排序的地图在groovy [英] Sorted maps in groovy

问题描述

我有兴趣在groovy中使用排序的地图（gremlin是图形数据库的DSL）。

I am interested in using a sorted map in groovy (with gremlin which is a DSL for graph databases).

我已经看过这个博客在排序地图上，但我仍然有点困惑。

I have looked at this blog post on sorted maps here, but I am still a bit confused.

• 如何排序地图声明？是否与地图的标准方式有所不同？

使用排序地图，是插入到列表中的项目将按照插入的顺序？或者在排序地图中的项目排序之前，我必须运行 sort {} ？

When using a sorted map, are items inserted into the list going to be in the order they are inserted? Or will I have to run sort{} before the items in the sorted map are sorted?

推荐答案

如果您只是声明这样的地图：

If you just declare a map like so:

def m = [:]

然后，您可以看到Groovy默认使用 LinkedHashMap

Then, you can see Groovy by default makes a LinkedHashMap

assert m.getClass().name == 'java.util.LinkedHashMap'

如果您查看 LinkedHashMap的文档它说：

哈希表和链接列表实现的Map界面，具有可预测的迭代顺序。该实现与HashMap不同之处在于它保持双向链接列表的所有条目。此链接列表定义了迭代排序，通常是将键插入到地图（插入顺序）中的顺序。

Hash table and linked list implementation of the Map interface, with predictable iteration order. This implementation differs from HashMap in that it maintains a doubly-linked list running through all of its entries. This linked list defines the iteration ordering, which is normally the order in which keys were inserted into the map (insertion-order).

所以 LinkedHashMap 有一个订单，您可以通过调用 sort

So LinkedHashMap has an order, and you can affect that order in Groovy by calling sort

def m = [ b:1, a:2 ]

// Sort by descending value
m = m.sort { -it.value }

println m // prints [a:2, b:1]

如果要自然排序键，则可以使用Java的排序映射之一，例如 TreeMap

If you want natural ordering of the keys, then you can use one of Java's sorted maps, such as TreeMap

如果您想在Groovy中使用，可以执行以下操作：

To Say you want to use this in Groovy, you can do:

// def tm = [ tim_yates:1, F21:2 ] as TreeMap // works as well
TreeMap tm = [ tim_yates:1, F21:2 ]

然后打印这个，你可以看到它是按键排序的：

Then printing this, you can see it is ordered by the keys:

println map // prints [F21:b, tim_yates:a]

A TreeMap 将在添加密钥时维护顺序。当您添加新值时， LinkedHashMap 将不会自动保持排序。

A TreeMap will maintain order as you add keys. A LinkedHashMap will not automatically remain sorted when you add new values.

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