Question

我写了一个函数和过滤器来分析CSV文件的内容。

创建列对象管道的函数：

function Analyze {

        [CmdletBinding()]
        Param(
          [String]
          $File
        )

        # get column headers from CSV; enumerate
        $Headers = (Get-Content $File | Select-Object -First 1).Split(',')
        $Headers | ForEach-Object {

          # create an object that represents each column; initialize values
          $Column = [PsCustomObject]@{'Name'=$_;'Measurements'=@()}

          # add to pipeline
          $Column
        }

}

过滤以计算每列内容的最小值：

filter Min {

    Param(
        [string]$File
    )

    # create Logparser query
    $Query = "SELECT Min($($_.Name)) AS Minimum FROM '$File'"

    # excute query; return results as XML
    [xml] $xml = & logparser $Query -stats:off -o:xml

    # create object to contain measurement and its value
    $Measurement=[PsCustomObject]@{'Name'='Minimum';Value=$xml.root.row.Minimum.Trim()}

    # add to collection and return to pipeline
    $_.Measurements+=$Measurement
    $_

}

过滤以计算每列内容的最小值：

filter Max {

    Param(
        [string]$File
    )

    # create Logparser query
    $Query = "SELECT Max($($_.Name)) AS Maximum FROM '$File'"

    # excute query; return results as XML
    [xml] $xml = & logparser $Query -stats:off -o:xml

    # create object to contain measurement and its value
    $Measurement=[PsCustomObject]@{'Name'='Maximum';Value=$xml.root.row.Maximum.Trim()}

    # add to collection and return to pipeline
    $_.Measurements+=$Measurement
    $_

}

用法：

pushd C:\users\<user>\Desktop
$File = '.\d.csv'
Analyze -File $File | Min -File $File | Max -File $File
popd

有没有办法构建过滤器，以便我可以这样称呼它：

pushd C:\users\<user>\Desktop
Analyze -File '.\d.csv' | Min | Max
popd

Answer 1

基于@Mathias R. Jessen的评论，我重构了函数和过滤器：

Data

需要禁用过滤器的管道：

function Analyze {

    [CmdletBinding()]
    Param(
        [Parameter(Mandatory=$True,Position=1)]
        [alias('f')]
        [String]
        $File,

        [Switch] $Min,
        [Switch] $Max,
        [Switch] $Top
    )

    # get column headers from CSV; enumerate
    $Included = (Get-Content $File | Select-Object -First 1).Split(',')

    $Included | ForEach-Object {

        # create a hash that represents each column; initialize values
        $Column = [PsCustomObject]@{'Name'=$_;'Measurements'=@()}

        # apply specified filter; pass object via pipeline
        if ($Min) { $Column | Min -File $File }
        if ($Max) { $Column | Max -File $File }
        if ($Top) { $Column | Top -File $File }

        # add to pipeline
        $Column

    }

}

用法：

filter Min {

    [Parameter(Mandatory=$True,Position=1)]
    [alias('f')]
    Param(
        [string]$File
    )

    $Query = "SELECT Min([$($_.Name)]) AS Minimum FROM '$File'"

    [xml] $xml = & logparser $Query -stats:off -o:xml
    $Measurement=[PsCustomObject]@{'Name'='Minimum';Value=$xml.root.row.Minimum.Trim()}

    $_.Measurements+=$Measurement

    # pipeline disabled; created multiple instances of Column object
    #$_

}

# similar changes to these filters
filter Max {}
filter Top {}

函数中指定的参数自动传递给过滤器

1 个答案: