[英]Java Sort a list based on another list
I have an ArrayList of the following type: 我有以下类型的ArrayList:
class Move
{
int from, to;
}
The from property always has a value. from属性始终具有一个值。 The to property will have -1 if it is not set. 如果未设置,则to属性的值为-1。 I have the following array: 我有以下数组:
int[][] history = new int[50][50];
where the dimensions correspond to the 'from' and 'to' of the move class. 尺寸对应于移动类别的“从”和“至”。 In my search function, and depending on certain conditions I need to do: 在搜索功能中,根据某些条件,我需要执行以下操作:
List<move> moves = board.getMoves();
for (int i = 0; i < moves.size(); i++)
history[move.from][move.to]++;
Because move.to could also be -1, should I increase the dimension of the 2d array 1 and then do: 因为move.to也可以是-1,所以我应该增加2d数组1的尺寸,然后执行以下操作:
history[move.from+1][move.to+]++;
Also, based on the above move list and history array, I need to sort the move list in descending order depending on the counter of the corresponding history index. 另外,基于上面的移动列表和历史记录数组,我需要根据相应历史记录索引的计数器以降序对移动列表进行排序。
Is this possible? 这可能吗?
您可以在Comparator的实现中使用Collections.sort(List,Comparator) ,它将按您希望的顺序进行排序。
Yes, you can make your comparator that uses the history array. 是的,您可以使您的比较器使用历史记录数组。 As an example, I sort my list of int according to an other array counts
. 例如,我根据其他数组counts
对我的int列表进行排序。
public static void main(String[] args) {
List<Integer> list = new ArrayList<>();
list.addAll(Arrays.asList(new Integer[]{0, 1, 2, 3, 4, 5}));
final int[] counts = new int[] {3, 4, 1, 7, 0, 1};
Collections.sort(list, new Comparator<Integer>() {
@Override
public int compare(Integer arg0, Integer arg1) {
return counts[arg1] - counts[arg0];
}
});
System.out.println(list);
}
Outputs: [3, 1, 0, 2, 5, 4]
输出: [3, 1, 0, 2, 5, 4]
3、1、0、2、5、4 [3, 1, 0, 2, 5, 4]
Your compare
would be something like: 您的compare
将类似于:
@Override
public int compare(Move move0, Move move2) {
return history[move1.from+1][move1.to] - history[move0.from+1][move0.to];
}
You can setup history as a HashMap or separate class to make this easier. 您可以将历史记录设置为HashMap或单独的类,以使其更容易。 But because you also like to be able to sort history based on frequency, I would recommend a History class: 但是,由于您还希望能够根据频率对历史记录进行排序,因此我建议您使用History类:
class Move {
int from, to;
@Override
public int hashCode() {
return from + (to * 100);
}
@Override
public boolean equals(Object o) {
return (o instanceof Move
&& ((Move) o).from == from
&& ((Move) o).to == to);
}
}
class History extends Move implements Comparable<History> {
int frequency;
public History(Move m) {
from = m.from;
to = m.to;
frequency = 1;
}
public void increment() {
frequency += 1;
}
public int compareTo(History h) {
// to be able to sort it in a TreeSet descending on frequency
// note that it is not resorted if you change frequencies, so
// build the set, and then convert it to a TreeSet afterwards.
return (frequency == h.frequency) ? 1 : (h.frequency - frequency);
}
}
Then create a HashMap to quickly fill history, and convert it into a TreeSet to sort: 然后创建一个HashMap以快速填充历史记录,并将其转换为TreeSet进行排序:
List<Move> moves = board.getMoves();
HashMap<History, History> fillTable = new HashMap<History, History>();
for (Move m : moves) {
History h = fillTable.get(m);
if (h == null) {
h = new History(m);
fillTable.put(h, h);
} else {
h.increment();
}
}
TreeSet<History> sorted = new TreeSet<History>(fillTable.values());
.... ready to use
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