Logical Indexing returns error

Hi,

I'm trying to extract a two column vector from another two column vector using a logical statement.

For example, if column one contains x values and column two the corresponding y values, I want to create another matrix that contains only the x and y values when x is equal to a particular number. Here's the code I've used:

extracted_data=initial_data(initial_data==0,:);

This seems to work for some small test matrices. However, when I try to scale it up to extracting data from a vector with 64516 rows, I get the following error:

??? Index exceeds matrix dimensions.

Any ideas how I can avoid this? I've achieved the result I want using a loop and "if" statements, but this is SLOW!

Many thanks in advance,

T

Answer 1

[Fangjun Jiang]

It is not the number of rows. Your code won't work for nx2 array. You need to do this:

initial_data=rand(10,2);
extracted_data=initial_data(initial_data(:,1)<0.5,:)

Also, pay attention to "==0" if your data is floating point.