map，reduce模式

map(return otherObj =func(obj)) obj -> objmap

reduce(return obj = func(obj,obj))

filter(obj)

groupByKey(key,obj) = return (key,list(obj) func(key,obj)

groupByVal(obj,val) = return (val,list(obj) func(obj,val)

obj = map(obj)

obj = reduce(obj,obj)