combinations, nchoosek or similar function nx2 array

I have data points (x and y) that I am using to fit a curve. I need to find out which 4 give me the best fit.

So I need a way to represent the 'x y' pair together or find a function that can give me combinations of each row.

At the moment I get every combinations of x values and then re-pair then with the y values after, very inefficient

[Matt Tearle]

I'm having a hard time interpreting the question. "... which 4 give me the best fit" -- which 4 what? (x,y) pairs? Are you fitting a curve to four points, so you want to take every 4-point combination from the n data points that you have? Can you provide a simple example? You have x and y in what form? n-element vectors? So something like

x y

0 0

1 1

2 4

3 9

4 16

5 25

6 36

So now what are you looking for from this?