如何将Java对象列表转换为2D数组? [英] How to convert java list of objects to 2D array?
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问题描述
是否有一种简单的方法可以在Java 8中使用lambda进行转换
Is there an easy way to use lambda in java 8 to convert
从该对象开始:
"coords" : [ {
"x" : -73.72573187081096,
"y" : 40.71033050649526
}, {
"x" : -73.724263,
"y" : 40.709908}
]
此对象:
"coordinates":[
[
[
-73.72573187081096,
40.71033050649526
],
[
-73.724263,
40.709908
]]
我尝试使用 transform()
函数,但是如何从列表转换为2D数组?
I try to use transform()
function but how can i transform from list to 2D array ?
这是我的尝试,但我遇到了一个错误:
here is my try, but i got an error:
coordinates =
Lists.newArrayList(
Lists.newArrayList(
Lists.newArrayList(
coords.stream()
.map( item -> Lists.newArrayList(ImmutableList.of(item.x, item.y))))));
推荐答案
不是100%知道您要问什么,但我会尝试一下.假设您有一个积分列表...
Not 100% sure what you are asking, but I'll give it a try. Assuming you have a list of Points...
List<Point2D> points = Arrays.asList(new Point2D.Double(12., 34.),
new Point2D.Double(56., 78.));
...您可以将该列表转换为2D数组,如下所示:
... you can turn that list into a 2D-array like this:
double[][] array = points.stream()
.map(p -> new double[] {p.getX(), p.getY()})
.toArray(double[][]::new);
...或这样的嵌套列表:
... or into a nested list like this:
List<List<Double>> list = points.stream()
.map(p -> Arrays.asList(p.getX(), p.getY()))
.collect(Collectors.toList());
在两种情况下,结果分别看起来像这样 [[12.0,34.0],[56.0,78.0]]
,作为数组或列表.
In both cases, the result looks like this [[12.0, 34.0], [56.0, 78.0]]
, as an array or a list, respectively.
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