PowerShell array initialization

Question

What s the best way to initialize an array in PowerShell   For example  the code   array       for  i 0   i -lt 5  i           array  i     FALSE     generates the error  Array assignment failed because index  0  was out of range  At H  Software PowerShell TestArray ps1 4 char 10            array    lt  lt  lt  lt  i     FALSE

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Here s two more ways  both very concise    arr1     0    20  arr2    0   20

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The solution I found was to use the New-Object cmdlet to initialize an array of the proper size    array   new-object object   5  for  i 0   i -lt  array Length  i           array  i     FALSE

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Here s another idea  You have to remember  that it s  NET underneath    arr    System Array   CreateInstance  System Object   5   arr GetType    arr Length   arr    Object     new 5   arr GetType    arr Length   Result   IsPublic IsSerial Name                                     BaseType                                                                                                -------- -------- ----                                     --------                                                                                                True     True     Object                                   System Array                                                                                            5 True     True     Object                                   System Array                                                                                            5   Using new   has one distinct advantage  when you re programming in ISE and want to create an object  ISE will give you hint with all paramer combinations and their types  You don t have that with New-Object  where you have to remember the types and order of arguments

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You can also rely on the default value of the constructor if you wish to create a typed array    gt   a   new-object bool   5  gt   a False False False False False   The default value of a bool is apparently false so this works in your case  Likewise if you create a typed int   array  you ll get the default value of 0   Another cool way that I use to initialze arrays is with the following shorthand    gt   a     false   false   false   false   false   gt   a False False False False False   Or if you can you want to initialize a range  I ve sometimes found this useful       a    1  5        a 1 2 3 4 5   Hope this was somewhat helpful

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If I don t know the size up front  I use an arraylist instead of an array    al   New-Object System Collections ArrayList for  i 0   i -lt 5   i           al Add  i

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The original example returns an error because the array is created empty  then you try to access the nth element to assign it a value    The are a number of creative answers here  many I didn t know before reading this post  All are fine for a small array  but as n0rd points out  there are significant differences in performance    Here I use Measure-Command to find out how long each initialization takes  As you might guess  any approach that uses an explicit PowerShell loop is slower than those that use  Net constructors or PowerShell operators  which would be compiled in IL or native code    Summary   New-Object and   somevalue  n are fast  around 20k ticks for 100k elements     Creating an array with the range operator n  m is 10x slower  200k ticks     Using an ArrayList with the Add   method is 1000x slower than the baseline  20M ticks   as is looping through an already-sized array using for   or ForEach-Object  a k a  foreach       Appending with    is the worst  2M ticks for just 1000 elements      Overall  I d say array n is  best  because     It s fast  You can use any value  not just the default for the type  You can create repeating values  to illustrate  type this at the powershell prompt   1  10  10 -join     or   one  2 3  3  Terse syntax     The only drawback     Non-obvious   If you haven t seen this construct before  it s not apparent what it does     But keep in mind that for many cases where you would want to initialize the array elements to some value  then a strongly-typed array is exactly what you need   If you re initializing everything to  false  then is the array ever going to hold anything other than  false or  true   If not  then New-Object type   n is the  best  approach     Testing  Create and size a default array  then assign values    PS gt  Measure-Command -Expression   a   new-object object   100000    Format-List -Property  Ticks  Ticks   20039  PS gt  Measure-Command -Expression  for  i 0   i -lt  a Length  i      a  i     false     Format-List -Property  Ticks  Ticks   28866028   Creating an array of Boolean is bit little slower than and array of Object    PS gt  Measure-Command -Expression   a   New-Object bool   100000    Format-List -Property  Ticks  Ticks   130968   It s not obvious what this does  the documentation for New-Object just says that the second parameter is an argument list which is passed to the  Net object constructor   In the case of arrays  the parameter evidently is the desired size     Appending with     PS gt   a     PS gt  Measure-Command -Expression   for   i 0   i -lt 100000   i      a   false      Format-List -Property  Ticks    I got tired of waiting for that to complete  so ctrl c then    PS gt   a     PS gt  Measure-Command -Expression   for   i 0   i -lt    100   i      a   false      Format-List -Property  Ticks  Ticks   147663 PS gt   a     PS gt  Measure-Command -Expression   for   i 0   i -lt   1000   i      a   false      Format-List -Property  Ticks  Ticks   2194398   Just as  6   3  is conceptually similar to  6   6   6   so   somearray   3  ought to give the same result as   somearray    somearray    somearray    But with arrays    is concatenation rather than addition    If  array   element is slow  you might expect  array  n to also be slow  but it s not    PS gt  Measure-Command -Expression    a      false    100000     Format-List -Property  Ticks  Ticks   20131   Just like Java has a StringBuilder class to avoid creating multiple objects when appending  so it seems PowerShell has an ArrayList     PS gt   al   New-Object System Collections ArrayList PS gt  Measure-Command -Expression   for  i 0   i -lt 1000   i      al Add  false       Format-List -Property  Ticks  Ticks   447133 PS gt   al   New-Object System Collections ArrayList PS gt  Measure-Command -Expression   for  i 0   i -lt 10000   i      al Add  false       Format-List -Property  Ticks  Ticks   2097498 PS gt   al   New-Object System Collections ArrayList PS gt  Measure-Command -Expression   for  i 0   i -lt 100000   i      al Add  false       Format-List -Property  Ticks  Ticks   19866894   Range operator  and Where-Object loop    PS gt  Measure-Command -Expression    a   1  100000     Format-List -Property  Ticks  Ticks   239863 Measure-Command -Expression    a       false      Format-List -Property  Ticks  Ticks   102298091   Notes    I nulled the variable between each run   a  null   Testing was on a tablet with Atom processor  you would probably see faster speeds on other machines   edit  About twice as fast on a desktop machine   There was a fair bit of variation when I tried multiple runs  Look for the orders of magnitude rather than exact numbers   Testing was with PowerShell 3 0 in Windows 8     Acknowledgements  Thanks to  halr9000 for array n   Scott Saad and Lee Desmond for New-Object  and  EBGreen for ArrayList   Thanks to  n0rd for getting me to think about performance

