使用LINQ将增量属性按组添加到IEnumerable [英] Add incremented property to IEnumerable by group using LINQ

问题描述

为简化方案，假设我们有一个具有FirstName和LastName属性的人员列表.

To simplify the scenario, let's say we have a list of People with FirstName and LastName properties.

我们的数据如下:

Bob    Smith
Jane   Smith
Todd   Grover
Larry  Lewis
Jill   Lewis
Frank  Lewis

第一步是添加一个Integer属性，该属性将为每个项目递增:

The first step would be to add an Integer property that gets incremented for each item:

Bob    Smith  1
Jane   Smith  2
Todd   Grover 3
Larry  Lewis  4
Jill   Lewis  5
Frank  Lewis  6

理想情况下，我想为每个新组重置计数器以实现此目的:

Ideally, I'd like to reset the counter for every new group to achieve this:

Bob    Smith  1
Jane   Smith  2
Todd   Grover 1
Larry  Lewis  1
Jill   Lewis  2
Frank  Lewis  3

也许LINQ不适合.看起来LINQ应该可以优雅地做到这一点.

Maybe LINQ isn't appropriate. It just seems like LINQ should be able to do this elegantly.

推荐答案

如果您只希望计数器随每个项目递增:

If you just want a counter that increments with each item:

var query = people
    .Select((x, i) => new { x.FirstName, x.LastName, Index = i + 1 });

或者如果要重置每个组的计数器，则按LastName分组:

Or if you want to reset the counter for each group, grouped by LastName:

var query = people
    .GroupBy(x => x.LastName)
    .Select
    (
        x => x.Select((y, i) => new { y.FirstName, y.LastName, Index = i + 1 })
    )
    .SelectMany(x => x);

并快速显示查询结果:

foreach (var item in query)
{
    Console.WriteLine(item.FirstName + "\t" + item.LastName + "\t" + item.Index);
}

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