about_Calculated_Properties
Short description
PowerShell provides the ability to dynamically add new properties and alter the formatting of objects output to the pipeline.
Long description
Several PowerShell cmdlets transform, group, or process input objects into output objects using parameters that allow the addition of new properties to those output objects. You can use these parameters to generate new, calculated properties on output objects based on the values of input objects. The calculated property is defined by a hashtable containing key-value pairs that specify the name of the new property, an expression to calculate the value, and optional formatting information.
Supported cmdlets
The following cmdlets support calculated property values for the Property
parameter. The Format-* cmdlets also support calculated values for the
GroupBy parameter.
The following list itemizes the cmdlets that support calculated properties and the key-value pairs that each cmdlet supports.
Compare-Objectexpression
ConvertTo-Htmlname/label- optional (added in PowerShell 6.x)expressionwidth- optionalalignment- optional
Format-Customexpressiondepth- optional
Format-Listname/label- optionalexpressionformatstring- optional
This same set of key-value pairs also apply to calculated property values passed to the GroupBy parameter for all
Format-*cmdlets.Format-Tablename/label- optionalexpressionformatstring- optionalwidth- optionalalignment- optional
Format-Wideexpressionformatstring- optional
Group-Objectexpression
Measure-Object- Only supports a script block for the expression, not a hashtable.
- Not supported in PowerShell 5.1 and older.
Select-Objectname/label- optionalexpression
Sort-Objectexpressionascending/descending- optional
Note
The value of the expression can be a script block instead of a
hashtable. For more information, see the Notes section.
Hashtable key definitions
name/label- Specifies the name of the property being created. You can usenameor its alias,label, interchangeably.expression- A string or script block used to calculate the value of the new property. If theexpressionis a string, the value is interpreted as a property name on the input object. This is a shorter option thanexpression = { $_.<PropertyName> }.alignment- Used by cmdlets that produce tabular output to define how the values are displayed in a column. The value must be'left','center', or'right'.formatstring- Specifies a format string that defines how the value is formatted for output. For more information about format strings, see Format types in .NET.width- Specifies the maximum width column in a table when the value is displayed. The value must be greater than0.depth- The Depth parameter ofFormat-Customspecifies the depth of expansion for all properties. Thedepthkey allows you to specify the depth of expansion per property.ascending/descending- Allows you to specify the order of sorting for one or more properties. These are boolean values.
You don't need to spell out the hashtable keys as long as the specified name
prefix is unambiguous. For example, you can use n instead of Name and e
instead of Expression.
Examples
Compare-Object
With calculated properties, you can control how the properties of the input objects are compared. In this example, rather than comparing the values directly, the values are compared to the result of the arithmetic operation (modulus of 2).
Compare-Object @{p=1} @{p=2} -property @{ Expression = { $_.p % 2 } }
$_.p % 2 SideIndicator
---------- -------------
0 =>
1 <=
ConvertTo-Html
ConvertTo-Html can convert a collection of objects to an HTML table.
Calculated properties allow you to control how the table is presented.
Get-Alias |
ConvertTo-Html Name,
Definition,
@{
name='ParameterCount'
expr={$_.Parameters.Keys.Count}
align='center'
} |
Out-File .\aliases.htm -Force
This example creates an HTML table containing a list of PowerShell aliases and the number parameters for each aliased command. The values of ParameterCount column are centered.
Format-Custom
Format-Custom provides a custom view of an object in a format similar to a
class definition. More complex objects can contain members that are deeply
nested with complex types. The Depth parameter of Format-Custom specifies
the depth of expansion for all properties. The depth key allows you to
specify the depth of expansion per property.
In this example, the depth key simplifies the custom output for the
Get-Date cmdlet. Get-Date returns a DateTime object. The Date
property of this object is also a DateTime object, so the object is nested.
