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I'm fairly new to Powershell, and am wondering if someone knows of any better way to accomplish the following example problem.
I have an array of mappings from IP address to host-name. This represents a list of active DHCP leases:
PS H:\> $leases IP Name -- ---- 192.168.1.1 Apple 192.168.1.2 Pear 192.168.1.3 Banana 192.168.1.99 FishyPC I have another array of mappings from MAC address to IP address. This represents a list of IP reservations:
PS H:\> $reservations IP MAC -- --- 192.168.1.1 001D606839C2 192.168.1.2 00E018782BE1 192.168.1.3 0022192AF09C 192.168.1.4 0013D4352A0D For convenience, I was able to produce a third array of mappings from MAC address to IP address and host name using the following code. The idea is that $reservations should get a third field, "Name", which is populated whenever there's a matching "IP" field:
$reservations = $reservations | foreach { $res = $_ $match = $leases | where {$_.IP -eq $res.IP} | select -unique if ($match -ne $NULL) { "" | select @{n="IP";e={$res.IP}}, @{n="MAC";e={$res.MAC}}, @{n="Name";e={$match.Name}} } } The desired output is something like this:
PS H:\> $ideal IP MAC Name -- --- ---- 192.168.1.1 001D606839C2 Apple 192.168.1.2 00E018782BE1 Pear 192.168.1.3 0022192AF09C Banana 192.168.1.4 0013D4352A0D Is there any better way of doing this?
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If you want to join arrays in Powershell, especially if you don't know if one or more of the objects you are joining are arrays or single objects, combine them with the addition '+' operator and cast the first item as an array.
The join operator concatenates a set of strings into a single string. The strings are appended to the resulting string in the order that they appear in the command.
In PowerShell, string concatenation is primarily achieved by using the “+” operator. There are also other ways like enclosing the strings inside double quotes, using a join operator, or using the -f operator. $str1="My name is vignesh."
After 1.5 years, the cmdlet I had pasted in the original answer has undergone so many updates that it has become completely outdated. Therefore I have replaced the code and the ReadMe with a link to the latest version.
Combines two object lists based on a related property between them.
Description
Combines properties from one or more objects. It creates a set that can be saved as a new object or used as it is. An object join is a means for combining properties from one (self-join) or more object lists by using values common to each.
Main features
The Join-Object cmdlet reveals the following proxy commands with their own (-JoinType and -Property) defaults:
InnerJoin-Object (Alias InnerJoin or Join), combines the related objectsLeftJoin-Object (Alias LeftJoin), combines the related objects and adds the rest of the left objectsRightJoin-Object (Alias RightJoin), combines the related objects and adds the rest of the right objectsFullJoin-Object (Alias FullJoin), combines the related objects and adds the rest of the left and right objectsCrossJoin-Object (Alias CrossJoin), combines each left object with each right objectUpdate-Object (Alias Update), updates the left object with the related right objectMerge-Object (Alias Merge), updates the left object with the related right object and adds the rest of the new (unrelated) right objectsThe full ReadMe (and source code) is available from GitHub: https://github.com/iRon7/Join-Object
There are two versions of this Join-Object cmdlet (both versions supply the same functionality):
Install-Module -Name JoinModule Install-Script -Name Join (or rename the Join.psm1 module to a Join.ps1 script file)
and invoked the script by dot sourcing:
. .\Join.ps1 To answer the actual example in the question:
$reservations |LeftJoin $leases -On IP IP MAC Name -- --- ---- 192.168.1.1 001D606839C2 Apple 192.168.1.2 00E018782BE1 Pear 192.168.1.3 0022192AF09C Banana 192.168.1.4 0013D4352A0D A little word on performance measuring:
The PowerShell pipeline is designed to stream objects (which safes memory), meaning that both¹ lists of input objects usually aren't (shouldn't be) resident in memory. Normally they are retrieved from somewhere else (i.e. a remote server, a disk). Also, the output usually matters where linq solutions are fast but might easily put you on the wrong foot in drawing conclusions because linq literally defers the execution (lazy evaluation), see also: fastest way to get a uniquely index item from the property of an array.
In other words, if it comes to (measuring) performance in PowerShell, it is important to look to the complete end-to-end solution, which is more likely to look something like:
import-csv .\reservations.csv |LeftJoin (import-csv .\leases.csv) -On IP |Export-Csv .\results.csv (1) Note: unfortunately, there is no easy way to build two parallel input streams (see: #15206 Deferred input pipelines)
More examples can be found in the related Stackoverflow questions at:
paste (i.e., horizontal file concatenation)?And in the Join-Object test script.
Please give a 👍 if you support the proposal to Add a Join-Object cmdlet to the standard PowerShell equipment (#14994)
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Here's a simple example using a hashtable. With big arrays, this turns out to be faster.
$leases = 'IP,Name 192.168.1.1,Apple 192.168.1.2,Pear 192.168.1.3,Banana 192.168.1.99,FishyPC' | convertfrom-csv $reservations = 'IP,MAC 192.168.1.1,001D606839C2 192.168.1.2,00E018782BE1 192.168.1.3,0022192AF09C 192.168.1.4,0013D4352A0D' | convertfrom-csv $hashRes=@{} foreach ($resRecord in $reservations) { $hashRes[$resRecord.IP] = $resRecord } $leases | foreach { $other = $hashRes[$_.IP] [pscustomobject]@{IP=$_.IP MAC=$other.MAC Name=$_.name} } IP MAC Name -- --- ---- 192.168.1.1 001D606839C2 Apple 192.168.1.2 00E018782BE1 Pear 192.168.1.3 0022192AF09C Banana 192.168.1.99 FishyPC If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
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