code: def groupByNode(requestContext, seriesList, nodeNum, callback):
      
      return groupByNodes(requestContext, seriesList, callback, nodeNum)
docs: Takes a serieslist and maps a callback to subgroups within as defined by a
      common node.
  
      Example::
  
          &target=groupByNode(ganglia.by-function.*.*.cpu.load5,2,"sumSeries")
  
      Would return multiple series which are each the result of applying the
      "sumSeries" function to groups joined on the second node (0 indexed)
      resulting in a list of targets like::
  
          sumSeries(ganglia.by-function.server1.*.cpu.load5),
          sumSeries(ganglia.by-function.server2.*.cpu.load5),...