reshaping a matrix: adding rows and changing the selected elements of the original matrix

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Jan Morawietz 2014-11-27

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https://ww2.mathworks.cn/matlabcentral/answers/164525-reshaping-a-matrix-adding-rows-and-changing-the-selected-elements-of-the-original-matrix

评论： Geoff Hayes 2014-11-27

采纳的回答： Geoff Hayes

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Take the following matrix A:

A = [ 1 2 3 4 5 6]';

If I want to find the max. and min. for a predefined frequency (e.g. frequency of 3 elements) I reshape matrix A by defininga columns for every frequency I want to evaluate. After, I can look for the min. and max. of each column.

E.g.

Frequency = 3

A1 = reshape [A,3,2];
MX1 = max(A1,[],1); 
MN1 = min(A1,[],1);

So frar so good. However, does anyone have an idea of how to change this code when the frequency should increase by one step for every column? In other words, matrix A1 should actually equal the following format:

Thank you for any advice!

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Jan Morawietz 2014-11-27

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So my plan now is to change A in advance. somth like

A11 = zeros(3,4);
for n = 1 : 2
      A11(:,n) = A1(:,n)+n;
end

SO how do I make to the loop stop at 6?

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Answer 1

Geoff Hayes 2014-11-27

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Jan - you could try using arrayfun to apply a function to each value in the first row, building a column for each. Perhaps something like

A1 = cell2mat(arrayfun(@(x)(x:x+2)',1:4,'UniformOutput',false));

In the above, we provide the first row of your output matrix as 1:4 or [1 2 3 4], then for each of these elements, we build a column as (x:x+2)'. As the output from arrayfun is a cell array, we need to convert it to a matrix with cell2mat. Try it and see what happens!