c# - Linq 分组除列

Question

我有一个包含大量属性的类，我需要按几乎所有列对其进行分组。

class Sample {
    public string S1 { get; set; }
    public string S2 { get; set; }
    public string S3 { get; set; }
    public string S4 { get; set; }
    // ... all the way to this:
    public string S99 { get; set; }

    public decimal? N1 { get; set; }
    public decimal? N2 { get; set; }
    public decimal? N3 { get; set; }
    public decimal? N4 { get; set; }
    // ... all the way to this:
    public decimal? N99 { get; set; }
}

有时我需要按除一两个十进制列之外的所有列进行分组，并基于此返回一些结果(即具有所有字段的对象，但带有一些十进制值作为总和或最大值)。

是否有任何扩展方法可以让我做这样的事情:

sampleCollection.GroupByExcept(x => x.N2, x => x.N5).Select(....);

而不是指定对象中的所有列？

Answer 1

借用这个答案 here:

创建类(class) EqualityComparer

public class EqualityComparer<T> : IEqualityComparer<T>
{
    public bool Equals(T x, T y)
    {
        IDictionary<string, object> xP = x as IDictionary<string, object>;
        IDictionary<string, object> yP = y as IDictionary<string, object>;

        if (xP.Count != yP.Count)
            return false;
        if (xP.Keys.Except(yP.Keys).Any())
            return false;
        if (yP.Keys.Except(xP.Keys).Any())
            return false;
        foreach (var pair in xP)
            if (pair.Value.Equals( yP[pair.Key])==false)
                return false;
        return true;

    }

    public int GetHashCode(T obj)
    {
        return obj.ToString().GetHashCode();
    }
}

然后创建您的 GroupContent方法:

private void GroupContent<T>(List<T> dataList, string[] columns, string[] columnsToExclude)
    {
string[] columnsToGroup = columns.Except(columnsToExclude).ToArray();
        EqualityComparer<IDictionary<string, object>> equalityComparer = new EqualityComparer<IDictionary<string, object>>();
        var groupedList = dataList.GroupBy(x =>
        {
            var groupByColumns = new System.Dynamic.ExpandoObject();
            ((IDictionary<string, object>)groupByColumns).Clear();
            foreach (string column in columnsToGroup)
                ((IDictionary<string, object>)groupByColumns).Add(column, GetPropertyValue(x, column));
            return groupByColumns;
        }, equalityComparer);


        foreach (var item in groupedList)
        {
            Console.WriteLine("Group : " + string.Join(",", item.Key));
            foreach (object obj in item)
                Console.WriteLine("Item : " + obj);
            Console.WriteLine();
        }

    }

    private static object GetPropertyValue(object obj, string propertyName)
    {
        return obj.GetType().GetProperty(propertyName).GetValue(obj, null);
    }