需要有关 C# LINQ 列表聚合表达式的建议

Question

假设我有价格类型列表：

[
    {
        "Id": 57571,
        "Price": 1745.0,
        "DateAdded": "2018-12-01T00:00:00"
    },
    {
        "Id": 67537,
        "Price": 1695.0,
        "DateAdded": "2018-09-24T00:00:00"
    },
    {
        "Id": 80042,
        "Price": 1645.0,
        "DateAdded": "2019-03-24T00:00:00"
    },
    {
        "Id": 155866,
        "Price": 1545.0,
        "DateAdded": "2019-04-24T00:00:00"
    },
    {
        "Id": 163643,
        "Price": 1545.0,
        "DateAdded": "2019-04-26T00:00:00"
    },
    {
        "Id": 171379,
        "Price": 1545.0,
        "DateAdded": "2019-04-27T00:00:00"
    },
    {
        "Id": 178990,
        "Price": 1545.0,
        "DateAdded": "2019-04-28T00:00:00"
    }
]

我需要删除所有具有相同价格的项目，但前提是该项目是列表元素的兄弟项。有没有用LINQ实现的？

我的预期输出是

[
    {
        "Id": 57571,
        "Price": 1745.0,
        "DateAdded": "2018-12-01T00:00:00"
    },
    {
        "Id": 67537,
        "Price": 1695.0,
        "DateAdded": "2018-09-24T00:00:00"
    },
    {
        "Id": 80042,
        "Price": 1645.0,
        "DateAdded": "2019-03-24T00:00:00"
    },
    {
        "Id": 155866,
        "Price": 1545.0,
        "DateAdded": "2019-04-24T00:00:00"
    }
]

我完全不知道如何才能做到这一点。我很感激任何建议。

Answer 1

您可以简单地使用迭代器这样做：

using System;
using System.Collections.Generic;

public class Test
{
    public static void Main()
    {
        var input = new[] { 1, 2, 2, 3, 4, 4, 3, 2, 2, 1 };

        var output = GetUniqueAdjacent(input);

        foreach (var o in output)
        {
            Console.WriteLine(o);
        }
    }

    public static IEnumerable<int> GetUniqueAdjacent(IEnumerable<int> input)
    {
        bool first = true;
        int previous = -1;
        foreach (var i in input)
        {
            if (first)
            {
                previous = i;
                yield return i;
                first = false;
                continue;
            }

            if (i == previous)
            {
                previous = i;
                continue;
            }

            previous = i;
            yield return i;
        }
    }
}

这会输出 1, 2, 3, 4, 3, 2, 1，仅删除相邻的重复项。

Answer 2

通过使用 Microsoft 的 C# 文档中的 ChunkBy extension 方法，您可以

myData.ChunkBy(x => x.Price).Select(g => g.First())

...或者使用 MoreLinq's GroupAdjacent 你可以

myData.GroupAdjacent(x => x.Price).Select(g => g.First())

Answer 3

这可以通过常规 Where 调用来完成。

int? previousPrice = null;

var output = myData.Where(d => {
  var result = !previousPrice.HasValue || previousPrice.Value != d.Price;
  previousPrice = d.Price;
  return result;
}).ToList();

需要有关 C# LINQ 列表聚合表达式的建议

Need advice for C# LINQ List aggregation expression

c#

linq

list

aggregation