[英]How can I get distinct values of a specific column in arrayList
假设我有这个 arrayList :
ArrayList<Personne> personnes = new ArrayList<Personne>();
Personne p1 = new Personne("001590842","51862499", "N5+", "1", "20170201","0");
Personne p2 = new Personne("001590842","51862499", "X0", "1", "20150529", "1");
Personne p3 = new Personne("001639055","51862517", "G3", "1", "20170201", "2");
Personne p4 = new Personne("001639055","51862517", "G3", "1", "20170201", "2");
Personne p5 = new Personne("001597135","51862517", "G3", "1", "20170201", "2");
Personne p6 = new Personne("001597135","51862517", "G3", "1", "20170201", "2");
Personne p7 = new Personne("002804935","00006178","G4","1","19870101","1");
Personne p8 = new Personne("002804935","00009118","X0","1","19861201","1");
Personne p9 = new Personne("002804935","00009957","N4+","1","19861229","1");
Personne p10 = new Personne("002804935","00012970","B3++","1","20100227","1");
personnes.add(p1);
personnes.add(p2);
personnes.add(p3);
personnes.add(p4);
personnes.add(p5);
personnes.add(p6);
personnes.add(p7);
personnes.add(p8);
personnes.add(p9);
personnes.add(p10);
然后我只想获得第一列的不同值。 所以需要的结果应该是:
001590842
001639055
002804935
请注意,我的 Personne 类定义为:
public class Personne {
private String IDT_GCT;
private String IDC_PSE_PCL;
private String IDC_CD_NOT;
private String DA_PRM_CTR_ORDER;
private String IDT_ETT_PSE;
private String CD_NOT;
public Personne(String IDT_GCT, String IDC_PSE_PCL, String IDC_CD_NOT,
String DA_PRM_CTR_ORDER, String IDT_ETT_PSE, String CD_NOT) {
this.IDT_GCT = IDT_GCT;
this.IDC_PSE_PCL = IDC_PSE_PCL;
this.IDC_CD_NOT = IDC_CD_NOT;
this.DA_PRM_CTR_ORDER = DA_PRM_CTR_ORDER;
this.IDT_ETT_PSE = IDT_ETT_PSE;
this.CD_NOT = CD_NOT;
}
public String getIDC_CD_NOT() {
return this.IDC_CD_NOT;
}
public String getIDC_PSE_PCL() {
return this.IDC_PSE_PCL;
}
public String getDA_PRM_CTR_ORDER() {
return this.DA_PRM_CTR_ORDER;
}
public String getIDT_ETT_PSE() {
return this.IDT_ETT_PSE;
}
public String getCD_NOT() {
return this.CD_NOT;
}
public String getIDT_GCT() {
return this.IDT_GCT;
}
}
所以我需要获得 IDT_GCT 变量的不同值。
所以我创建了这个函数来返回这个:
private static List DistinctValues (ArrayList<Personne> listPersonnes)
{
List <String> outList = listPersonnes.stream().map(m -> m.get("IDT_GCT")).distinct().collect(Collectors.toList());
return(outList);
}
但这会返回一个错误:
Multiple markers at this line
- Cannot infer type argument(s) for <R> map(Function<? super T,? extends R>)
- The method get(String) is undefined for the type Personne
- The type List is not generic; it cannot be parameterized with arguments <String>
请问我该如何解决?
方法 get(String) 未定义为 Personne 类型
你应该使用getIDT_GCT()
代替
private List DistinctValues(ArrayList listPersonnes) { Set uniqueColumnValues = new HashSet <>(); // 哈希集包含唯一值 listPersonnes.forEach(item -> uniqueColumnValues.add(item.getIDT_GCT())); // 向 HashSet 添加值 return uniqueColumnValues.stream().collect(Collectors.toList()); }
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