomplished with a single procedure, without using loops?

Thanks!

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Answer 1

Ted Shultz 2019-8-30

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https://ww2.mathworks.cn/matlabcentral/answers/478259-find-series-of-maxima-of-array-and-matrix-within-blocks-of-size-n#answer_389772

编辑：Ted Shultz 2019-8-30

在 MATLAB Online 中打开

You could use rehsape and max:

[reshape(max(reshape(A',5,[])), [], size(A,1))]'

Test:

A=[1 2 5 1 0 0 5 0 1 2 4 0 5 3 2 0 1 0 0 5] 
[reshape(max(reshape(A',5,[])), [], size(A,1))]'
A=[1 2 5 1 0 0 5 0 1 2 4 0 5 3 2 0 1 0 0 5; 1 2 5 1 0 0 7 0 1 2 4 0 7 3 2 0 1 0 0 5; 1 2 5 1 0 0 5 0 1 2 4 0 5 3 2 0 1 0 0 5;] 
[reshape(max(reshape(A',5,[])), [], size(A,1))]'

ans =

5 5 5 5

ans =

5 5 5 5

5 7 7 5

5 5 5 5

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Erez 2019-8-30

Thanks a lot!

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Answer 2

Bruno Luong 2019-8-30

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/478259-find-series-of-maxima-of-array-and-matrix-within-blocks-of-size-n#answer_389776

编辑：Bruno Luong 2019-8-30

在 MATLAB Online 中打开

maxfun =  @(A) squeeze(max(reshape(A,size(A,1),5,[]),[],2));
A = [1 2 5 1 0 0 5 0 1 2 4 0 5 3 2 0 1 0 0 5]
B = maxfun(A)
A = [1 2 5 1 0 0 5 0 1 2 4 0 5 3 2 0 1 0 0 5; 1 2 5 1 0 0 7 0 1 2 4 0 7 3 2 0 1 0 0 5; 1 2 5 1 0 0 5 0 1 2 4 0 5 3 2 0 1 0 0 5]
C = maxfun(A)

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Erez 2019-8-30

Awsome solution! I can't formally accept two solutions on this website, so I'll "accept" the first (arbitrarily). But this solution of yours works just as great. Thanks!

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