Find the indices of one variable in another one avoiding NaNs

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Daria Ivanchenko 2020-11-3

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https://ww2.mathworks.cn/matlabcentral/answers/635219-find-the-indices-of-one-variable-in-another-one-avoiding-nans

评论： Daria Ivanchenko 2020-11-4

Hi!

I have two matrices, A and B, they have the same number of rows and different number of columns. Matrix A is just some numbers, matrix B is the indices. Both matrices have different amout of NaNs in the end.

I want to find the number in matrix A that matches the index in the matrix B (using the simple C = B(A)). But it doesn't work with NaNs inside the matrices. Is there some other way to do it?

A = [1 2 3 7 8; 1 5 3 NaN NaN; 1 9 3 6 NaN];
B = [2 4 5 NaN; 1 2 3 NaN NaN; 1 2 NaN NaN NaN];
C = B(A);
C = [2 7 8; 1 5 3; 1 9];

Thanks!

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Daria Ivanchenko 2020-11-3

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Regarding the sample, this one is correct:

A = [1 2 3 7 8; 1 5 3 NaN NaN; 1 9 3 6 NaN];
B = [2 4 5 NaN NaN; 1 2 3 NaN NaN; 1 2 NaN NaN NaN];
C = B(A);
C = [2 7 8; 1 5 3; 1 9];

Yeah, I missed one NaN, sorry.

Stephen23 2020-11-3

编辑：Stephen23 2020-11-3

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This is not a valid matrix, because the rows have different numbers of elements:

C = [2 7 8; 1 5 3; 1 9]; % NOT VALID

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Answer 1

Stephen23 2020-11-3

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https://ww2.mathworks.cn/matlabcentral/answers/635219-find-the-indices-of-one-variable-in-another-one-avoiding-nans#answer_533064

编辑：Stephen23 2020-11-3

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The C you showed in your example is not possible as it has different numbers of elements in each row, but you could put the data into a cell array:

>> A = [1 2 3 7 8; 1 5 3 NaN NaN; 1 9 3 6 NaN]
A =
     1     2     3     7     8
     1     5     3   NaN   NaN
     1     9     3     6   NaN
>> B = [2 4 5 NaN NaN; 1 2 3 NaN NaN; 1 2 NaN NaN NaN]
B =
     2     4     5   NaN   NaN
     1     2     3   NaN   NaN
     1     2   NaN   NaN   NaN
>> idx = ~isnan(B);
>> [idr,~] = find(idx);
>> idc = B(idx);
>> idy = sub2ind(size(A),idr,idc);
>> C = accumarray(idr,A(idy),[],@(v){v});
>> C{:}
ans =
   2
   7
   8
ans =
   1
   5
   3
ans =
   1
   9