function indexed( x ) {
	var n;
	var i;

	n = 0;
	for ( i = 0; i < x.length; i++ ) {
		if ( x[ i ] ) {
			n += 1;
		}
	}
	return n;
}
Counts the number of truthy values in an indexed array.

@private
@param {Collection} x - input array
@returns {NonNegativeInteger} number of truthy values

@example
var x = [ 0, 1, 0, 1 ];

var n = indexed( x );
// returns 2