Remove the rows/columns with single values of a matrix
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Hello,
I have a matrix quite big (A < 23 x 250000 >). I want to evaluate the first row A(1,:) and eliminate the columns where there are values only repeated once. The number in this first row is an integer and always is increasing.
Lets say:
B = [1 1 3 5 5 5 7 9 9
0.1 0.5 0.2 0.4 0.3 0.9 0.1 0.6 0.5]
The result should be:
B = [1 1 5 5 5 9 9
0.1 0.5 0.4 0.3 0.9 0.6 0.5]
I know how to do it with for and if statements but I think it won't be efficient because the size of the matrix.
Many thanks!
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Dani Tormo
am 28 Nov. 2012
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per isakson
am 28 Nov. 2012
Bearbeitet: per isakson
am 28 Nov. 2012
A start:
B = [1 1 3 5 5 5 7 9 9
0.1 0.5 0.2 0.4 0.3 0.9 0.1 0.6 0.5];
[ uniqueB, ix ] = unique( B(1,:) );
sB = B(1,:);
sB( ix ) = [];
singleB = setdiff( uniqueB, sB );
[ ~, ixm ] = ismember( singleB, B(1,:) );
B( :, ixm ) = []
prints
B =
1.0000 1.0000 5.0000 5.0000 5.0000 9.0000 9.0000
0.1000 0.5000 0.4000 0.3000 0.9000 0.6000 0.5000
>>
your turn.
I'm wouldn't be surprise if the for-loop is faster :)
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