How can I obtain a certain value from the function 'find' from a 3x2 cell?

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Pietro Fedrizzi 2021-10-21

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评论： Pietro Fedrizzi 2021-10-22

I need a certain variable "a" to be equal to either 1,2 or 3 according to two previous selection "Firstselection" and "Secondselection" which algo go from 1 to 3.

I have a 3x2 cell Comb = [1,2; 2,3; 1,3]. I have to assign "a" to a find function so that when Firstselection = 1 & Secondselection = 2 (and viceversa), a = 1, Firstselection = 2 & Secondselection = 3 (and viceversa), a = 2 and Firstselection = 1 & Secondselection = 3 (and viceversa), a = 3, all based on the cell Comb. I already solved it with an if cycle but now I need to apply the function find to the cell to obtain a certain value of "a" according to my 2 selections. I cannot change the cell.

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Pietro Fedrizzi 2021-10-21

Firstselection = 1 | 2 | 3; %identified by a numeric slider

Secondselection = 1 | 2 | 3;

Comb = {1,2;2,3;1,3};

Comb = 3×2 cell

% 'a' has to be either 1,2,3 according to my selection as I said previously.

% (Firstselection =1 & Secondselection =2 (and viceversa) -> a = 1, and so on...

% Is there a way to obtain that using the find

% function?

dpb 2021-10-22

Just repeating the same unclear verbiage doesn't help -- SHOW us the input and corresponding output expected.

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Answer 1

Dave B 2021-10-21

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在 MATLAB Online 中打开

I think you're asking how to search for the index of a row in a matrix based on multiple columns (although you have a cell array, you can just convert that to start).

You'll want to think about a few 'special' cases: what if it isn't found? What if it's found in more than one place? ismember does a nice job if you're not concerned with the multiple result issue:

comb={1,2;3,4;1,3};
comb_mat=cell2mat(comb);
target=[1 2];
[~,wherefound]=ismember(target,comb_mat,'rows')
wherefound = 1
target=[3 4];
[~,wherefound]=ismember(target,comb_mat,'rows')
wherefound = 2
target=[1 3];
[~,wherefound]=ismember(target,comb_mat,'rows')
wherefound = 3
target=[12 13];
[~,wherefound]=ismember(target,comb_mat,'rows') % wherefound will be 0 if not found
wherefound = 0
comb={1,2;3,4;1,3;1,2};
comb_mat=cell2mat(comb);
target=[1 2];
[~,wherefound]=ismember(target,comb_mat,'rows') % wherefound will be the first index if multiple occurrences
wherefound = 1

Otherwise you can combine find with an &:

comb={1,2;3,4;1,3};

comb_mat=cell2mat(comb);

target=[1 2];

find(comb_mat(:,1)==target(1) & comb_mat(:,2)==target(2))

ans = 1

target=[3 4];

find(comb_mat(:,1)==target(1) & comb_mat(:,2)==target(2))

ans = 2

target=[1 3];

find(comb_mat(:,1)==target(1) & comb_mat(:,2)==target(2))

ans = 3

target=[12 13];

find(comb_mat(:,1)==target(1) & comb_mat(:,2)==target(2)) % find will return empty if not found

ans = 0×1 empty double column vector

comb={1,2;3,4;1,3;1,2};

comb_mat=cell2mat(comb);

target=[1 2];

find(comb_mat(:,1)==target(1) & comb_mat(:,2)==target(2)) % find will return both indices if multiple results are found

ans = 2×1

1 4

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Pietro Fedrizzi 2021-10-22

Thank you very much! This example works great with my code, for the only exception that in my work 'target' is an array that I can decide, so it works just fine.

Thank you again for your time and your help!

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