How to compare two arrays and add elements to the first one

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Patrick Benz 2021-2-12

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评论： Patrick Benz 2021-2-12

I've got two arrays of different dimensions. The first is a 41x4 and the other one a 400000x4.

I would like to find those rows where the element in the first column in the same in both arrays and either add the entries from the last three columns to the first array or, if it is easier, write the whole row of the second array into a new array and proceed.

Is there an easier way to do this without two loops? Because I don't like to run through 400k elements 40 times.

As en example:

Array 1: 990 0 0 0
         991 0 0 0
Array 2: 991 5 7 3

What I want:

        990 0 0 0
        991 5 7 3    

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Answer 1

dpb 2021-2-12

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You were on the right track...

[LIA,LOCB]=ismember(A1(:,1),A2(:,1));         % find locations in respective arrays first column
A1(LIA,:)=A2(LOCB(LIA),:);                    % replace the matched rows in A1 with A2

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Patrick Benz 2021-2-12

thx, that is way faster than my method

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Answer 2

Patrick Benz 2021-2-12

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There are probably more elegant ways, I got what I wanted by using following code:

[LIA,LOCB]=ismember(elNum,node_Num)
Auswertung=zeros(length(LOCB),4)
for i=1:length(LOCB)
    index=LOCB(i,1)
    Auswertung(i,1)=node_Num(index,1);
    Auswertung(i,2)=node_Num(index,2);
    Auswertung(i,3)=node_Num(index,3);
    Auswertung(i,4)=node_Num(index,4);
end