使用stream来汇总存储在map中的数组中的所有值 [英] use stream to sum all values from array stored in map
问题描述
我有一张如下所示的地图:
I have a map which looks like this:
Map<String,String[]> urlFormEncoded = new HashMap<String,String[]>();
我希望将存储在String []数组中的所有值加总为double值
我试过这样的事情:
and I would like to sum all values stored in String[] arrays as a double value I tried something like this:
double requestAmount = urlFormEncoded.entrySet().stream().mapToDouble(k -> Arrays.stream(k.getValue()).).sum();
但遗憾的是我不知道如何将此String []转换为值:(
我想用stream和lambda表达式做这个
but unfortunately I don't know how to convert this String[] to value :( I would like to do this using streams and lambda expressions
推荐答案
第一步是转换每个 String []
作为 DoubleStream
。
The first step would be to convert each String[]
as a DoubleStream
.
Arrays.stream(arr).mapToDouble(Double::valueOf)
然后你必须 flatMap
获得单个 DoubleStream
的那些流将全部 double
值。
Then you have to flatMap
those streams to get a single DoubleStream
will all the double
values.
.flatMapToDouble(arr -> Arrays.stream(arr).mapToDouble(Double::valueOf))
所以你最终得到:
double requestAmount =
urlFormEncoded.values()
.stream()
.flatMapToDouble(arr -> Arrays.stream(arr).mapToDouble(Double::valueOf))
.sum();
请注意,如果您打算只处理值,则不需要使用 entrySet()
,您可以直接使用值()
。
Note that you don't need to use the entrySet()
if you plan to work only on the values, you can directly use values()
.
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