Question

我正在努力做一个小组。我有以下列表：

 Date = 10/03 06:40 AM, Val = 10  
 Date = 10/03 08:55 PM, Val = 5  
 Date = 11/03 06:40 AM, Val = 5  
 Date = 11/03 10:50 AM, Val = 9  
 Date = 11/03 06:40 PM, Val = 14

我想要这个清单：

 Date = 10/03, Val = 5  
 Date = 11/03, Val = 14

因此，列表按Date.Date分组，但Val取决于Max(d => d.Date)。

我是用foreach做到的，但我很确定我们可以使用LINQ（groupby，select）做些更好的事情。有任何想法吗？

干杯

Answer 1

我相信你想要像

这样的东西

static T MaxBy<T, TKey>(this IEnumerable<T> source, Func<T, TKey> selector)
where TKey: IComparable<TKey> =>
    source.OrderByDescending(selector).First();

然后

from item in items
group item by item.Date.Date into byDate
select new
{
    Date = byDate.Key,
    byDate.MaxBy(item => item.Date).Val
}

如果您不想创建专用方法，您当然也可以内联

from item in items
group item by item.Date.Date into byDate
let ordered = from item in byDate
              orderby item.Date descending
              select item.Val
select new
{
    Date = byDate.Key,
    Val = ordered.First() 
}

注意：感谢mjwills指出了我能够纠正的错误

Answer 2

它应该是这样的：

export ANDROID_HOME={YOUR_PATH}

export PATH=$PATH:$ANDROID_HOME/tools:$ANDROID_HOME/platform-tools

source ~/.bash_profile

Answer 3

以下内容：

values
    .GroupBy(value => value.Date.Date)
    .Select(grouped => new
        {
            Date = grouped.Key,
            Val = values.First(value => value.Date == grouped.Date.Max()).Val
        });

Answer 4

以下是我最终的结果：

示例实体：

public class ExampleEntity
{
    public DateTime Date { get; set; }

    public int Val { get; set; }
}

示例代码：

var listOfExampleEntity = new List<ExampleEntity>()
        {
            new ExampleEntity()
            {
                Date = new DateTime(2018, 10, 03, 3, 40, 00),
                Val =2
            },
            new ExampleEntity()
            {
                Date = new DateTime(2018, 10, 03, 4, 40, 00),
                Val =2
            },new ExampleEntity()
            {
                Date = new DateTime(2018, 11, 03, 5, 40, 00),
                Val =5
            },new ExampleEntity()
            {
                Date = new DateTime(2018, 10, 03, 3, 40, 00),
                Val =2
            },new ExampleEntity()
            {
                Date = new DateTime(2018, 11, 03, 7, 40, 00),
                Val =3
            },new ExampleEntity()
            {
                Date = new DateTime(2018, 11, 03, 8, 40, 00),
                Val =4
            },
        };

        var temp = listOfExampleEntity.GroupBy(
                    p => p.Date.Date,
                    p => p.Val,
                    (date, val) => new { Date = date, Value = val.Last() });

按日期分组。日期

4 个答案: