Find elements of an array in another array
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Hello,
Let's say I have 2 arrays of double, call then A and B. If both have unique entries and I want to find the position of each element of A in array B I can do:
[~, pos] = ismember(A,B);
What if the elements of A show up multiple times in B and I want to get the first time they show up or the last time they show up? I know I can do
pos = zeros(length(A),1);
for k = 1:length(A)
pos(k) = find(B == A(k),1,'first');
end;
But is there a better, more efficient way of doing it? For loops are not exactly in the spirit of Matlab as far as I know.
Thanks, Alex
1 commentaire
Azzi Abdelmalek
le 20 Sep 2013
If
a=[1 2 3 4 5 6 7]
b=[12 13 2 4 3 2 4 2 25]
what is the expected result?
Réponse acceptée
Azzi Abdelmalek
le 20 Sep 2013
Modifié(e) : Azzi Abdelmalek
le 20 Sep 2013
Maybe in your case, all element in A are present in B
A=[1 2 3 4 5 6 7]
B=[12 13 2 4 3 2 4 2 25 1 6 7 5]
pos=arrayfun(@(x) find(B==x,1),A)
2 commentaires
Azzi Abdelmalek
le 20 Sep 2013
Modifié(e) : Azzi Abdelmalek
le 20 Sep 2013
Use in the loop
id=find(B==A(k),2)
id=id(2)
Plus de réponses (1)
Azzi Abdelmalek
le 20 Sep 2013
Modifié(e) : Azzi Abdelmalek
le 20 Sep 2013
I prefer this one. It should be much faster
A=[1 2 3 4 5 6 7]
B=[12 13 2 4 3 2 4 2 25 1 6 7 5];
[ii,jj]=unique(B,'stable');
n=numel(A);
pos = zeros(n,1);
for k = 1:n
pos(k)=jj(find(ii == A(k)));
end;
2 commentaires
Azzi Abdelmalek
le 20 Sep 2013
Modifié(e) : Azzi Abdelmalek
le 20 Sep 2013
This answer is more efficient then the first one
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