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Poulomi
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Merging two dissimilar matrix based on common row element

Asked by Poulomi
on 4 Aug 2017
Latest activity Answered by Jan
on 5 Aug 2017
I have two arrays
A = 1 2.576
1 2.822
13 2.679
13 2.786
25 2.653
25 2.596
25 2.565
B= 1 nan
1 nan
1 nan
2 nan
2 nan
2 nan
.. nan
.. nan
13 nan
13 nan
13 nan
14 nan
14 nan
14 nan
.. nan
.. nan
20 nan
20 nan
20 nan
.. nan
.. nan
.. nan
25 nan
25 nan
25 nan
I have to create a third matrix C, which have all variables combined based on first column of B, while putting the values of A into it. The empty element, for which no values of A is available should be filled with nan. Desired output is matrix C.
C = 1 2.576
1 2.822
1 nan
2 nan
2 nan
2 nan
3 nan
3 nan
3 nan
4 nan
4 nan
4 nan
.. nan
.. nan
10 nan
10 nan
10 nan
13 2.679
13 2.786
14 nan
14 nan
14 nan
.. nan
.. nan
20 nan
20 nan
20 nan
25 2.653
25 2.596
25 2.565
I tried with intersect, however, it's not working for this case since the common column contains repeated values. Any help?

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2 Answers

Answer by Andrei Bobrov
on 4 Aug 2017
Edited by Andrei Bobrov
on 4 Aug 2017

A = [1 2.576
1 2.822
13 2.679
13 2.786
25 2.653
25 2.596
25 2.565];
B = [kron((1:25)',[1;1;1]),nan(25*3,1)];
C = B;
p = findgroups(A(:,1));
AA = [A(:,1),cell2mat(accumarray(p,1,[],@(x){(1:numel(x))'}))];
q = findgroups(B(:,1));
BB = [B(:,1), cell2mat(accumarray(q,1,[],@(x){(1:numel(x))'}))];
C(ismember(BB,AA,'rows'),2) = A(:,2);

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@Poulomi Ganguli: If this solves your problem, please accept the answer.

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Answer by Jan
on 5 Aug 2017

Or with simple loops:
C = B;
kC = 1;
nC = size(C, 1);
for iA = 1:size(A, 1)
a = A(iA, 1);
for iC = kC:nC
if C(iC, 1) == a
C(iC, 2) = A(iA, 2);
kC = iC + 1;
break; % Stop for iC loop
end
end
end

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