# How to select rows of matrix based on other matrix column?

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Emma Kuttler le 22 Mar 2022
Modifié(e) : Voss le 24 Mar 2022
Hi, I have a single column matrix called "nodes" and a larger matrix with many columns called "arcs". If values from "nodes" appear in both of the first two columns of "arcs", I want to return that row from "arcs" and put it in a new matrix. If one or both of the values in the first two columns of "arcs" does not appear in "nodes", do not return that row.
For example, if these are the matrices nodes and arcs, I want to produce "arcssmall"
nodes = [1
2
4
6
9
11]
arcs = [1 2 0 1 4
1 3 9 8 7
2 1 8 3 0.5
4 11 9 0 0
6 9 5 5 5
5 6 1 2 3
9 1 0 0 0
7 8 6 7 7]
arcssmall = [1 2 0 1 4
2 1 8 3 0.5
4 11 9 0 0
6 9 5 5 5
9 1 0 0 0]
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### Réponses (1)

Voss le 22 Mar 2022
nodes = [1
2
4
6
9
11];
arcs = [1 2 0 1 4
1 3 9 8 7
2 1 8 3 0.5
4 11 9 0 0
6 9 5 5 5
5 6 1 2 3
9 1 0 0 0
7 8 6 7 7];
arcssmall = arcs(all(ismember(arcs(:,[1 2]),nodes),2),:)
arcssmall = 5×5
1.0000 2.0000 0 1.0000 4.0000 2.0000 1.0000 8.0000 3.0000 0.5000 4.0000 11.0000 9.0000 0 0 6.0000 9.0000 5.0000 5.0000 5.0000 9.0000 1.0000 0 0 0
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Emma Kuttler le 24 Mar 2022
Thanks! How would I change the script so that I was only checking in the first column of arcs to see if there was a match for a value in nodes?
Voss le 24 Mar 2022
Modifié(e) : Voss le 24 Mar 2022
nodes = [1
2
4
6
9
11];
arcs = [1 2 0 1 4
1 3 9 8 7
2 1 8 3 0.5
4 11 9 0 0
6 9 5 5 5
5 6 1 2 3
9 1 0 0 0
7 8 6 7 7];
% arcssmall = arcs(all(ismember(arcs(:,[1 2]),nodes),2),:)
arcssmall = arcs(ismember(arcs(:,1),nodes),:) % change [1 2] to just 1, and no need to use all(__,2) in this case
arcssmall = 6×5
1.0000 2.0000 0 1.0000 4.0000 1.0000 3.0000 9.0000 8.0000 7.0000 2.0000 1.0000 8.0000 3.0000 0.5000 4.0000 11.0000 9.0000 0 0 6.0000 9.0000 5.0000 5.0000 5.0000 9.0000 1.0000 0 0 0

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