Avoid Array Addition - Tip
This post is updated and replaced by Avoid-Array-Addition-Tip-update
Like many others, I’m a fan of PowerShell.tiPS by Daniel Schroeder (aka @deadlydog), and the other day a really nice tip submitted by: Santiago Squarzon appeared in my PowerShell console. The tip was so sweet that I just had to go ahead and expand the example and then used Measure-Command to test the benefit described by Santiago’s tip.
Firstly, the tip
# --------------------------- Avoid Array addition [Performance] ---------------------------
# Array addition is an expensive and inefficient operation and can usually be replaced by PowerShell explicit loop assignment.
# Use a `List<T>` instead in those cases when adding to a collection while looping is required.
Example:
# Array addition:
$items = @()
foreach ($i in 0..10) {
$items += $i
}
# Can be easily replaced with explicit assignment:
$items = foreach ($i in 0..10) {
$i
}
# And, when not possible, a List<T> is recommended:
$items = [System.Collections.Generic.List[int]]::new()
foreach ($i in 0..10) {
$items.Add($i)
}
More information: https://learn.microsoft.com/en-us/powershell/scripting/dev-cross-plat/performance/script-authoring-considerations#array-addition
Tip submitted by: Santiago Squarzon (santisq)
Expanding the example with Measure-Command
PowerShell is full of many great Commands Cmdlets and Modules, and one of my favourites is Measure-Command.
Measure-Command makes it very easy to assess the performance of your commands, and to test improvements. And that’s what I show in the example. I’ve wrapped the tip with Measure-Command to reveal how much faster the code gets when following that great tip.
Hope you like the goodies
$upperBound = 10000
Measure-Command {
# Array addition:
$items = @()
foreach ($i in 0..$upperBound) {
$items += $i
}
} | Select-Object TotalMilliseconds # TotalMilliseconds: 2076.1273
Measure-Command {
# Can be easily replaced with explicit assignment:
$items = foreach ($i in 0..$upperBound) {
$i
}
} | Select-Object TotalMilliseconds # TotalMilliseconds: 15.3416
Measure-Command {
# And, when not possible, a List<T> is recommended:
$items = [System.Collections.Generic.List[int]]::new()
foreach ($i in 0..$upperBound) {
$items.Add($i)
}
} | Select-Object TotalMilliseconds # TotalMilliseconds: 11.2543
TotalMilliseconds
-----------------
2076.1273 # Array addition
15.3416 # Explicit assignment
11.2543 # List<T>
Performance improvements
See What’s New in PowerShell 7.5 for some relevant additional info on this topic, where PowerShell 7.5-rc.1 has included PR#23901 from @jborean93 that improves the performance of the += operation for an array of objects.
Tip: there is a great example of performance improvements measurement at the same What’s New in PowerShell 7.5 link above.