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

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Pietro Fedrizzi on 21 Oct 2021
Commented: Pietro Fedrizzi on 22 Oct 2021
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.
dpb on 22 Oct 2021
Just repeating the same unclear verbiage doesn't help -- SHOW us the input and corresponding output expected.

Dave B on 21 Oct 2021
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 = 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];
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
Pietro Fedrizzi on 22 Oct 2021
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.