How can I use one variable to extract specific observations from another variabel?

I have a variable (A) signalling to buy or sell another variable (B) (if A is negative; sell (positive; buy). What is the easiest way to extract all the "buys" and "sells" from variable B in different datasets (so I have one dataset "Buy" and one dataset "Sell") based on the information in A? For example if A is;

• -2
• -1
• 2
• 3

And B is;

• 5
• 10
• 8
• 4

I want to have an ouput of two datasets; "Buy" with 4 and 8, and "Sell" with 5 and 10.

Any help is much appreciated! Best wishes for the new year!

Answer 1

[Wayne King]

You can use logical indexing on A to select the appropriate elements of B

A = [-2 -1 2 3];
B = [5 10 8 4];

buyz = B(A>0);
sellz = B(A<0);

[Anders]

Thank you!