[英]Scala flatten nested map
I have a nested Map like this one: 我有一个像这样的嵌套Map:
Map(1 -> Map(2 -> 3.0, 4 -> 5.0), 6 -> Map(7 -> 8.0))
I would like to 'flatten' it in a way such that the keys of the outer and inner maps are paired, ie for the example above: 我希望以一种方式“展平”它,使得外部和内部地图的键配对,即对于上面的示例:
Seq((1,2),(1,4),(6,7))
what is an elegant way to do this? 这是一种优雅的方式吗?
val m = Map(1 -> Map(2 -> 3.0, 4 -> 5.0), 6 -> Map(7 -> 8.0))
m.toSeq.flatMap({case (k, v) => v.keys.map((k,_))})
With for-comprehension: 理解:
val m = Map(1 -> Map(2 -> 3.0, 4 -> 5.0), 6 -> Map(7 -> 8.0))
scala> for((k1, v1) <- m.toSeq; k2 <- v1.keys) yield (k1, k2)
res4: Seq[(Int, Int)] = ArrayBuffer((1,2), (1,4), (6,7))
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