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Sort the array by template

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I have two arrays A1 and B1 in which elements correspond:
A1 = [a1 a2 a3 a4 a5];
B1 = [b1 b2 b3 b4 b5];
then I change order of elements of the first array anyhow (they are all unique), for exaple like this:
A2 = [a4 a1 a3 a5 a2];
The question is how to get array B2 sorted in the same way? It should be
B2 = [b4 b1 b3 b5 b2];
I tried to write function which is:
B2 = zeros(length(B1),1);
for i = 1:length(B2)
ind = find( A1 == A2(i) );
B2(i) = B1(ind);
end
but as it uses for loops speed is not fast. Maybe there is a way to do it by using MatLab builtin functions?

Accepted Answer

Ameer Hamza
Ameer Hamza on 23 May 2018
Edited: Ameer Hamza on 23 May 2018
For a generalized matrix a1 and a2, you can use the following code
[~,index] = ismember(a2', a1', 'row');
b2 = b1(index)
This will work on R2016b and later.
  8 Comments
Ameer Hamza
Ameer Hamza on 23 May 2018
You will get hold of such solution once you start to develop some intuition about these frequently used MATLAB functions. Of course, that comes with time, experience and reading a lot of documentation :)

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More Answers (1)

sloppydisk
sloppydisk on 23 May 2018
a1 = [1 4 2 5 7];
b1 = 1:5;
mySecretOrder = [1 3 2 5 4];
a2 = a1(mySecretOrder);
[~, order] = ismember(a2, a1)
b1 = b1(order)
  2 Comments
sloppydisk
sloppydisk on 23 May 2018
Please see Ameer's answer.

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