在PowerShell中查询列表LINQ样式

是否有一种方法可以从$CODE中选择distinct并选择类型为1的对象？如何将LINQ与PowerShell一起使用？

对于distinct，请使用别名为Select的Select Object cmdlet，以使用唯一参数进行选择，例如：

add-type -Language CSharpVersion3 -TypeDefinition @"
    public class pack_code
    {
        public pack_code() {}

        public string code { get; set; }
        public string type { get; set; }
    }
"@

$a = New-Object pack_code
$a.code = "3"
$a.type = "5"
$b = New-Object pack_code
$b.code = "2"
$b.type = "5"
$c = New-Object pack_code
$c.code = "2"
$c.type = "5"
$d = New-Object pack_code
$d.code = "1"
$d.type = "1"

$codes = New-Object 'System.Collections.Generic.List[object]'
$codes.add($a)
$codes.add($b)
$codes.add($c)
$codes.add($d)

要进行筛选，请使用别名为Where和？的Where-Object cmdlet：

至于LINQ，您不能在PowerShell中使用LINQ运算符，因为PowerShell不支持调用通用.NET方法或静态扩展方法，这两种方法对LINQ都至关重要

---

编者按：PSv3+现在确实支持这些东西。

基思说的。另外，更改了C中的构造函数，并在Sort cmdlet上使用了-Unique参数

PS> $codes | where {$_.Type -eq '1'}

---

简单的问题，简单的回答：

Add-Type -Language CSharpVersion3 -TypeDefinition @"
    public class pack_code
    {
        public pack_code(string code, string type) {
            this.code=code;
            this.type=type;
        }

        public string code { get; set; }
        public string type { get; set; }
    }
"@

$codes = New-Object 'System.Collections.Generic.List[object]'
$codes.Add( ( New-Object pack_code 3, 5 ))
$codes.Add( ( New-Object pack_code 2, 5 ))
$codes.Add( ( New-Object pack_code 2, 5 ))
$codes.Add( ( New-Object pack_code 1, 1 ))
$codes.Add( ( New-Object pack_code 2, 2 ))
$codes.Add( ( New-Object pack_code 2, 1 ))
$codes.Add( ( New-Object pack_code 2, 1 ))

$codes | sort code, type -Unique | where {$_.type -eq 1}

并向您展示PowerShell与.Distinct和.Where LINQ方法的惯用类比

在PowerShell v3或更高版本中，您现在可以使用LINQ

下面的解决方案演示了LINQ可以用来解决您的问题，但也表明这样做有点麻烦，并且可能只在您需要高级查询功能和/或性能问题时才值得付出努力

有关如何使用PowerShell中的LINQ的一般概述，请参见我的。

---

这是有希望的，但正如编写的代码那样，您的代码将无法工作，因为它缺少用于识别重复[pack_code]实例的自定义比较逻辑；换句话说：你的电话是有效的禁止操作。

Add-Type -Language CSharpVersion3 -TypeDefinition @"
    public class pack_code
    {
        public pack_code(string code, string type) {
            this.code=code;
            this.type=type;
        }

        public string code { get; set; }
        public string type { get; set; }
    }
"@

$codes = New-Object 'System.Collections.Generic.List[object]'
$codes.Add( ( New-Object pack_code 3, 5 ))
$codes.Add( ( New-Object pack_code 2, 5 ))
$codes.Add( ( New-Object pack_code 2, 5 ))
$codes.Add( ( New-Object pack_code 1, 1 ))
$codes.Add( ( New-Object pack_code 2, 2 ))
$codes.Add( ( New-Object pack_code 2, 1 ))
$codes.Add( ( New-Object pack_code 2, 1 ))

$codes | sort code, type -Unique | where {$_.type -eq 1}

[Linq.Enumerable]::Distinct($codes)

# Create the type whose instances will make up the list to filter.
# Make it implement IEquatable<T> with custom comparison logic that
# compares property values so that the .Distinct() LINQ method works correctly.
Add-Type -TypeDefinition @"

  public class pack_code : System.IEquatable<pack_code>
  {
      public string code { get; set; }
      public string type { get; set; }

      // IEquatable<T> interface implementation

      // Test equality of this object with another of the same type.
      public bool Equals(pack_code other) {
        // Note: Normally, you'd need to deal with the case of other == null as well.
        return this.code == other.code && this.type == other.type;
      }

      // If Equals() returns true for a pair of objects  
      // then GetHashCode() must return the same value for these objects.         
      public override int GetHashCode() {
        return this.code.Length + this.type.Length;
      }
  }

"@

# Create the list to filter.
# Note:
#  * Despite not having a constructor for [pack_code], PowerShell is smart
#    enough to construct an instance from a cast from a hashtable that contains
#    entries whose names match the settable [pack_code] properties.
#  * The array of [pack_code] instances is then cast to the list type.
#  * The list contains 3 objects of type 1, but only 2 distinct ones.
$codes = [System.Collections.Generic.List[pack_code]] (
           [pack_code] @{code = '2'; type = '1'},
           [pack_code] @{code = '3'; type = '5'},
           [pack_code] @{code = '2'; type = '1'},
           [pack_code] @{code = '1'; type = '1'}
         )

# Invoke the LINQ methods as static methods of the 
# [System.Linq.Enumerable] type to
# return all distinct objects whose type property is ‘1’.
# Note that the result will be an *iterator*; if you want a
# static array, wrap the call in [Linq.Enumerable]::ToArray(...)
[Linq.Enumerable]::Where(
  [Linq.Enumerable]::Distinct($codes),
  [Func[pack_code, bool]] { $Args[0].type -eq '1' }
)