Splitting a list at a particular position

Question

Is it possible to split a list into two lists at a specific position? The main list is for example:

data={{xa,ya},{xb,yb},{xc,yc},...,{xz,yz}}. 

I want to split this list into two new lists:

data1={{xa,ya},{xb,yb},...,{xi,yi}} 

and

data2={{xj,yj},{xk,yk},...,{xz,yz}} 

at a specific y-value at position i. I was not successful in using Part. Maybe there is another possibility?

Answer 1

This can be accomplished easily using Part ([[ ]]) and Span (;;), as follows:

data = {{x1, y1}, {x2, y2}, {x3, y3}, {x4, y4}, {xz, yz}};
data[[;; 3]]
data[[4 ;;]]

(* ->
{{x1, y1}, {x2, y2}, {x3, y3}}
{{x4, y4}, {xz, yz}}
*)

Answer 2

Following up on J.M.'s suggestion,

m = 3;
data1 = Take[data, m]
data2 = Take[data, -(Length[data] - m)]

You might also obtain data2 as follows:

data2 = Complement[data, data1]

I'm uncertain whether the second approach would maintain order invariant if there are identical sublists.