flink datastream reduce

[rimin515]

Hi,      in flink,the datastream have reduce Transformations,but the result do 
not satisfy for me,    for example,    val pairs2 = 
env.fromCollection((Array(("a", Map(3->"rt")),("a", Map(4->"yt")),("b", 
Map(5->"dfs")))))    val re= 
pairs2.keyBy(0).reduce((x1,x2)=>(x1._1,x2._2++x1._2))    re.map{x=>         
println(x)          x    }
   the result are,     (a,Map(3 -> rt))     (a,Map(3 -> rt, 4 -> yt))     
(b,Map(5 -> dfs))
   but i want to get ,     (a,Map(3 -> rt, 4 -> yt))     (b,Map(5 -> dfs))
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