You've got it
From the Official Command Reference:
array select index
Operand types:
array: Array
index: Number
Type of returned value:
Any Value
Description:
select index element of array, index 0 denotes the first element, 1 the second
Example:
[1, 2, 3] select 1 , result is 2
So basically, if you've got an array... say:
[a, b, c]
Then
array select 0 would be: a
array select 1 would be: b
and
array select 2 would be: c
(Just note that the numbering starts from 0, not 1).
So using that in the style of co-ordinates, we've got:
[x, y, z]
So select 0 is your East-West co-ord, select 1 your North-South co-ord, and select 2 your Vertical component.
Hope that helps you out a bit