在 LINQ GroupBy 函数中使用匿名类型的 IEqualityComparer

Question

作为 LINQ 连接操作的结果，我有一个 匿名类型 的 IEnumerable。列表的一些值是：

    { CellId = 0, CellIndex = "1", CellDataType = "String", CellValue = "Id", RowNumber = 0 }
    { CellId = 1, CellIndex = "2", CellDataType = "String", CellValue = "first_name", RowNumber = 0 }
    { CellId = 2, CellIndex = "3", CellDataType = "String", CellValue = "age", RowNumber = 0 }
    { CellId = 3, CellIndex = "4", CellDataType = "String", CellValue = "child_name", RowNumber = 0 }
    { CellId = 4, CellIndex = "5", CellDataType = "String", CellValue = "child_age", RowNumber = 0 }
    { CellId = 5, CellIndex = "1", CellDataType = "Number", CellValue = "1", RowNumber = 1 }
    { CellId = 6, CellIndex = "2", CellDataType = "String", CellValue = "john", RowNumber = 1 }
     .
     .
     .

（数据来自excel sheet）你可以看到rowNumber = 0的objects有table的列名。

从传播sheet你可以注意到 John (id=1) 有 3 children，所以我想按 id 分组并有类似的东西：

Id = 1
    first_name = "john", age = 30, child_name = "Andy", child_age = 4
    first_name = "john", age = 30, child_name = "Anna", child_age = 6
    first_name = "john", age = 30, child_name = "Lily", child_age = 8

Id = 2
    first_name = "Emily", age = 32, child_name = "Harry", child_age = 3
    first_name = "Emily", age = 32, child_name = "David", child_age = 3

Id = 3
    first_name = "Peter", age = 40, child_name = "Carol", child_age = 2

我假设 Linq GroupBy 可以做到这一点。问题是：

列表的元素是 anonymous type 并且它的属性是通用的 objects。 CellId、CellIndex、RowNumber 将始终是整数，因此我可以使用强制转换，但未定义 CellValue，它可以是字符串、整数等。

我可以制作一个IEnumerable of Anonymous Type <int, int, string, string, int>。我基本上是将 CellId 转换为 int，将 CellIndex 转换为 int，将 CellValue 转换为字符串，将 CellDataType 转换为字符串，将 RowNumber 转换为 int。但我仍然不确定如何进行分组。

如何将它们分组？

为了比较 Id 是否相等，我需要查找 CellIndex = 1（对应于列名 Id），然后使用 CellValue 属性（相同的匿名类型元素）看是否相等。

基本上我需要按 CellValue 分组，但仅适用于 CellIndex = 1 的那些。

有什么建议吗？

Answer 1

也许这会对您有所帮助：

var list = new [] {
    new { CellId = 0, CellIndex = "1", CellDataType = "String", CellValue = "Id", RowNumber = 0 },
    new { CellId = 1, CellIndex = "2", CellDataType = "String", CellValue = "first_name", RowNumber = 0 },
    new { CellId = 2, CellIndex = "3", CellDataType = "String", CellValue = "age", RowNumber = 0 },
    new { CellId = 3, CellIndex = "4", CellDataType = "String", CellValue = "child_name", RowNumber = 0 },
    new { CellId = 4, CellIndex = "5", CellDataType = "String", CellValue = "child_age", RowNumber = 0 },
    new { CellId = 5, CellIndex = "1", CellDataType = "Number", CellValue = "1", RowNumber = 1 },
    new { CellId = 6, CellIndex = "2", CellDataType = "String", CellValue = "john", RowNumber = 1 },
    new { CellId = 5, CellIndex = "1", CellDataType = "Number", CellValue = "1", RowNumber = 2 },
    new { CellId = 6, CellIndex = "2", CellDataType = "String", CellValue = "john", RowNumber = 2 },
    new { CellId = 5, CellIndex = "1", CellDataType = "Number", CellValue = "2", RowNumber = 3 },
    new { CellId = 6, CellIndex = "2", CellDataType = "String", CellValue = "emily", RowNumber = 3 },
};

var result = list
    .GroupBy(x => x.RowNumber)
    //.Where(x => x.Key > 0)//in case you want to skip you header row
    .Select(x => new {  
        Id = x.SingleOrDefault(t => t.CellIndex == "1").CellValue,
        first_name = x.SingleOrDefault(t => t.CellIndex == "2")?.CellValue,
        age = x.SingleOrDefault(t => t.CellIndex == "3")?.CellValue,
        child_name = x.SingleOrDefault(t => t.CellIndex == "4")?.CellValue,
        child_age = x.SingleOrDefault(t => t.CellIndex == "5")?.CellValue
    })
    .GroupBy(x => x.Id);

主要思想是先按 RowNumber 分组，然后将数据转换为 Id 最后按 Id.

分组

Answer 2

您有一组单元格，但您想要的是一组记录。在获取 groups 条记录之前，您需要先获取 records。如何从单元格中获取记录？

记录和行之间存在 one-to-one 关系，因此您可以从将单元格分组到行开始：

var rows = joinQuery
    .GroupBy(j => j.RowNumber)
    .Where(g => g.Key != 0); // Ignore the header row

现在每个组代表一行，该组的元素是单元格。要将这些组转换为记录，您需要将单元格转换为记录字段。如何将单元格转换为记录字段？

CellIndex 和字段类型之间存在映射：“1”是Id，“2”是first_name，依此类推。因此，从单元格创建字典查找：

var lookup = rows
    .Select(g => g.ToDictionary(cell => cell.CellIndex, cell => cell.CellValue));

现在您已经有了一系列以 CellIndex 为关键字的字典，利用从 CellIndex 到字段的映射。使用 GetValueOrDefault:

处理字段不存在的情况

var records = lookup.Select(l => new
{
    Id = l.GetValueOrDefault("1"),
    first_name = l.GetValueOrDefault("2"),
    age = l.GetValueOrDefault("3"),
    child_name = l.GetValueOrDefault("4"),
    child_age = l.GetValueOrDefault("5")
});

现在你有记录了。最后一步是按 Id:

对它们进行分组

var groups = records.GroupBy(r => r.Id).ToArray();

foreach (var group in groups)
{
    Console.WriteLine($"Id = {group.Key}");
    foreach (var record in group)
    {
        Console.WriteLine($"    first_name = {record.first_name}, age = {record.age}, child_name = {record.child_name}, child_age = {record.child_age}");
    }
    Console.WriteLine();
}

// Outputs:
Id = 1
    first_name = john, age = 30, child_name = Andy, child_age = 4
    first_name = john, age = 30, child_name = Anna, child_age = 6
    first_name = john, age = 30, child_name = Lily, child_age = 8

Id = 2
    first_name = Emily, age = 32, child_name = Harry, child_age = 3
    first_name = Emily, age = 32, child_name = David, child_age = 3

Id = 3
    first_name = Peter, age = 40, child_name = Carol, child_age = 2

在 LINQ GroupBy 函数中使用匿名类型的 IEqualityComparer

Using a IEqualityComparer for Anoymous Type in a LINQ GroupBy function

c#

.net

linq

anonymous-types

iequalitycomparer