根据关键字段列表删除数据表的重复行

Question

我正在使用以下代码根据一个字段 (keyField)

的值删除 DataTable 中的重复行

IEnumerable<DataRow> uniqueContacts = dt.AsEnumerable()
                    .GroupBy(x =>  x[keyField].ToString())
                    .Select(g => g.First());
DataTable dtOut = uniqueContacts.CopyToDataTable();

如何升级此代码，以便我的 LINQ 根据字段列表的值删除重复项。例如删除具有相同 'firstname' 和 'lastname'?

的所有行

Answer 1

您可以使用匿名类型：

IEnumerable<DataRow> uniqueContacts = dt.AsEnumerable()
                    .GroupBy(row =>  new { 
                        FirstName = row.Field<string>("FirstName"),
                        LastName  = row.Field<string>("LastName")
                    })
                    .Select(g => g.First());

因为你想要一个在编译时未知的 List<string> 的解决方案，你可以使用这个 class:

public class MultiFieldComparer : IEquatable<IEnumerable<object>>, IEqualityComparer<IEnumerable<object>>
{
    private IEnumerable<object> objects;

    public MultiFieldComparer(IEnumerable<object> objects)
    {
        this.objects = objects;
    }

    public bool Equals(IEnumerable<object> x, IEnumerable<object> y)
    {
        return x.SequenceEqual(y);
    }

    public int GetHashCode(IEnumerable<object> objects)
    {
        unchecked
        {
            int hash = 17;
            foreach (object obj in objects)
                hash = hash * 23 + (obj == null ? 0 : obj.GetHashCode());
            return hash;
        }
    }

    public override int GetHashCode()
    {
        return GetHashCode(this.objects);
    }

    public override bool Equals(object obj)
    {
        MultiFieldComparer other = obj as MultiFieldComparer;
        if (other == null) return false;
        return this.Equals(this.objects, other.objects);
    }

    public bool Equals(IEnumerable<object> other)
    {
        return this.Equals(this.objects, other);
    }
}

以及使用此 class 的扩展方法：

public static IEnumerable<DataRow> RemoveDuplicates(this IEnumerable<DataRow> rows, IEnumerable<string> fields)
{
    return rows
        .GroupBy(row => new MultiFieldComparer(fields.Select(f => row[f])))
        .Select(g => g.First());
}

那么就很简单了：

List<string> columns = new List<string> { "FirstName", "LastName" };
var uniqueContacts = dt.AsEnumerable().RemoveDuplicates(columns).CopyToDataTable();

根据关键字段列表删除数据表的重复行

Remove duplicate rows of a datatable based on a list of key fields

c#

linq

datatable