Linq Orderby和与众不同 [英] Linq orderby and distinct

问题描述

我的表格设置如下:

Section SectionOrder
Sect1     1 
Sect2     2 
Sect3     3 
Sect3     3 
Sect1     1
Sect2     2

我需要按正确的部分顺序拉出不同的部分.这是我正在使用的linq，但是由于某种原因，它并没有按正确的顺序排列它们.

I need to pull out distinct sections in correct section order. Here is the linq that I'm using, but it's not putting them in the correct order for some reason.

var myVar = (from x in context.Documents 
             orderby x.SectionOrder ascending
             select x.Section).Distinct(); 

然后，我希望能够遍历myVar并将每个项目放在列表中，如下所示:

I then want to be able to loop through myVar and put each item in a list as follows:

foreach (var t in myVar)
        {
             listOfDocTypeSections.Add(t);
        }

推荐答案

OrderBy和Distinct的顺序很重要:虽然OrderBy产生了有序序列，但Distinct却没有.您需要先放置Distinct，然后再使用OrderBy.但是，由于您在一个属性上使用Distinct，在另一个属性上进行排序，因此您需要以不同的方式进行操作:

The ordering of OrderBy and Distinct matters: while OrderBy produced an ordered sequence, Distinct doesn't. You need to put Distinct first, and then use OrderBy. However, since you take Distinct on one attribute, and order on the other attribute, you need to do it differently:

var myVar = context
    .Documents
    .GroupBy(x => x => x.Section) // This replaces Distinct()
    .OrderBy(g => g.FirstOrDefault().SectionOrder) // There will be no default
    .Select(g => g.Key);

此方法将Distinct替换为GroupBy，并在组的第一个SectionOrder项目上下订单.您可以更改此排序策略以对Section中的其他某些项进行排序，例如SectionOrder的Min或Max值:

This approach replaces Distinct with GroupBy, and orders on the first SectionOrder item of a group. You can change this sorting strategy to sort on some other item within the Section, say, Min or Max value of SectionOrder:

var myVar = context
    .Documents
    .GroupBy(x => x => x.Section)
    .OrderBy(g => g.Max(x => x.SectionOrder))
    .Select(g => g.Key);

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