Combining Logical Indexes

I have two logical Indexes that I need to reference with my large Matrix of data before performingons. One Index (MyDates) is 1x693 and the other (MyTickers) is 589x1. I need to combine the two Indexes into one large 589x693 logical index. How do I go about oing that?

Thanks, Brian

Answer 1

[Fangjun Jiang]

What is the operation, and, or, plus, minus?

bsxfun(@and,MyTickers,MyDates)

[Brian]

It would be times I believe. For example

Idx1 = [1 0 1]

Idx2 = [1; 1; 0]

Intsection should yield

Idx3 = [1 0 1; 1 0 1; 0 0 0]

[Fangjun Jiang]

Then @and is what you need!

[Sean de Wolski]

Fangjun is correct! times would work, but it's slightly slower since ML has to do a multiplication instead of a logical operation.

Answer 2

[Brian]

Excellent that works great. I used the syntax below.

Idx3 = bsxfun(@and,index2,index1)

So now Idx3 is a 5x5 logical matrix. However, when I try to apply this logical matrix to my 5x5 matrix (MyRtn) in the format MyRtn2 = MyRtn(Idx3) I end up with MyRtn2 being a 9x1 matrix??? Why would that be happening?

[Walter Roberson]

What shape were you expecting? When you extract arbitrary elements out of a matrix, there is no way for MATLAB to leave "hole" that preserve any original existing shape.

[Fangjun Jiang]

That is expected. If you want to keep the shape of the original matrix, you need fill it with something depending on your need. For example,

a=magic(3);

b=logical([1 1 0;0 1 0;0 1 0]);

a(~b)=nan;