MATLAB: How to construct an array from two arrays of different sizes using conditional replacement of elements

arraysfor loopif statementMATLAB

Hi, I have two arrays A and B as below
A=load('A.txt');
B=load('B.txt');
where
A=
1
2
3
4
5
6
7
8
9
10
and
B=
1  4
3  10
6  15
8  17
9  59
Goal: I want to construct an array C with the same length as A. The elements of C equals the elements of the second column of B if the elements of the first column of A and the elements of the first column of B are equal. Otherwise, the elements of C is not available (NaN)
Thus, C should look like below:
C=
1  4
2  NaN
3  10
4  NaN
5  NaN
6  15
7  NaN
8  17
9  59
10  NaN
I tried the following command lines:
C=zeros(size(A));
for i=1:numel(A);
    for j=1:numel(B);
if  A(i)=B(j);
    C(i)=B(j,2);       
else
    C(i) = NaN;
end;end;
but had no success yet. I wonder if someone could help me to correct the mistakes I have done or suggest something else that works.
I thank you in advance for you help
Emerson

Best Answer

C=nan(numel(A),1)
for k=find(ismember(A,B(:,1))==1)
  C(k)=B(find(B(:,1)==A(k)),2)
end
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