Converting a the result vector from logical indexing into a matrix possible or unnescesary?

Question

Daniel 2013-12-4

评论： Daniel 2013-12-7

Hello everyone,

I need to extract rows of a matrix with a certain value in one column. At the moment I am using logical indexing i this way:

c=A(:,2)==3; T=A([c,c,c,c]);

The problem I have is that T is a vector, with the columns added end to end, but I need it as a matrix.

Does Matlab provide an easy way to convert such a vector to a matrix or is there another easy way to extract the rows into a matrix?

Thank you everybody.

Answer 1

Andrei Bobrov 2013-12-4

T = A(A(:,2) == 3,:);

Daniel 2013-12-7

Sorry doesn't work. I get

T =

Empty matrix: 0-by-10

as a result.

Thanks anyway.

Daniel 2013-12-7

Works like a charm, if i use the correct data. Thanks again.

Answer 2

Jos (10584) 2013-12-7

Often, you get some insight when you remove the semi-colons

A = [1 2 3 4 ; 11 3 13 14 ;21 22 23 24 ; 41 3 43 44] % example data
c = A(:,2)==3
T = A(c,:)

if T is empty, there are simply no rows that have a value of 3 in the second column.

Daniel 2013-12-7

Sorry was using the wrong matrix. The first answer works just fine. To much data and I lost track of what is what. Thanks to both of you.