code: function transform( data ) {
  		var qValues;
  
  		// Convert a comma delimited string into an array:
  		data = JSON.parse( '[' + data + ']' );
  
  		// Compute the quartiles:
  		qValues = quartiles( data );
  
  		// Return the interquartile range:
  		return qValues[1] - qValues[0];
  	}
docs: FUNCTIONS // 
  FUNCTION: transform( data )
  Defines the data transformation.
  
  @private
  @param {number} data - numeric stream data
  @returns {number} transformed data