在 PowerShell 上查找 Hashtable 的最小元素（值为 - DateTime）

Question

有一个视图的哈希表： 键（字符串）-值（日期时间）

必须在 Values (dateTime-s) 中找到最小值。无法找到通用方法来找到这样的值。唯一的办法就是

$first_file_date = $dates_hash.Values | Measure-Object -Minimum -Maximum
Get-Date ($first_file_date);

虽然我得到了结果 ($first_file_date)，但实际值转换为 GenericObjectMeasureInfo 类型，我无法将其转换回 DateTime 以进一步工作。

有什么想法吗？

Answer 1

您感兴趣的值存储在 Measure-Object 返回的对象的 Minimum 和 Maximum 属性中：

$measurement = $dates_hash.Values | Measure-Object -Minimum -Maximum

# Minimum/oldest datetime value is stored here
$measurement.Minimum

# Maximum/newest datetime value is stored here
$measurement.Maximum

如果您希望单个管道中的原始值，请使用 ForEach-Object 或 Select-Object：

$oldest = $dates_hash.Values | Measure-Object -Minimum | ForEach-Object -MemberName Minimum
# or 
$oldest = $dates_hash.Values | Measure-Object -Minimum | Select-Object -ExpandProperty Minimum

Answer 2

为此使用 Sort-Object:

$dates_hash = @{
    "a" = (Get-Date).AddMinutes(4)    
    "b" = (Get-Date).AddMinutes(5)    
    "c" = (Get-Date).AddMinutes(2)    
    "d" = (Get-Date).AddMinutes(5)    
    "e" = (Get-Date).AddMinutes(1)    
    "f" = (Get-Date).AddMinutes(6)    
    "g" = (Get-Date).AddMinutes(8)    
}

$first_file_date = $dates_hash.Values | Sort-Object | Select-Object -First 1

或者如果你想要整个对象：

$first_file = $dates_hash.GetEnumerator() | Sort-Object -Property "Value" | Select-Object -First 1

Answer 3

用基于 LINQ 的替代解决方案补充：

# Sample hashtable.
$hash = @{
  foo = (Get-Date)
  bar = (Get-Date).AddDays(-1)
}

# Note that the minimum is sought among the hash's *values* ([datetime] instances)
# The [datetime[] cast is required to find the appropriate generic overload.
[Linq.Enumerable]::Min([datetime[]] $hash.Values)

使用 LINQ from PowerShell is generally cumbersome, unfortunately (see ). GitHub proposal #2226 提出改进建议。

在 PowerShell 上查找 Hashtable 的最小元素（值为 - DateTime）

Find the min element of Hashtable (Values are - DateTime) on PowerShell

powershell

hashtable