從ArrayList中刪除重複項<HashMap <String，String >>

Question

我有一個arraylist，我想刪除最後添加的productId（14和1）的重複項。我試過這個，但是出現了錯誤。

Set<String> set = new LinkedHashSet<String>(); 
for (HashMap<String, String> list: modelData.displaylist) { 
    set.addAll ((Collection<? extends String>) list); 
} 
ArrayList<String> uniqueList = new ArrayList<String>(set); 
Log.e("uniqueList", "" + uniqueList); 

輸出我只想這個。

(2 = {HashMap@4692} size = 4 and 7 = {HashMap@4692} size = 4) 

我的ArrayList低於

displaylist = {ArrayList@4652} size = 10 
0 = {HashMap@4633} size = 4 
0 = {HashMap$HashMapEntry@5037} "spQuantity" -> "1" 
1 = {HashMap$HashMapEntry@5038} "prdName" -> "Aqua" 
2 = {HashMap$HashMapEntry@5039} "proprice" -> "20" 
3 = {HashMap$HashMapEntry@5040} "productId" -> "14" 

1 = {HashMap@4692} size = 4 
0 = {HashMap$HashMapEntry@5031} "spQuantity" -> "6" 
1 = {HashMap$HashMapEntry@5032} "prdName" -> "RailNeer" 
2 = {HashMap$HashMapEntry@5033} "proprice" -> "22" 
3 = {HashMap$HashMapEntry@5034} "productId" -> "1" 

2 = {HashMap@4715} size = 4 
0 = {HashMap$HashMapEntry@5022} "spQuantity" -> "1" 
2 = {HashMap$HashMapEntry@5024} "proprice" -> "20" 
1 = {HashMap$HashMapEntry@5023} "prdName" -> "RailNeer" 
3 = {HashMap$HashMapEntry@5025} "productId" -> "1" 


3 = {HashMap@4715} size = 4 
0 = {HashMap$HashMapEntry@5009} "spQuantity" -> "8" 
1 = {HashMap$HashMapEntry@5010} "prdName" -> "Aqua" 
2 = {HashMap$HashMapEntry@5011} "proprice" -> "20" 
3 = {HashMap$HashMapEntry@5012} "productId" -> "14" 


6 = {HashMap@4893} size = 4 
0 = {HashMap$HashMapEntry@4985} "spQuantity" -> "6" 
1 = {HashMap$HashMapEntry@4986} "prdName" -> "Aqua" 
2 = {HashMap$HashMapEntry@4987} "proprice" -> "20" 
3 = {HashMap$HashMapEntry@4988} "productId" -> "14" 

7 = {HashMap@4909} size = 4 
0 = {HashMap$HashMapEntry@4972} "spQuantity" -> "9" 
1 = {HashMap$HashMapEntry@4973} "prdName" -> "Aqua" 
2 = {HashMap$HashMapEntry@4974} "proprice" -> "20" 
3 = {HashMap$HashMapEntry@4975} "productId" -> "14" 

Answer 1

有幾件事情，我從你的問題發現，第一件事情是，你想投的散列映射爲一個集合（不能是）。如果你想擁有一套獨特的包含HashMap，那麼你可以簡單地做：

Set<HashMap<String, String>> set = new LinkedHashSet<String>(); 
set.addAll(modelData.displaylist) 
ArrayList<String> uniqueList = new ArrayList<String>(set); 

但是請注意，設定獨特將從HashMap的實例，而不是其內容。這導致我可以注意到的第二件事。在閱讀原始清單後，似乎您有一份產品清單，每個產品都重複使用，但產品的數量和價格不同（可能價格是錯誤的）。所以我認爲你想要做的是迭代原始列表，如果該列表不存在，則將產品添加到列表中;如果產品已經存在，則更新產品數量，可以使用列表完成該列表並迭代列表要知道如果產品已經存在

ArrayList<HashMap<String,String>> uniqueList = new ArrayList(); 
for (HashMap<String, String> prod: modelData.displaylist) { 
    HashMap<String, String> foundProd = null; 
    for (HashMap<String, String> uniqueProd: uniqueList) { 
     if (uniqueProd.get("productId").equals(prod.get("productId")) { 
      foundProd = uniqueProd; 
      break; 
     } 
    } 
    if (foundProd == null) { 
     uniqueList.add(prod); 
    } else { 
     // Do something if the product already existed (maybe update qty) 
    } 
} 
Log.e("uniqueList", "" + uniqueList); 

更新

要想從列表中的最後一個元素，你可以使用相同的代碼，但（倒數第一項），通過以相反的順序列表中行走：

for (int i = modelData.displayList.size() - 1; i >= 0; i--) { 
    final HashMap<String, String> prod = (HashMap<String, String) modelData.displayList.get(i); 
    ... 
} 

或者你可以使用一個HashMap，而不是有條件接入列表上的元素，然後創建一個HashMap的值的列表：

HashMap<String, HashMap<String,String>> tempMap = new HashMap<String, String>(); 
for (HashMap<String, String> prod: modelData.displaylist) { 
    // Always override 
    tempMap.put(prod.get("productId"), prod); 
} 
ArrayList<HashMap<String,String>> uniqueList = new ArrayList(tempMap.values()); 
Log.e("uniqueList", "" + uniqueList);