我能够让您提出的代码工作，但它需要对代码和数据进行一些调整：
- 必须有一些额外的步骤将
rooms.csv 的students 列反序列化为对象集合。它似乎是一个 ScriptBlock，其计算结果为 HashTables 数组，但仍需要对 CSV 输入进行一些更改：
-
StartDate 和 EndDate 属性需要被引用并转换为 [DateTime]。
- 至少对于包含多个学生的房间，必须引用该值，以便
Import-Csv 不会将 , 分隔数组元素解释为附加列。
- 使用 CSV 作为中间格式的缺点是丢失了原始属性类型；导入后，所有内容都变为
[String]。有时出于效率目的需要转换回原始类型，有时为了使某些操作正常工作是绝对必要的。您可以在每次使用这些属性时进行转换，但我更喜欢在导入后立即转换一次。
随着这些变化rooms.csv 变成...
roomName, roomNo, students
room1, 1, "{@{StudentNo=111; StudentName='john smith'; StartDate=[DateTime] '2018-01-01T00:00:00'; EndDate=[DateTime] '2018-07-06T00:00:00'}}"
room2, 2, "{@{StudentNo=222; StudentName='jane doe'; StartDate=[DateTime] '2018-01-01T00:00:00'; EndDate=[DateTime] '2018-07-06T00:00:00'}}"
...脚本变成...
# Replace the [String] property "students" with an array of [HashTable] property "Students"
$rooms = Import-Csv rooms.csv `
| Select-Object `
-ExcludeProperty 'students' `
-Property '*', @{
Name = 'Students'
Expression = {
$studentsText = $_.students
$studentsScriptBlock = Invoke-Expression -Command $studentsText
$studentsArray = @(& $studentsScriptBlock)
return $studentsArray
}
}
# Replace the [String] property "StudentNo" with an [Int32] property of the same name
$students = Import-Csv students.csv `
| Select-Object `
-ExcludeProperty 'StudentNo' `
-Property '*', @{
Name = 'StudentNo'
Expression = { [Int32] $_.StudentNo }
}
$combined = $students `
| Select-Object -Property `
'StudentNo', `
'PreferredSurname', `
'PreferredFirstnames', `
'UPN', `
@{
Name = "roomName";
Expression = {
foreach ($r in $rooms)
{
if ($r.Students.StudentNo -contains $_.StudentNo)
{
return $r.roomName
}
}
#TODO: Return text indicating room not found?
}
}
这可能很慢的原因是因为您正在执行线性搜索 - 实际上是其中两个 - 针对每个学生对象；首先通过房间集合 (foreach)，然后通过每个房间的学生集合 (-contains)。这很快就会变成大量的迭代和相等比较，因为在当前学生未分配到的每个房间中，您都在迭代该房间的学生的整个集合，不断地迭代，直到您找到该学生的房间。
在执行线性搜索时可以进行的一个简单优化是对正在搜索的项目进行排序（在这种情况下，Students 属性将按每个学生的StudentNo 属性排序）...
# Replace the [String] property "students" with an array of [HashTable] property "Students"
$rooms = Import-Csv rooms.csv `
| Select-Object `
-ExcludeProperty 'students' `
-Property '*', @{
Name = 'Students'
Expression = {
$studentsText = $_.students
$studentsScriptBlock = Invoke-Expression -Command $studentsText
$studentsArray = @(& $studentsScriptBlock) `
| Sort-Object -Property @{ Expression = { $_.StudentNo } }
return $studentsArray
}
}
...然后当您搜索同一个集合时，如果您遇到的项目大于您正在搜索的项目，您就会知道该集合的其余部分不能可能包含您正在搜索的内容，您可以立即中止搜索...
@{
Name = "roomName";
Expression = {
foreach ($r in $rooms)
{
# Requires $room.Students to be sorted by StudentNo
foreach ($roomStudentNo in $r.Students.StudentNo)
{
if ($roomStudentNo -eq $_.StudentNo)
{
# Return the matched room name and stop searching this and further rooms
return $r.roomName
}
elseif ($roomStudentNo -gt $_.StudentNo)
{
# Stop searching this room
break
}
# $roomStudentNo is less than $_.StudentNo; keep searching this room
}
}
#TODO: Return text indicating room not found?
}
}
更好的是，通过排序集合，您还可以执行binary search，这比线性搜索要快*。 Array class 已经提供了一个BinarySearch static method，所以我们也可以用更少的代码来完成这个......
@{
Name = "roomName";
Expression = {
foreach ($r in $rooms)
{
# Requires $room.Students to be sorted by StudentNo
if ([Array]::BinarySearch($r.Students.StudentNo, $_.StudentNo) -ge 0)
{
return $r.roomName
}
}
#TODO: Return text indicating room not found?
}
}
然而，我解决这个问题的方法是使用[HashTable] 将StudentNo 映射到一个房间。构建[HashTable] 需要进行一些预处理，但这将在为学生检索房间时提供恒定时间的查找。
function GetRoomsByStudentNoTable()
{
$table = @{ }
foreach ($room in $rooms)
{
foreach ($student in $room.Students)
{
#NOTE: It is assumed each student belongs to at most one room
$table[$student.StudentNo] = $room
}
}
return $table
}
# Replace the [String] property "students" with an array of [HashTable] property "Students"
$rooms = Import-Csv rooms.csv `
| Select-Object `
-ExcludeProperty 'students' `
-Property '*', @{
Name = 'Students'
Expression = {
$studentsText = $_.students
$studentsScriptBlock = Invoke-Expression -Command $studentsText
$studentsArray = @(& $studentsScriptBlock)
return $studentsArray
}
}
# Replace the [String] property "StudentNo" with an [Int32] property of the same name
$students = Import-Csv students.csv `
| Select-Object `
-ExcludeProperty 'StudentNo' `
-Property '*', @{
Name = 'StudentNo'
Expression = { [Int32] $_.StudentNo }
}
$roomsByStudentNo = GetRoomsByStudentNoTable
$combined = $students `
| Select-Object -Property `
'StudentNo', `
'PreferredSurname', `
'PreferredFirstnames', `
'UPN', `
@{
Name = "roomName";
Expression = {
$room = $roomsByStudentNo[$_.StudentNo]
if ($room -ne $null)
{
return $room.roomName
}
#TODO: Return text indicating room not found?
}
}
您可以通过在导入 rooms.csv 的同时这样做来改善构建 $roomsByStudentNo 的影响...
# Replace the [String] property "students" with an array of [HashTable] property "Students"
$rooms = Import-Csv rooms.csv `
| Select-Object `
-ExcludeProperty 'students' `
-Property '*', @{
Name = 'Students'
Expression = {
$studentsText = $_.students
$studentsScriptBlock = Invoke-Expression -Command $studentsText
$studentsArray = @(& $studentsScriptBlock)
return $studentsArray
}
} `
| ForEach-Object -Begin {
$roomsByStudentNo = @{ }
} -Process {
foreach ($student in $_.Students)
{
#NOTE: It is assumed each student belongs to at most one room
$roomsByStudentNo[$student.StudentNo] = $_
}
return $_
}
*小型数组除外