User · Answer

Yet another alternative   for   i   0   i -lt 5   i           arr       false       This one works if  arr isn t defined yet   NOTE - there are better  and more performant  ways to do this    see https   stackoverflow com a 234060 4570 below as an example

User · Answer

If I don t know the size up front  I use an arraylist instead of an array    al   New-Object System Collections ArrayList for  i 0   i -lt 5   i           al Add  i

User · Answer

You can also rely on the default value of the constructor if you wish to create a typed array    gt   a   new-object bool   5  gt   a False False False False False   The default value of a bool is apparently false so this works in your case  Likewise if you create a typed int   array  you ll get the default value of 0   Another cool way that I use to initialze arrays is with the following shorthand    gt   a     false   false   false   false   false   gt   a False False False False False   Or if you can you want to initialize a range  I ve sometimes found this useful       a    1  5        a 1 2 3 4 5   Hope this was somewhat helpful

User · Answer

You can also rely on the default value of the constructor if you wish to create a typed array    gt   a   new-object bool   5  gt   a False False False False False   The default value of a bool is apparently false so this works in your case  Likewise if you create a typed int   array  you ll get the default value of 0   Another cool way that I use to initialze arrays is with the following shorthand    gt   a     false   false   false   false   false   gt   a False False False False False   Or if you can you want to initialize a range  I ve sometimes found this useful       a    1  5        a 1 2 3 4 5   Hope this was somewhat helpful

User · Answer

array       for  i 0   i -lt 5   i           array     i

User · Answer

array       for  i 0   i -lt 5   i           array     i

User · Answer

Yet another alternative   for   i   0   i -lt 5   i           arr       false       This one works if  arr isn t defined yet   NOTE - there are better  and more performant  ways to do this    see https   stackoverflow com a 234060 4570 below as an example

