Function that will select one of two data sets

I am trying to set up a function that will pick one of two data sets. If a set parameter is postive I want this to be from the first data set. If a set parameter is negative I want the second data set used. Here is basic structure of what I have so far but I do not think I have the logic correct.

function [ x y ] = donor( set_ind )

global vols sets

ind_first   = sets.set_dat(set_ind).first;
ind_second   = sets.set_dat(set_ind).second;

if z > 0
    [ x y ] = ind_first;
elseif z < 0
    [ x y ] = ind_second;
end
end

Answer 1

[Image Analyst]

Try

function [xy] = donor(setIndex)
global sets
if rand(1) > 0.5
    xy = sets.set_dat(setIndex).first;
else
    xy = sets.set_dat(setIndex).second;
end
end