Get-Date | Format-Custom @{expr={$_.Date};depth=1},TimeOfDay
class DateTime
{
$_.Date =
class DateTime
{
Date = 8/7/2020 12:00:00 AM
Day = 7
DayOfWeek = Friday
DayOfYear = 220
Hour = 0
Kind = Local
Millisecond = 0
Minute = 0
Month = 8
Second = 0
Ticks = 637323552000000000
TimeOfDay = 00:00:00
Year = 2020
DateTime = Friday, August 07, 2020 12:00:00 AM
}
TimeOfDay =
class TimeSpan
{
Ticks = 435031592302
Days = 0
Hours = 12
Milliseconds = 159
Minutes = 5
Seconds = 3
TotalDays = 0.503508787386574
TotalHours = 12.0842108972778
TotalMilliseconds = 43503159.2302
TotalMinutes = 725.052653836667
TotalSeconds = 43503.1592302
}
}
Format-List
In this example, we use calculated properties to change the name and format of
the output from Get-ChildItem.
Get-ChildItem *.json -File |
Format-List Fullname,
@{
name='Modified'
expression={$_.LastWriteTime}
formatstring='O'
},
@{
name='Size'
expression={$_.Length/1KB}
formatstring='N2'
}
FullName : C:\Git\PS-Docs\PowerShell-Docs\.markdownlint.json
Modified : 2020-07-23T10:26:28.4092457-07:00
Size : 2.40
FullName : C:\Git\PS-Docs\PowerShell-Docs\.openpublishing.publish.config.json
Modified : 2020-07-23T10:26:28.4092457-07:00
Size : 2.25
FullName : C:\Git\PS-Docs\PowerShell-Docs\.openpublishing.redirection.json
Modified : 2020-07-27T13:05:24.3887629-07:00
Size : 324.60
Format-Table
In this example, the calculated property adds a Type property used to classify the files by the content type.
Get-ChildItem -File |
Sort-Object extension |
Format-Table Name, Length -GroupBy @{
name='Type'
expression={
switch ($_.extension) {
'.md' {'Content'}
'' {'Metacontent'}
'.ps1' {'Automation'}
'.yml' {'Automation'}
default {'Configuration'}
}
}
}
Type: Metacontent
Name Length
---- ------
ThirdPartyNotices 1229
LICENSE-CODE 1106
LICENSE 19047
Type: Configuration
Name Length
---- ------
.editorconfig 183
.gitattributes 419
.gitignore 228
.markdownlint.json 2456
.openpublishing.publish.config.json 2306
.openpublishing.redirection.json 332394
.localization-config 232
Type: Content
Name Length
---- ------
README.md 3355
CONTRIBUTING.md 247
Type: Automation
Name Length
---- ------
.openpublishing.build.ps1 796
build.ps1 7495
ci.yml 645
ci-steps.yml 2035
daily.yml 1271
Format-Wide
The Format-Wide cmdlet allows you to display the value of one property for
objects in a collection as a multi-column list.
For this example, we want to see the filename and the size (in kilobytes) as a
wide listing. Since Format-Wide doesn't display more than one property, we
use a calculated property to combine the value of two properties into a single
value.
Get-ChildItem -File |
Format-Wide -Property @{e={'{0} ({1:N2}kb)' -f $_.name,($_.length/1kb)}}
.editorconfig (0.18kb) .gitattributes (0.41kb)
.gitignore (0.22kb) .localization-config (0.23kb)
.markdownlint.json (2.40kb) .openpublishing.build.ps1 (0.78kb)
.openpublishing.publish.config.json (2.25kb) .openpublishing.redirection.json (324.60kb)
build.ps1 (7.32kb) ci.yml (0.63kb)
ci-steps.yml (1.99kb) CONTRIBUTING.md (0.24kb)
daily.yml (1.24kb) LICENSE (18.60kb)
LICENSE-CODE (1.08kb) README.md (3.28kb)
ThirdPartyNotices (1.20kb)
Group-Object
The Group-Object cmdlet displays objects in groups based on the value of a
specified property. In this example, the calculated property counts the number
of files of each content type.
