Assigning element of another array into another array based on index

Question

Mich 2014-10-29

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评论： Guillaume 2018-5-16

I've stored the index of the elements of interest in an array, B, and would like to use the values in B to obtain the values of the elements in another array, A, at positions indicated in B.

e.g.

    A = [5 4 4 5 6 6 8 5 8 5 14 11 3 2 4 5];
    B = [1 2 4 8 10 12 16];
    for i = 1: length(B)
        if (A(B(i))== 5)
        idx = [idx,i];
    end
    end

form my understanding, i should be able to get idx = 1 4 8 10 16 However, what i am getting is idx = 1 5 10 15

I'm not sure what is the problem as the logic of the code seems right to me.

can i also check what is the difference between array and matrix?

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Answer 1

Matt J 2014-10-29

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编辑：Matt J 2014-10-29

You don't really need a loop at all and can do the whole thing in one line,

idx=B(A(B)==5)

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Matt J 2014-10-29

编辑：Matt J 2014-10-29

I never proposed anything that looks like B(...)== 5. The expression I wrote is B( A(B)==5 ).

I tested my proposal on your example data and it worked fine for me. So, whatever's causing your error, it's coming from something unposted.

Mich 2014-10-29

编辑：Mich 2014-10-29

hey i apologise for my mistake. my original code was way more complex and i simplified it to this, but the same variables were used, thus resulting in my initial confusion when i tried out your suggestion. i tried your suggestion again and it works! thanks alot!!

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Answer 2

vimala victor 2018-5-16

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hi, i have one array RL=[1 13 11 14 25 37 53 29 75 81 66 10 98 15 33 44 77 88 20 49 1 3 4 2 5 1 2 2 3 4 2 1 5 2 3 1 2 4 3 3]; That is first row defines the index values and second row is the values of corresponding index.(Eg.for index value 1 the value is 1,index value 13 the value is 3...) and IM= 44 14 98 88 20 13 11 37 77 25 81 20; How can i extract the corresponding IM indexing Values from RL using indexing. please ,can anyone help me to clarify my doubt with how to define in matlab coding