Join-Object

Combines two object lists based on a related property between them.

Syntax

    [-LeftObject <Object>]
    [-RightObject <Object>]
    [-Discern <String[]>]
    [-Property <Object>]
    [-Where <ScriptBlock>]
    [-JoinType <String> = 'Inner']
    [-ValueName <String> = '<Value>']
    [<CommonParameters>]

    [-LeftObject <Object>]
    [-RightObject <Object>]
    [-On <Array> = @()]
    [-Equals <Array> = @()]
    [-Discern <String[]>]
    [-Property <Object>]
    [-Where <ScriptBlock>]
    [-JoinType <String> = 'Inner']
    [-ValueName <String> = '<Value>']
    [-Strict]
    [-MatchCase]
    [<CommonParameters>]

    [-LeftObject <Object>]
    [-RightObject <Object>]
    [-Using <ScriptBlock>]
    [-Discern <String[]>]
    [-Property <Object>]
    [-Where <ScriptBlock>]
    [-JoinType <String> = 'Inner']
    [-ValueName <String> = '<Value>']
    [<CommonParameters>]

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:

• An intuitive idiomatic PowerShell syntax
• SQL like joining features
• Smart property merging
• Predefined join commands for updating, merging and specific join types
• Well defined pipeline for the (left) input objects and output objects (streaming preserves memory)
• Performs about twice as fast as Compare-Object on large object lists
• Supports a list of (custom) objects, strings or primitives and dictionaries (e.g. hash tables) and data tables for input
• Smart properties and calculated property expressions
• Custom relation expressions
• Module (Install-Module -Name JoinModule) or (dot-sourcing) Script version (Install-Script -Name Join)
• Supports PowerShell for Windows (5.1) and PowerShell Core

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 objects
• LeftJoin-Object (Alias LeftJoin), combines the related objects and adds the rest of the left objects
• RightJoin-Object (Alias RightJoin), combines the related objects and adds the rest of the right objects
• OuterJoin-Object (Alias OuterJoin), returns the symmetric difference of the unrelated objects
• FullJoin-Object (Alias FullJoin), combines the related objects and adds the rest of the left and right objects
• CrossJoin-Object (Alias CrossJoin), combines each left object with each right object
• Update-Object (Alias Update), updates the left object with the related right object
• Merge-Object (Alias Merge), updates the left object with the related right object and adds the rest of the new (unrelated) right objects
• Get-Difference (Alias Differs), returns the symmetric different objects and their properties

Examples

Example 1: Common (inner) join

The following example will show an inner join based on the country property.
Given the following object lists:

 $Employee

Id Name    Country Department  Age ReportsTo
-- ----    ------- ----------  --- ---------
 1 Aerts   Belgium Sales        40         5
 2 Bauer   Germany Engineering  31         4
 3 Cook    England Sales        69         1
 4 Duval   France  Engineering  21         5
 5 Evans   England Marketing    35
 6 Fischer Germany Engineering  29         4

 $Department

Name        Country
----        -------
Engineering Germany
Marketing   England
Sales       France
Purchase    France


 $Employee |Join $Department -On Country |Format-Table

Id Name                   Country Department  Age ReportsTo
-- ----                   ------- ----------  --- ---------
 2 {Bauer, Engineering}   Germany Engineering  31         4
 3 {Cook, Marketing}      England Sales        69         1
 4 {Duval, Sales}         France  Engineering  21         5
 4 {Duval, Purchase}      France  Engineering  21         5
 5 {Evans, Marketing}     England Marketing    35
 6 {Fischer, Engineering} Germany Engineering  29         4

Example 2: Full join overlapping column names

The example below does a full join of the tables mentioned in the first example based on the department name and splits the duplicate (country) names over differend properties.

 $Employee |InnerJoin $Department -On Department -Equals Name -Discern Employee, Department |Format-Table

Id Name    EmployeeCountry DepartmentCountry Department  Age ReportsTo
-- ----    --------------- ----------------- ----------  --- ---------
 1 Aerts   Belgium         France            Sales        40         5
 2 Bauer   Germany         Germany           Engineering  31         4
 3 Cook    England         France            Sales        69         1
 4 Duval   France          Germany           Engineering  21         5
 5 Evans   England         England           Marketing    35
 6 Fischer Germany         Germany           Engineering  29         4

Example 3: merge a table with updates

This example merges the following $Changes list into the $Employee list of the first example.

 $Changes

Id Name    Country Department  Age ReportsTo
-- ----    ------- ----------  --- ---------
 3 Cook    England Sales        69         5
 6 Fischer France  Engineering  29         4
 7 Geralds Belgium Sales        71         1

 # Apply the changes to the employees
 $Employee |Merge $Changes -On Id |Format-Table

Id Name    Country Department  Age ReportsTo
-- ----    ------- ----------  --- ---------
 1 Aerts   Belgium Sales        40         5
 2 Bauer   Germany Engineering  31         4
 3 Cook    England Sales        69         5
 4 Duval   France  Engineering  21         5
 5 Evans   England Marketing    35
 6 Fischer France  Engineering  29         4
 7 Geralds Belgium Sales        71         1

Example 4: Self join

This example shows a (self)join where each employee is connected with another employee on the country.

