function zip( x, y ) {
	var out;
	var i;
	if ( x.length !== y.length ) {
		throw new Error( format( 'invalid arguments. Must provide equal length array-like objects. x length: `%u`. y length: `%u`.', x.length, y.length ) );
	}
	out = new Array( x.length );
	for ( i = 0; i < x.length; i++ ) {
		out[ i ] = [ x[i], y[i] ];
	}
	return out;
}
Zips two arrays.

@private
@param {ArrayLike} x - x-values
@param {ArrayLike} y - y-values
@throws {Error} must provide equal length array-like objects
@returns {Array<Array>} zipped array