Linq 查询分组依据和选择第一项 [英] Linq Query Group By and Selecting First Items

问题描述

我有一个像这样的字符串数组:

I have a String array kinda like this:

// icon, category, tool
String[,] subButtonData = new String[,]
{
    {"graphics/gui/brushsizeplus_icon", "Draw", "DrawBrushPlus"},
    {"graphics/gui/brushsizeminus_icon", "Draw", "DrawBrushMinus"},
    {"graphics/gui/freedraw_icon", "Draw", "DrawFree"},
    {"graphics/gui/linedraw_icon", "Draw", "DrawLine"},
    {"graphics/gui/rectangledraw_icon", "Draw", "DrawRectangle"},
    {"graphics/gui/ellipsedraw_icon", "Draw", "DrawEllipse"},
    {"graphics/gui/brushsizeplus_icon", "Brusher", "BrusherBrushPlus"},
    {"graphics/gui/brushsizeminus_icon", "Brusher", "BrusherBrushMinus"},
    {"graphics/gui/brushsizeplus_icon", "Text", "TextBrushPlus"},
    {"graphics/gui/brushsizeminus_icon", "Text", "TextBrushMinus"},
};

然后我用名为 mainButtons

这是我查询Category 分组的方式:

This is how I query for grouping for Category:

var categories = from b in mainButtons
                 group b by b.category into g
                 select new { Category = g.Key, Buttons = g };

如何选择主列表中每个组的第一项?(不迭代每个并添加到另一个列表?)

How can I select the first item of each group in my main List? (without iterating each and adding to another List?)

推荐答案

参见 LINQ:如何使用 group by 子句获取最新/最后一条记录

var firstItemsInGroup = from b in mainButtons
                 group b by b.category into g
select g.First();

我假设 mainButtons 已经正确排序.

I assume that mainButtons are already sorted correctly.

如果您需要指定自定义排序顺序，请使用带有比较器的 OrderBy 覆盖.

If you need to specify custom sort order, use OrderBy override with Comparer.

var firstsByCompareInGroups = from p in rows
        group p by p.ID into grp
        select grp.OrderBy(a => a, new CompareRows()).First();

在我的帖子中看到一个例子 使用自定义比较器选择组中的第一行"

See an example in my post "Select First Row In Group using Custom Comparer"

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