code: function signum( y, x, clbk ) {
  	var len = x.length,
  		i;
  	for ( i = 0; i < len; i++ ) {
  		y[ i ] = SIGN( clbk( x[ i ], i ) );
  	}
  	return y;
  }
docs: SIGNUM FUNCTION // 
  FUNCTION: signum( out, arr, accessor )
  Evaluates the signum function for each array element using an accessor function.
  
  @param {Array} out - output array
  @param {Array} arr - input array
  @param {Function} accessor - accessor function for accessing array values
  @returns {Number[]} output array