我的列表包含看起來像這樣的數據game_id | user_id | status 1 1 STARTED 2 1 FINISHED 1 2 STARTED 2 2 FINISHED我想將此列表收集到兩個地圖中（或者如果可能的話在單個地圖中）一張地圖應保持與user_id用戶玩過的游戲數量的映射 - 基本上是帶有finished狀態的游戲user_id | finished_games 1 1 2 1另一張地圖應存儲user_id到所有游戲計數。它看起來像這樣user_id | all_games 1 2 2 2我這樣做（我刪除了game_id字段，因為它實際上并不重要）import java.util.*;import java.util.stream.*;public class MyClass { public static void main(String args[]) { List<Game> games = Arrays.asList( create("user-1", "STARTED"), create("user-2", "STARTED"), create("user-1", "FINISHED"), create("user-2", "FINISHED"), create("user-1", "FINISHED"), create("user-2", "FINISHED") ); // expect user-1: all_games (3), finished_games (2) Map<String, Long> allGames = games .stream() .collect(Collectors.groupingBy(Game::getUserId, Collectors.counting())); System.out.println(allGames); Map<String, Long> finishedGames = games .stream() .filter(game -> game.battleStatus.equals("FINISHED")) .collect(Collectors.groupingBy(Game::getUserId, Collectors.counting())); System.out.println(finishedGames); } private static Game create(String id, String status) { Game game = new Game(); game.userId = id; game.battleStatus = status; return game; } private static class Game { String userId; String battleStatus; public String getUserId() { return userId; } }}它似乎工作正常。但是當我計算帶有狀態的游戲時，我會進行過濾以便只留下帶有FINISHED狀態的項目。Map<String, Long> finishedGames = games .stream() .filter(game -> game.battleStatus.equals("FINISHED")) .collect(Collectors.groupingBy(Game::getUserId, Collectors.counting()));有沒有辦法實現內部collect塊而不是使用filter？
2 回答
揚帆大魚
TA貢獻1799條經驗 獲得超9個贊
您可以使用多個groupingBy來獲得這個，例如：
Map<String, Map<String, Long>> gameStatuses = games
.stream()
.collect(Collectors.groupingBy(Game::getUserId,
Collectors.groupingBy(Game::getBattleStatus, Collectors.counting())));
System.out.println(gameStatuses);
為此，您需要為Game類添加一個吸氣劑battleStatus，例如：
private static class Game {
String userId;
String battleStatus;
public String getUserId() {
return userId;
}
public String getBattleStatus() {
return battleStatus;
}
}
這將為您提供以下輸出：
{user-1={STARTED=1, FINISHED=2}, user-2={STARTED=1, FINISHED=2}}
您可以使用嵌套map.get來獲取任何用戶和任何狀態的計數。
ibeautiful
TA貢獻1993條經驗 獲得超6個贊
如果您需要計算已完成和未完成的游戲，那么另一個groupingBy可以幫助您：
Function<Game, Boolean> isFinished = game -> "FINISHED".equals(game.battleStatus);
Map<String, Map<Boolean, Long>> groupedGames =
games.stream()
.collect(groupingBy(Game::getUserId,
groupingBy(isFinished, counting())));
或者您可能想自己分組battleStatus：
Map<String, Map<String, Long>> groupedGames =
games.stream()
.collect(groupingBy(Game::getUserId,
groupingBy(game -> game.battleStatus, counting())));
我什至會創建一個吸氣劑getBattleStatus()，然后game -> game.battleStatus用方法參考替換Game::getBattleStatus：
Map<String, Map<String, Long>> groupedGames =
games.stream()
.collect(groupingBy(Game::getUserId,
groupingBy(Game::getBattleStatus, counting())));
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