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

Question

Emerson De Souza 2012-10-15

0
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https://ww2.mathworks.cn/matlabcentral/answers/50812-how-to-construct-an-array-from-two-arrays-of-different-sizes-using-conditional-replacement-of-eleme

Hi, I have two arrays A and B as below

A=load('A.txt');
B=load('B.txt');

where

and

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=
4
NaN
10
NaN
NaN
15
NaN
17
59
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

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Andrei Bobrov 2012-10-25

在 MATLAB Online 中打开

A=[
1
2
3
4
5
6
7
8
9
10],
B=[
1  4
3  10
6.5  15
8  17
7.4     47
9  59]
out = [A, nan(numel(A),1)]
[a,b] = ismember(A,B(:,1))
out(a,2) = B(b(a),2)

Emerson De Souza 2012-10-25

Thank you Andrei,

these command lines are exactly what I need for general situations.

Emerson

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Answer 1

Azzi Abdelmalek 2012-10-15

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/50812-how-to-construct-an-array-from-two-arrays-of-different-sizes-using-conditional-replacement-of-eleme#answer_61986

编辑：Azzi Abdelmalek 2012-10-15

在 MATLAB Online 中打开

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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Matt Fig 2012-10-25

Give an example A and B that actually cover the type of data you will be encountering (this is what you should have done when you asked the first time!). Make sure your two example arrays cover all aspects of the real data...

Emerson De Souza 2012-10-25

Hi Matt Fig,

I absolutely agree with you, I should have thought more in detail before asking. Now reformulating the problem:

1)A and B are arrays with arbitrary number of rows and columns. Their values are elements of Real Numbers (exclude only complex numbers).

2)The array C is constructed as follows:

(i) The first column of C is identical with the first column of A,

(ii) The second column of C is initially filled with NaN,

(iii) Whenever there is a match between one element of the first column of A with one element of the first column of B, then the element of the second column of C equals the value of the element of the second column of B.

Fortunately, Andrei understood between my lines above and fixed the problem. Thank you anyways for your attention

Emerson

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