 $Employee | Join -On Country -Discern *1,*2 |Format-Table *

Id1 Id2 Name1   Name2   Country Department1 Department2 Age1 Age2 ReportsTo1 ReportsTo2
--- --- -----   -----   ------- ----------- ----------- ---- ---- ---------- ----------
  2   6 Bauer   Fischer Germany Engineering Engineering   31   29          4          4
  3   5 Cook    Evans   England Sales       Marketing     69   35          1
  5   3 Evans   Cook    England Marketing   Sales         35   69                     1
  6   2 Fischer Bauer   Germany Engineering Engineering   29   31          4          4

Example 5: Join a scalar array

This example adds an Id to the department list.
note that the default column name of (nameless) scalar array is <Value> this will show when the -ValueName parameter is ommited.

 1..9 |Join $Department -ValueName Id

Id Name        Country
-- ----        -------
 1 Engineering Germany
 2 Marketing   England
 3 Sales       France
 4 Purchase    France

Example 6: Transpose arrays

The following example, the join-Object cmdlet (... |Join) joins multiple arrays to a collection array.
The Foreach-Object cmdlet iterates over the rows and the -Join operator concatinates the item collections

 $a = 'a1', 'a2', 'a3', 'a4'
 $b = 'b1', 'b2', 'b3', 'b4'
 $c = 'c1', 'c2', 'c3', 'c4'
 $d = 'd1', 'd2', 'd3', 'd4'

 $a |Join $b |Join $c |Join $d |% { $_ -Join '|' }

a1|b1|c1|d1
a2|b2|c2|d2
a3|b3|c3|d3
a4|b4|c4|d4

Example 7: Arrays to objects

This example will change the collections of the previous example into objects with named properties.

 $a |Join $b |Join $c |Join $d -Name a, b, c, d

a  b  c  d
-  -  -  -
a1 b1 c1 d1
a2 b2 c2 d2
a3 b3 c3 d3
a4 b4 c4 d4

Parameter

-LeftObject <>

The left object list, usually provided through the pipeline, to be joined.

Note: a self-join on the LeftObject list will be performed if the RightObject is omitted.

Type:
Mandatory:	False
Position:	Named
Default value:
Accept pipeline input:
Accept wildcard characters:	False

-RightObject <>

The right object list, provided by the first argument, to be joined.

Note: a self-join on the RightObject list will be performed if the LeftObject is omitted.

Type:
Mandatory:	False
Position:	Named
Default value:
Accept pipeline input:
Accept wildcard characters:	False

-On <>

The -On parameter defines which objects should be joined together.
If the -Equals parameter is omitted, the value(s) of the properties listed by the -On parameter should be equal at both sides in order to join the left object with the right object.
If the -On parameter contains an expression, the expression will be evaluted where $_, $PSItem and $Left contains the currect object. The result of the expression will be compared to right object property defined by the -Equals parameter.

Note 1: The list of properties defined by the -On parameter will be complemented with the list of properties defined by the -Equals parameter and vice versa.

Note 2: Related properties will be merged to a single property by default (see also the -Property parameter).

Note 3: If the -On and the -Using parameter are omitted, a side-by-side join is returned unless OuterJoin is performed where the default -On parameter value is * (all properties).

Note 4: if the left object is a scalar array, the -On parameters is used to name the scalar array

Type:
Mandatory:	False
Position:	Named
Default value:	@()
Accept pipeline input:
Accept wildcard characters:	False

-Using <>

Any conditional expression that requires to evaluate to true in order to join the left object with the right object.

The following variables are exposed for a (ScriptBlock) expression:

• $_: iterates each property name
• $Left: a hash table representing the current left object (each self-contained -LeftObject). The hash table will be empty (@{}) in the outer part of a left join or full join.
• $LeftIndex: the index of the left object ($Null in the outer part of a right- or full join)
• $Right: a hash table representing the current right object (each self-contained -RightObject) The hash table will be empty (@{}) in the outer part of a right join or full join.
• $RightIndex: the index of the right object ($Null in the outer part of a left- or full join)

Note 1: The -Using parameter has the most complex comparison possibilities but is considerable slower than the -On parameter.

Note 2: The -Using parameter cannot be used with the -On parameter.

Type:
Mandatory:	False
Position:	Named
Default value:
Accept pipeline input:
Accept wildcard characters:	False

-Equals <>

If the -Equals parameter is supplied, the value(s) of the left object properties listed by the -On parameter should be equal to the value(s)of the right object listed by the -Equals parameter in order to join the left object with the right object.
If the -Equals parameter contains an expression, the expression will be evaluted where $_, $PSItem and $Right contains the currect object. The result of the expression will be compared to left object property defined by the -On parameter.

