find where both matrices match

Hi,

I have matrix A and matrix B. The first column in both of them is a dates column where few observations and A and B coincide. I have created a matrix C where the first column in C is the dates of A and I want to put in the matrix the observations of B where the dates match.

I tried x0=find(ismember(B(:,1),A(:,1))==1); but how can I find the rows in C where i need to put B(x0,2:end)?

Answer 1

[Fangjun Jiang]

I am having a second thought. The first solution requires:

1. no duplicate dates in A alone and in B alone.
2. the dates in A and B shall be sorted and in the same order (ascending or descending). If not, the results will be incorrect. Un-comment the line to see the effect.

A=[1:10;1:10]';
B=[2:2:20;20:20:200]';
%B=B(end:-1:1,:);
C=nan(size(A));
C(:,1)=A(:,1);
IndexA=ismember(A(:,1),B(:,1));
IndexB=ismember(B(:,1),A(:,1));
C(IndexA,2)=B(IndexB,2);

A better solution is below. It still requires no duplicate dates which should be the case based on the task.

A=[1:10;1:10]';
B=[2:2:20;20:20:200]';
B=B(end:-1:1,:);
C=nan(size(A));
C(:,1)=A(:,1);
[Dummy,IndexA,IndexB]=intersect(A(:,1),B(:,1));
C(IndexA,2)=B(IndexB,2);

[Oleg Komarov]

[indexA, locB] = ismember(A(:,1),B(:,1));

C(IndexA,2) = B(locB,2);

[Fangjun Jiang]

Oleg, I thought it should work too. But it didn't. locB contains zeros. Could you try? Note it is 'IndexA', not 'indexA'.

[Fangjun Jiang]

Or could make it work this way.

[IndexA, locB] = ismember(A(:,1),B(:,1));

C(IndexA,2) = B(locB(IndexA),2);

[Oleg Komarov]

The zeros! I always do ismember(A, subset of A), that's why I forgot about zeros, but of course this implies that one is a subset.