if only 1 value of y is pointed to by the same value of x, then you have a function.
if you also have only 1 value of x that points to the same value of y, then you have a 1 to 1 function.
if your re-orient your data in ascending values of x, you will get:
x y
-4 4
-2 5
-1 3
0 2
3 -3
5 1
you can see in this data that no 2 values of x are the same and no 2 values of y are the same.
therefore the data is a 1 to 1 function.
if it was not a function, you might have seen something like this:
x y
-2 4
-2 5
-1 3
0 2
3 -3
5 1
you can see that the -2 value of x points to more than one value of y.
that means it is not a function.
if it was a function, but not a 1 to 1 function, you might have seen something like this:
x y
-4 4
-2 4
-1 3
0 2
3 -3
5 1
you can see that the 4 value of y is pointed to by more than 1 value of x.
it is still a function because only one value of x points to the same value of y.
it is not a 1 to 1 function because more than 1 value of x points to the same value of y.
bottom line is that you have a 1 to 1 function.
here's a decent reference on the subject.
http://www.purplemath.com/modules/fcns.htm