Note 1: The list of properties defined by the -Equal parameter will be complemented with the list of properties defined by the -On parameter and vice versa. This means that by default value of the -Equals parameter is equal to the value supplied to the -On parameter

Note 2: A property will be omitted in the results if it exists on both sides and if the property at the other side is related to another property.

Note 3: The -Equals parameter can only be used with the -On parameter.

Note 4: if the right object is a scalar array, the -Equals parameters is used to name the scalar array

Type:
Mandatory:	False
Position:	Named
Default value:	@()
Accept pipeline input:
Accept wildcard characters:	False

-Discern <>

By default unrelated properties with the same name will be collected in a single object property. The -Discern parameter (alias -NameItems) defines how to rename the object properties and divide them over multiple properties. If a given name pattern contains an asterisks (*), the asterisks will be replaced with the original property name. Otherwise, the property name for each property item will be prefixed with the given name pattern.

The property collection of multiple (chained) join commands can be divided in once from the last join command in the change. The rename patterns are right aligned, meaning that the last renamed pattern will be applied to the last object joined. If there are less rename patterns than property items, the rest of the (left most) property items will be put in a fixed array under the original property name.

Note 1: Only properties with the same name on both sides will not be renamed.

Note 2: Related properties (with an equal value defined by the -On parameter) will be merged to a single item.

Type:
Mandatory:	False
Position:	Named
Default value:
Accept pipeline input:
Accept wildcard characters:	False

-Property <>

A hash table or list of property names (strings) and/or hash tables that define a new selection of property names and values

Hash tables should be in the format @{<PropertyName> = <Expression>} where the <Expression> is a ScriptBlock or a smart property (string) and defines how the specific left and right properties should be merged. See the -Using parameter for available expression variables.

The following smart properties are available:

• A general property: '', where <Property Name> represents the property name of the left and/or right property, e.g. @{ MyProperty = 'Name' }. If the property exists on both sides, an array holding both values will be returned. In the outer join, the value of the property will be $Null. This smart property is similar to the expression: @{ MyProperty = { @($Left['Name'], $Right['Name']) } }
• A general wildcard property: '*', where * represents the property name of the current property, e.g. MyProperty in @{ MyProperty = '*' }. If the property exists on both sides:

• and the properties are unrelated, an array holding both values will be returned
• and the properties are related to each other, the (equal) values will be merged in one property value
• and the property at the other side is related to an different property, the property is omitted The argument: -Property *, will apply a general wildcard on all left and right properties.

• A left property: ;Left.<Property Name>', or right property: ;Right.<Property Name>', where <Property Name> represents the property name of the either the left or right property. If the property doesn't exist, the value of the property will be $Null.
• A left wildcard property: 'Left.*', or right wildcard property: Right.*, where * represents the property name of the current the left or right property, e.g. MyProperty in @{ MyProperty = 'Left.*' }. If the property doesn't exist (in an outer join), the property with the same name at the other side will be taken. If the property doesn't exist on either side, the value of the property will be $Null. The argument: -Property 'Left.*', will apply a left wildcard property on all the left object properties.

If the -Property parameter and the -Discern parameter are omitted, a general wildcard property is applied on all the left and right properties.

The last defined expression or smart property will overrule any previous defined properties.

Type:
Mandatory:	False
Position:	Named
Default value:
Accept pipeline input:
Accept wildcard characters:	False

-Where <>

An expression that defines the condition to be met for the objects to be returned. See the -Using parameter for available expression variables.

Type:
Mandatory:	False
Position:	Named
Default value:
Accept pipeline input:
Accept wildcard characters:	False

-JoinType <>

Defines which unrelated objects should be included (see: Description). Valid values are: Inner, Left, Right, Full or Cross. The default is Inner.

Note: it is recommended to use the related proxy commands (... |<JoinType>-Object ...) instead.

Type:
Mandatory:	False
Position:	Named
Default value:	'Inner'
Accept pipeline input:
Accept wildcard characters:	False

-ValueName <>

Defines the name of the added property in case a scalar array is joined with an object array. The default property name for each scalar is: <Value>.

Note: if two scalar (or collection) arrays are joined, an array of (psobject) collections is returned. Each collection is a concatenation of the left item (collection) and the right item (collection).

Type:
Mandatory:	False
Position:	Named
Default value:	''
Accept pipeline input:
Accept wildcard characters:	False

-Strict <>

If the -Strict switch is set, the comparison between the related properties defined by the -On Parameter (and the -Equals parameter) is based on a strict equality (both type and value need to be equal).

Type:
Mandatory:	False
Position:	Named
Default value:
Accept pipeline input:
Accept wildcard characters:	False

-MatchCase <>

If the -MatchCase (alias -CaseSensitive) switch is set, the comparison between the related properties defined by the -On Parameter (and the -Equals parameter) will case sensitive.

Type:
Mandatory:	False
Position:	Named
Default value:
Accept pipeline input:
Accept wildcard characters:	False

Related Links

• https://www.powershellgallery.com/packages/Join
• https://www.powershellgallery.com/packages/JoinModule
• https://github.com/iRon7/Join-Object