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How to add 1 matrix to another matrix ?

Asked by Ahsan Abbas on 27 Apr 2016
Latest activity Commented on by Ahsan Abbas on 30 Apr 2016
I have 2 matrices with different size as show below and just want to concatenate both of them. I know 2nd matrix have 1st 6 columns entries that are lying in b/w 1st matrix somewhere, so now i just want to add last 2 column values to 1st matrix of there corresponding rows of 1st matrix. Can someone help me how to write syntax for this ?

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The result will be single matrix having entries of both matrices.
This is not clear. post the result to make it clear
x = [1 2 3; 4 5 6; 7 8 9; 10 11 12]; y = [4 5 6 12 15; 10 11 12 25 52]; result would be like z = [1 2 3 0 0; 4 5 6 12 15; 7 8 9 0 0; 10 11 12 25 52];

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2 Answers

Answer by Star Strider
on 27 Apr 2016
Edited by Star Strider
on 27 Apr 2016
 Accepted Answer

One approach, taking advantage of the fact that both of your matrices are sorted by the first column:
M1 = sortrows(rand(15, 4), 1); % Create 1st Matrix & Sort By Column #1
M2 = [M1(1:5:end,:) rand(3,2)]; % Create 2nd Matrix & Add Columns #5 & #6
idx = find(ismember(M1(:,1), M2(:,1))); % Find Indices Of Matching Column #1 Entries
M1 = [M1 zeros(size(M1,1),2)]; % Add Zeros To End Of ‘M1’
M1(idx,5:6) = M2(:,5:6); % Fill Columns #5 & #6 With Same Values From ‘M2’
Since you are dealing with floating-point numbers, if you have R2015a or later, you would likely best use ismembertol instead of ismember to guarantee that your data match.

  2 Comments

Thanks Star Strider for helping, i am using matlab 2013b so ismember is the only option.
My pleasure.
I’m hoping that your matrix entries are exact, so that ismember will work. If not, we will work on a way to use a tolerance with it. Rounding the first column of each matrix to a particular number of decimal places first would likely be easiest.

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Answer by Azzi Abdelmalek
on 27 Apr 2016

[n1,m1]=size(x)
[n2,m2]=size(y)
z=zeros(n1,m2)
idx=ismember(x,y(:,1:m1),'rows')
z(idx,:)=y
z(~idx,1:m1)=x(~idx,:)

  1 Comment

Thank you Azzi for your response.

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