LINQ简明教程：数据排序、分组、过滤

LINQ可以对很多数据源进行查询操作，比如数据库、数组（array）、链表（list）、XML文件等。在本文中，我将从数组中提取数据，这些数据是10个最受欢迎的国家。有一个类叫Countries，有country, population and continent这些属性。我们将以Countries类为元素的数组作为数据源，绑定到GridView进行显示，并且利用LINQ对数据进行排序、分组和过滤。

下面是一些效果图：

代码

下面就是Countries类：

public class Countries
{
    public string Country
    {
        get;
        set;
    }
    public long Population
    {
        get;
        set;
    }
    public string Continent
    {
        get;
        set;
    }
}

下面的Page_Load函数将对 Countries类数组进行初始化：

protected void Page_Load(object sender, EventArgs e)
{
    for (int ctr = 0; ctr < cc.Length;ctr++ )
    {
        cc[ctr] = new Countries();
    }
    cc[0].Country = "Bangladesh";
    cc[0].Population = 156594962;
    cc[0].Continent = "Asia";
    cc[1].Country = "Brazil";
    cc[1].Population = 200361925;
    cc[1].Continent = "America";
    cc[2].Country = "China";
    cc[2].Population = 1357380000;
    cc[2].Continent = "Asia";
    cc[3].Country = "India";
    cc[3].Population = 1252139596;
    cc[3].Continent = "Asia";
    cc[4].Country = "Indonesia";
    cc[4].Population = 249865631;
    cc[4].Continent = "Asia";
    cc[5].Country = "Japan";
    cc[5].Population = 127338621;
    cc[5].Continent = "Asia";
    cc[6].Country = "Nigeria";
    cc[6].Population = 173615345;
    cc[6].Continent = "Africa";
    cc[7].Country = "Pakistan";
    cc[7].Population = 182142594;
    cc[7].Continent = "Asia";
    cc[8].Country = "Russian Federation";
    cc[8].Population = 143499861;
    cc[8].Continent = "Europe";
    cc[9].Country = "United States";
    cc[9].Population = 316128839;
    cc[9].Continent = "America";
    btnDisplay_Click(sender, e);
}

点击展示按钮后，即可将数据绑定到GridView：

protected void btnDisplay_Click(object sender, EventArgs e)
{
    Label2.Text = "Alphabetical List";
    var info = from i in cc select i;
    GridView1.DataSource = info;
    GridView1.DataBind();
}

下面的代码是利用LINQ对数据进行排序：

protected void btnAsc_Click(object sender, EventArgs e)
{
    Label2.Text = "In Ascending Order of Population";
    var info = from i in cc orderby i.Population select i;
    GridView1.DataSource = info;
    GridView1.DataBind();
}
protected void btnDesc_Click(object sender, EventArgs e)
{
    Label2.Text = "In Descending Order of Population";
    var info = from i in cc orderby i.Population descending select i;
    GridView1.DataSource = info;
    GridView1.DataBind();
}

正如你上面所看到的，orderby 可以指定按population属性正向排序还是反向排序。

下面的代码我们将利用LINQ实现按country分组的功能，并且列出国家的数量、总人口数以及平均人口数：

protected void btnGroup_Click(object sender, EventArgs e)
{
    Label2.Text = "Continent Wise Group Data";
    var info = from i in cc
               orderby i.Continent
               group i by i.Continent into g
               select new
               {
                   Continent = g.Key,
                   NumberOfCountries = g.Count(),
                   TotalPopulation = g.Sum(s => s.Population),
                   AveragePopulation = g.Average(a => a.Population)
               };
    GridView1.DataSource = info;
    GridView1.DataBind();
}

groupby 操作可以实现不同的分组效果，我们可以根据 Count(), Sum(), Average()等方式来分组。

下面的代码将利用LINQ对数据进行过滤：

protected void btnShow_Click(object sender, EventArgs e)
{
    Label2.Text = "Data Filtered by Country Name";
    var info = from i in cc where i.Country.ToUpper() == txtCountry.Text.Trim().ToUpper() select i;
    GridView1.DataSource = info;
    GridView1.DataBind();
}

where 操作可以指定数据过滤的条件，比如你可以根据国家名称来过滤。