c# - 如何使用linq删除项目

Question

我有以下数组，它代表我试图从某个数据结构实例中删除的项目:

string[] diseasesToRemove = new string[] { "D1", "D3", "D5" };

我可以使用以下方法做到这一点:

for (int i = 0; i < healthGroup.DiseaseGroups.Length; i++)
{
    var dgDiseases = new List<Disease>(healthGroup.DiseaseGroups[i].Diseases);
    for (int j = 0; j < dgDiseases.Count; j++)
    {
        if (diseasesToRemove.Contains(dgDiseases[j].Name))
        {                 
            dgDiseases.RemoveAt(j);
            j--;
        }
    }
    healthGroup.DiseaseGroups[i].Diseases = dgDiseases.ToArray();
}

不过，我确信有更好的方法使用 Linq 或其他工具。有吗？

这里是类:

public class HealthGroup
{
    public DiseaseGroup[] DiseaseGroups { get; set; }

    public HealthGroup(DiseaseGroup[] diseaseGroups)
    {
        DiseaseGroups = diseaseGroups;
    }
}

public class DiseaseGroup
{
    public string Name { get; set; }
    public Disease[] Diseases;

    public DiseaseGroup(string name, Disease[] diseases)
    {
        Name = name;
        Diseases = diseases;
    }
}

public class Disease
{
    public string Name { get; set; } = "My Disease";
    public int Risk { get; set; } = 7;

    public Disease(string name, int risk)
    {
        Name = name;
        Risk = risk;
    }

    public override string ToString()
    {
        return $"{Name} with risk {Risk}";
    }
}

还有一些生成实例的样板:

Disease d1 = new Disease("D1", 1);
Disease d2 = new Disease("D2", 2);
Disease d3 = new Disease("D3", 3);
Disease d4 = new Disease("D4", 4);
Disease d5 = new Disease("D5", 5);
Disease d6 = new Disease("D6", 6);
Disease d7 = new Disease("D7", 7);

DiseaseGroup dg1 = new DiseaseGroup("DG1", new Disease[] { d1, d2 });
DiseaseGroup dg2 = new DiseaseGroup("DG2", new Disease[] { d3, d4, d5 });
DiseaseGroup dg3 = new DiseaseGroup("DG3", new Disease[] { d6, d7 });

HealthGroup healthGroup = new HealthGroup(new DiseaseGroup[] { dg1, dg2, dg3 });

Answer 1

你可以使用 Where将代码简化为:

foreach (var diseaseGroup in healthGroup.DiseaseGroups)
{
    diseaseGroup.Diseases 
        = diseaseGroup.Diseases.Where(g => !diseasesToRemove.Contains(g.Name)).ToArray();
}

当然，与原始代码一样，这会生成一个新列表。一个性能更高的选项(尽管是非 LINQ)可能是制作 Diseases一个List<Disease> :

public class DiseaseGroup
{
    public string Name { get; set; }
    public List<Disease> Diseases;

    public DiseaseGroup(string name, Disease[] diseases)
    {
        Name = name;
        Diseases = new List<Disease>(diseases);
    }
}

然后您可以使用类似的代码，而无需生成新列表和新数组的开销:

for (int i = 0; i < healthGroup.DiseaseGroups.Length; i++)
{
    for (int j = healthGroup.DiseaseGroups[i].Diseases.Count - 1; j >= 0; --j)
    {
        if (diseasesToRemove.Contains(healthGroup.DiseaseGroups[i].Diseases[j].Name))
        {                 
            healthGroup.DiseaseGroups[i].Diseases.RemoveAt(j);
        }
    }
}

我还修改了您的 for 循环以向后工作以解决您在 --j 中遇到的问题部分。

并且，而不是使用 string[]对于 diseasesToRemove ，对于大量项目，使用 HashSet<string> 可能会更好储存疾病。

---

编辑以包括请求的一行:

healthGroup.DiseaseGroups = healthGroup.DiseaseGroups.Select(g => { return g.Diseases = g.Diseases.Where(g => !diseasesToRemove.Contains(g.Name)).ToArray(); }).ToArray();

不过，这有点滥用选择 :-)