how to find position of an element in a matrix which is present in another matrix?

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ASHA PON 2022-4-26

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https://ww2.mathworks.cn/matlabcentral/answers/1705380-how-to-find-position-of-an-element-in-a-matrix-which-is-present-in-another-matrix

评论： ASHA PON 2022-4-26

I am having two matrix. Selected elements in one matrix is present as elements in another matrix. Now i need to find the position of selected elements in the original matrix.

For example:

a=[0.74 0.71 0.604 0.47 0.59 0.58 0.75];

b=[0.604 0.75];

Expected output:

c=[3 7]

I need to apply this problem to a larger n*m matrix.

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Stephen23 2022-4-26

Do not use ISMEMBER (unless you really know what you are doing with binary floating point numbers).

Use ISMEMBERTOL instead.

ASHA PON 2022-4-26

Thank you for your reply.

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Answer 1

DGM 2022-4-26

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https://ww2.mathworks.cn/matlabcentral/answers/1705380-how-to-find-position-of-an-element-in-a-matrix-which-is-present-in-another-matrix#answer_951215

编辑：DGM 2022-4-26

在 MATLAB Online 中打开

a=[0.74 0.71 0.604 0.47 0.59 0.58 0.75];
b=[0.604 0.75];
% get the index of matches
% ainb are the indices of elements of a which are in b
% bina is a logical array describing which elements of b are in a
[bina ainb] = ismember(b,a)
bina = 1×2 logical array
   1   1
ainb = 1×2
     3     7
% get the matched values
a(ainb)
ans = 1×2
    0.6040    0.7500