读取 CSV 文件并逐步添加 Powershell 中特定列的值答案

【问题标题】：Read a CSV file and Progressively AddUp the values of a Specific column in Powershell读取 CSV 文件并逐步添加 Powershell 中特定列的值
【发布时间】：2021-02-03 19:16:38
【问题描述】：

我想使用 powershell 脚本读取 CSV 文件中特定列的所有行。然后逐步添加值直到当前行，然后在新列中更新总和。

例如：在下面的示例中，我想读取 COLUMNB 列中的所有值，然后逐步添加它并在 PROG_COLB 中更新它同样，我想为 COLUMNC 做这件事

CSV 文件示例：

"RANK","COLUMNB","COLUMNC"
"5","510","10"
"4","500","60"
"3","120","100"
"0","600","200"
"-1","1000","40"

预期输出：

"RANK","COLUMNB","COLUMNC","PROG_COLB","PROG_COLC"
"5","510","10","510","10"
"4","500","60","1010","70"
"3","120","100","1130","170"
"0","600","200","1730","370"
"-1","1000","40","2730","410"

我尝试了几件事，但无法获得预期的输出，我能够读取特定列，并且设法将其放入哈希表中，然后我被卡住了。任何关于如何解决这个谜题的建议都会有很大帮助。

$csv =Import-Csv .\stats.csv 
$hash_COLB = @{}
$hash_COLC = @{}
foreach($item in $csv)
{
[int]$prog_COLB=[int]$prog_COLB+[int]$item.COLUMNB
[int]$prog_COLC=[int]$prog_COLC+[int]$item.COLUMNC
$hash_COLB.add($item.RANK,$prog_COLB)
$hash_COLC.add($item.RANK,$prog_COLC)
}

$hash_COLB
$hash_COLC

【问题讨论】：

标签： powershell

【解决方案1】：

您可以为 COLUMNB 和 COLUMNC 中的值的运行计数创建两个变量。

$runningCount_B = 0
$runningCount_C = 0
$result = Import-Csv -Path 'D:\Test\sample.csv' | ForEach-Object {
    $runningCount_B += [int]$_.COLUMNB
    $runningCount_C += [int]$_.COLUMNC
    # output a new object with all columns from the original, and added running counts
    $_ | Select-Object *, @{Name = 'PROG_COLB'; Expression = {$runningCount_B}}, 
                          @{Name = 'PROG_COLC'; Expression = {$runningCount_C}}
}

# output on console screen
$result | Format-Table -AutoSize

# output to new CSV
$result | Export-Csv -Path 'D:\Test\new_sample.csv' -NoTypeInformation

输出为 CSV：

"RANK","COLUMNB","COLUMNC","PROG_COLB","PROG_COLC"
"5","510","10","510","10"
"4","500","60","1010","70"
"3","120","100","1130","170"
"0","600","200","1730","370"
"-1","1000","40","2730","410"

【讨论】：

【解决方案2】：

最直接 (IMO) 且易于阅读的解决方案使用 ForEach-Object 迭代行并输出具有计算出的新行的 PSCustomObject。

$sumColB = 0
$sumColC = 0

$newCsv = $csv | ForEach-Object {
    $sumColB += $_.COLUMNB
    $sumColC += $_.COLUMNC

    # This is the output of this loop iteration. PowerShell automatically adds it to $newCsv.
    [PSCustomObject]@{
        RANK      = $_.RANK
        COLUMNB   = $_.COLUMNB
        COLUMNC   = $_.COLUMNC
        PROG_COLB = $sumColB
        PROG_COLC = $sumColC
    }
}

另一种方式是Select-Object与calculated properties一起使用，可读性较差，但具有可重复使用的优势。

Function Get-ColumnSum( [ref] $var, $columnName ) { 
    $var.Value += $_.$columnName   # Add the value of the column named by $columnName
    $var.Value                     # output
}

$sumB = 0
$sumC = 0

$newCsv = $csv | Select-Object *, 
                   @{ name = 'PROG_COLB'; expression = { Get-ColumnSum ([ref] $sumB) COLUMNB } }, 
                   @{ name = 'PROG_COLC'; expression = { Get-ColumnSum ([ref] $sumC) COLUMNC } }

首先我们定义一个函数Get-ColumnSum，它将给定列的值累加到一个通过引用传递的变量中，并输出当前的总和。

然后在Select-Object 调用中，我们从计算列的脚本块中调用此函数。

由于 PowerShell 范围规则，必须通过引用传递变量。如果您在嵌套范围内修改变量，则只会修改该变量的副本。通过传递引用我们可以直接修改给定的变量。

【讨论】：