Get-ChildItem -File |
Sort-Object extension |
Group-Object -NoElement -Property @{
expression={
switch ($_.extension) {
'.md' {'Content'}
'' {'Metacontent'}
'.ps1' {'Automation'}
'.yml' {'Automation'}
default {'Configuration'}
}
}
}
Count Name
----- ----
5 Automation
7 Configuration
2 Content
3 Metacontent
Measure-Object
The Measure-Object cmdlet calculates the numeric properties of objects. In
this example, we use a calculated property to get the count of the numbers
between 1 and 10 that are evenly divisible by 3.
The script block returns $true if the number is divisible by 3 and $false
for all other numbers. The Sum operation treats $true values as 1 and
$false values as 0.
1..10 | Measure-Object -Property {($_ % 3) -eq 0} -Sum
Count : 10
Average :
Sum : 3
Maximum :
Minimum :
StandardDeviation :
Property : ($_ % 3) -eq 0
Note
Unlike the other cmdlets, Measure-Object doesn't accept a hashtable for
calculated properties. You must use a script block.
Select-Object
You can use calculated properties to add additional members to the objects
output with the Select-Object cmdlet. In this example, we're listing the
PowerShell aliases that begin with the letter C. Using Select-Object, we
output the alias, the cmdlet it's mapped to, and a count for the number of
parameters defined for the cmdlet. Using a calculated property, we can create
the ParameterCount property.
$aliases = Get-Alias c* |
Select-Object Name,
Definition,
@{
name='ParameterCount'
expr={$_.Parameters.Keys.Count}
}
$aliases | Get-Member
$aliases
TypeName: Selected.System.Management.Automation.AliasInfo
Name MemberType Definition
---- ---------- ----------
Equals Method bool Equals(System.Object obj)
GetHashCode Method int GetHashCode()
GetType Method type GetType()
ToString Method string ToString()
Definition NoteProperty string Definition=Get-Content
Name NoteProperty string Name=cat
ParameterCount NoteProperty System.Int32 ParameterCount=21
Name Definition ParameterCount
---- ---------- --------------
cat Get-Content 21
cd Set-Location 15
cdd Push-MyLocation 1
chdir Set-Location 15
clc Clear-Content 20
clear Clear-Host 0
clhy Clear-History 17
cli Clear-Item 20
clp Clear-ItemProperty 22
cls Clear-Host 0
clv Clear-Variable 19
cnsn Connect-PSSession 29
compare Compare-Object 20
copy Copy-Item 24
cp Copy-Item 24
cpi Copy-Item 24
cpp Copy-ItemProperty 23
cvpa Convert-Path 13
Sort-Object
Using the calculated properties, you can sort data in different orders per property. This example sorts data from a CSV file in ascending order by Date. But within each date, it sorts the rows in descending order by UnitsSold.
Import-Csv C:\temp\sales-data.csv |
Sort-Object Date, @{expr={$_.UnitsSold}; desc=$true}, Salesperson |
Select-Object Date, Salesperson, UnitsSold
Date Salesperson UnitsSold
---- ----------- ---------
2020-08-01 Sally 3
2020-08-01 Anne 2
2020-08-01 Fred 1
2020-08-02 Anne 6
2020-08-02 Fred 2
2020-08-02 Sally 0
2020-08-03 Anne 5
2020-08-03 Sally 3
2020-08-03 Fred 1
2020-08-04 Anne 2
2020-08-04 Fred 2
2020-08-04 Sally 2
Notes
You may specify the expression script block directly, as an argument, rather than specifying it as the
Expressionentry in a hashtable. For example:'1', '10', '2' | Sort-Object { [int] $_ }This example is convenient for cmdlets that don't require (or support) naming a property via the
Namekey, such asSort-Object,Group-Object, andMeasure-Object.For cmdlets that support naming the property, the script block is converted to a string and used as the name of the property in the output.
Expressionscript blocks run in child scopes, meaning that the caller's variables can't be directly modified.Pipeline logic is applied to the output from
Expressionscript blocks. This means that outputting a single-element array causes that array to be unwrapped.For most cmdlets, errors inside expression script blocks are quietly ignored. For
Sort-Object, statement-terminating and script-terminating errors are output but they don't terminate the statement.
