create a new matrix with elements from different sized matrices

Question

Sumedh Kulkarni 2018-1-26

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编辑： Sumedh Kulkarni 2018-2-1

The aim is to create a matrix (C_n) from two different matrices (M) and (t_e1) using a equality condition. I am trying to use the following code to do this. However,it gives me output as a matrix with zeros.

C_n=zeros(length(M),length(int));
for i= 1:length(int)                   %%length(int)=96
    for j=1:length(M)                  %%length(M)=300
        if M(j,i)==t_e1(j,1)           %%t_e1 is of size 300*2 and M is 300*96
            C_n(j,i)=t_e1(j,2);        %%Want to check each element of M that equals (j,1)th element of t_e1
                                       %%if true, replace each element of C_n by (j,2)th element of t_e1
             end
    end
end

What am I doing wrong in the above code?? Also, is there a better way to do get the required output (not using loops)?

Thank you!

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Answer 1

Youssef Khmou 2018-1-26

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编辑：Walter Roberson 2018-1-26

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By computing the difference between the two matrices A and B, find the indexes of the entries that equal zero and replace the entries of matrix C with the inputs of the indexes:

example:

A=round(100*rand(4));
B=round(100*rand(4));
T=A-B;     
C=zeros(size(A)); 
[a,b]=find(T==0);
C(a,b)=A(a,b);

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Sumedh Kulkarni 2018-1-26

I guess for this solution, matrix dimensions must be same. But in my case, they are not. One is 300*96 and the other is 300*2. I can`t compute difference between them. Also, I don`t want to find elements that equal 0, but the elements that are equal to other matrix`s 1st column.

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Answer 2

Domanic 2018-1-26

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https://ww2.mathworks.cn/matlabcentral/answers/379054-create-a-new-matrix-with-elements-from-different-sized-matrices#answer_301887

编辑：Domanic 2018-1-26

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I think the original code you had was correct, Sumedh. A minimum working example would be helpful, though. Try the following, which computes your loops on one line using logical vectors.

%%Set up example matrices
int = randi([0 3],[96 1]);
M=randi([0 3],[300 96]);
t_e1 = randi([0 3],[300, 2]);
%%Compute C_n
C_n = t_e1(:,2).*(M==t_e1(:,1));

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Sumedh Kulkarni 2018-2-1

在 MATLAB Online 中打开

Dominac, this doesnt work either. I tried to use the example you provided, which works quite well. But for me, i think the elements of Matrix M have same values in some columns. Maybe that`s the reason? It looks something like this:

12  20  20  39
13  23  36  94
20  36  39  124
23  39  49  200
36  49  94  226
39  57  106  275
49  94  110  0
57  106  124  0
88  110  137  0
94  124  200  0
102  137  201  0
106  141  226  0
110  200  275  0
114  201  0  0

and t_e1 looks like this:

Basically, M(1,1) is t_e1(9,1) and I want element corresponding to t_e(9,1), which is t_e1(9,2) in the new matrix. This needs to be done for each element in matrix M.

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