Extract elemnts from a matrix and put them in a new one

Question

Gio Torres 2021-4-2

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/790689-extract-elemnts-from-a-matrix-and-put-them-in-a-new-one

回答： Matt J 2021-4-2

Hello everyone,

I'm looking for a command or an algorithm able to solve the following problem:

I have a matrix M in which there are many zeros with decimal values and few elements which are higher than 0.99 such as this matrix:

M=[ 0.45 5.45 0.64 0.78 0.32

3.65 0.79 0.56 0.23 0.11

0.21 6.78 0.55 3.45 0.57

0.67 9.54 5.44 9.00 3.23]

I would like to make a new matrix N by extracting the elements of matrix M which are larger than 1 with a certain arrangement like this:

N=[ 3.65 5.45 5.44 3.45 3.23

NaN 6.78 NaN 9.00 NaN

NaN 9.54 NaN NaN NaN]

Thanks for your attention :)

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Matt J 2021-4-2

Are you going to explain to us what the pattern of NaNs is supposed to be in the output N?

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Answer 1

Image Analyst 2021-4-2

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链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/790689-extract-elemnts-from-a-matrix-and-put-them-in-a-new-one#answer_665124

在 MATLAB Online 中打开

Try this:

M=[ 0.45  5.45  0.64  0.78  0.32
	3.65  0.79  0.56  0.23  0.11
	0.21  6.78  0.55  3.45  0.57
	0.67  9.54  5.44  9.00  3.23]
[rows, columns] = size(M)
MOut = nan(size(M));
for col = 1 : columns
	thisCol = M(:, col)
	moreThan1 = thisCol(thisCol >= 1)
	for row = 1 : length(moreThan1)
		MOut(row, col) = moreThan1(row);
	end
end
% Get rid of any all non rows
rowsToDelete = all(isnan(MOut), 2);
MOut(rowsToDelete, :) = []

You get

MOut =

3.65 5.45 5.44 3.45 3.23

NaN 6.78 NaN 9 NaN

NaN 9.54 NaN NaN NaN

If it's not your homework assignment, you can use this code.

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Answer 2

Matt J 2021-4-2

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链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/790689-extract-elemnts-from-a-matrix-and-put-them-in-a-new-one#answer_665214

在 MATLAB Online 中打开

sortlidx.m

Using the attached file sortlidx.m

M=[    0.45  5.45  0.64  0.78  0.32
       3.65  0.79  0.56  0.23  0.11
       0.21  6.78  0.55  3.45  0.57
       0.67  9.54  5.44  9.00  3.23];
N=M; 
N(N<1)=nan;
[~,is]=sortlidx(isnan(N));
N=N(is);
N(all(isnan(N),2),:)=[]
N = 3×5
    3.6500    5.4500    5.4400    3.4500    3.2300
       NaN    6.7800       NaN    9.0000       NaN
       NaN    9.5400       NaN       NaN       NaN