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Stefano Lombardi
Stefano Lombardi

Reputation: 1591

Selecting rows whose first column value appears at least once in a list

Suppose that:

A = [1,22,33; 2,44,55; 2,66,77]
id = [2 3 5]

I am trying to select all the matrix A rows if the value of their first column appears in id at least once, without using a loop.

Hence, starting from:

A =

 1    22    33
 2    44    55
 2    66    77

in this example I would like to get the following:

2    44    55
2    66    77

what is the easier way to do this? Many thanks.

Upvotes: 2

Views: 32

Answers (1)

Luis Mendo
Luis Mendo

Reputation: 112749

Use ismember to create a logical index that will select the rows:

A(ismember(A(:,1), id),:)

Alternatively, you can use any and bsxfun(@eq, ...) instead of ismember:

A(any(bsxfun(@eq, A(:,1).', id(:)), 1), :)

Or, starting at Matlab version R2016b, you can replace bsxfun(@eq, ...) by just == thanks to implicit singleton expansion:

A(any(A(:,1).'==id(:), 1), :)

Upvotes: 4

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