function copyBy( x, N, out, stride, offset, clbk, thisArg ) {
	var i;
	for ( i = 0; i < N; i++ ) {
		out[ offset ] = clbk.call( thisArg, x[ i ], [ i ], x );
		offset += stride;
	}
}
Copies a specified number of array elements to a provided array according to a callback function.

@private
@param {Array} x - input array
@param {NonNegativeInteger} N - number of elements to copy
@param {Collection} out - output array
@param {integer} stride - output array stride
@param {NonNegativeInteger} offset - output array offset
@param {Function} clbk - callback function
@param {*} [thisArg] - callback execution context

@example
function scale( v ) {
    return v * 2;
}

var x = [ 1, 2, 3, 4 ];

var out = [ 0, 0, 0 ];
copyBy( x, 3, out, 1, 0, scale );

var o = out;
// returns [ 2, 4, 6 ]