[C# Lambda] DataTable.AsEnumerable()使用範例

範例

0. 篩選

class Program
{
    static void Main()
    {
        DataTable table = GetSampleDataTable();

        var filteredRows = table.AsEnumerable()
            .Where(row => row.Field<int>("Age") > 25)
            .ToList();

        foreach (var row in filteredRows)
        {
            Console.WriteLine($"Name: {row["Name"]}, Age: {row["Age"]}");
        }
    }

    static DataTable GetSampleDataTable()
    {
        DataTable table = new DataTable();
        table.Columns.Add("Name", typeof(string));
        table.Columns.Add("Age", typeof(int));

        table.Rows.Add("Alice", 28);
        table.Rows.Add("Bob", 22);
        table.Rows.Add("Charlie", 30);
        table.Rows.Add("David", 25);

        return table;
    }
}

1. 排序(Sorting)

var sortedRows = table.AsEnumerable()
    .OrderBy(row => row.Field<int>("Age"))
    .ToList();

foreach (var row in sortedRows)
{
    Console.WriteLine($"Name: {row["Name"]}, Age: {row["Age"]}");
}

2. 投影(Projection)

var projectedData = table.AsEnumerable()
    .Select(row => new
    {
        Name = row.Field<string>("Name"),
        Age = row.Field<int>("Age")
    })
    .ToList();

foreach (var item in projectedData)
{
    Console.WriteLine($"Name: {item.Name}, Age: {item.Age}");
}

3. 分組(Grouping)

var groupedData = table.AsEnumerable()
    .GroupBy(row => row.Field<int>("Age") / 10 * 10)
    .Select(group => new
    {
        AgeGroup = $"{group.Key}-{group.Key + 9}",
        Count = group.Count()
    })
    .ToList();

foreach (var group in groupedData)
{
    Console.WriteLine($"Age Group: {group.AgeGroup}, Count: {group.Count}");
}

4. 比較式

4-1 等於(Equal)

var equalRows = table.AsEnumerable()
    .Where(row => row.Field<string>("Name") == "Alice")
    .ToList();

4-2 大於等於

var greaterThanOrEqualRows = table.AsEnumerable()
    .Where(row => row.Field<int>("Age") >= 25)
    .ToList();

4-3 多條件

var multipleConditions = table.AsEnumerable()
    .Where(row => row.Field<string>("Name") == "Alice" && row.Field<int>("Age") > 25)
    .ToList();

4-4 日期

DateTime targetDate = new DateTime(1990, 1, 1);

var dateComparison = table.AsEnumerable()
    .Where(row => row.Field<DateTime>("Birthdate") >= targetDate)
    .ToList();

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