User · Answer

array   1  5   foreach    false

User · Answer

Yet another alternative   for   i   0   i -lt 5   i           arr       false       This one works if  arr isn t defined yet   NOTE - there are better  and more performant  ways to do this    see https   stackoverflow com a 234060 4570 below as an example

User · Answer

If I don t know the size up front  I use an arraylist instead of an array    al   New-Object System Collections ArrayList for  i 0   i -lt 5   i           al Add  i

User · Answer

Here s another typical way    array   for  i   0   i -le 4   i       false

User · Answer

If I don t know the size up front  I use an arraylist instead of an array    al   New-Object System Collections ArrayList for  i 0   i -lt 5   i           al Add  i

User · Answer

Yet another alternative   for   i   0   i -lt 5   i           arr       false       This one works if  arr isn t defined yet   NOTE - there are better  and more performant  ways to do this    see https   stackoverflow com a 234060 4570 below as an example

User · Answer

Or try this an idea  Works with powershell 5 0     bool    tf     False  5

User · Answer

array   1  5   foreach    false

User · Answer

Here s another typical way    array   for  i   0   i -le 4   i       false

User · Answer

Here s another idea  You have to remember  that it s  NET underneath    arr    System Array   CreateInstance  System Object   5   arr GetType    arr Length   arr    Object     new 5   arr GetType    arr Length   Result   IsPublic IsSerial Name                                     BaseType                                                                                                -------- -------- ----                                     --------                                                                                                True     True     Object                                   System Array                                                                                            5 True     True     Object                                   System Array                                                                                            5   Using new   has one distinct advantage  when you re programming in ISE and want to create an object  ISE will give you hint with all paramer combinations and their types  You don t have that with New-Object  where you have to remember the types and order of arguments

User · Answer

array       for  i 0   i -lt 5   i           array     i

User · Answer

Here s two more ways  both very concise    arr1     0    20  arr2    0   20

User · Answer

The solution I found was to use the New-Object cmdlet to initialize an array of the proper size    array   new-object object   5  for  i 0   i -lt  array Length  i           array  i     FALSE

User · Answer

The solution I found was to use the New-Object cmdlet to initialize an array of the proper size    array   new-object object   5  for  i 0   i -lt  array Length  i           array  i     FALSE

User · Answer

Here s two more ways  both very concise    arr1     0    20  arr2    0   20

User · Answer

array   1  5   foreach    false

User · Answer

Or try this an idea  Works with powershell 5 0     bool    tf     False  5

User · Answer

array   1  5   foreach    false

User · Answer

Here s two more ways  both very concise    arr1     0    20  arr2    0   20

User · Answer

The solution I found was to use the New-Object cmdlet to initialize an array of the proper size    array   new-object object   5  for  i 0   i -lt  array Length  i           array  i     FALSE

User · Answer

The original example returns an error because the array is created empty  then you try to access the nth element to assign it a value    The are a number of creative answers here  many I didn t know before reading this post  All are fine for a small array  but as n0rd points out  there are significant differences in performance    Here I use Measure-Command to find out how long each initialization takes  As you might guess  any approach that uses an explicit PowerShell loop is slower than those that use  Net constructors or PowerShell operators  which would be compiled in IL or native code    Summary   New-Object and   somevalue  n are fast  around 20k ticks for 100k elements     Creating an array with the range operator n  m is 10x slower  200k ticks     Using an ArrayList with the Add   method is 1000x slower than the baseline  20M ticks   as is looping through an already-sized array using for   or ForEach-Object  a k a  foreach       Appending with    is the worst  2M ticks for just 1000 elements      Overall  I d say array n is  best  because     It s fast  You can use any value  not just the default for the type  You can create repeating values  to illustrate  type this at the powershell prompt   1  10  10 -join     or   one  2 3  3  Terse syntax     The only drawback     Non-obvious   If you haven t seen this construct before  it s not apparent what it does     But keep in mind that for many cases where you would want to initialize the array elements to some value  then a strongly-typed array is exactly what you need   If you re initializing everything to  false  then is the array ever going to hold anything other than  false or  true   If not  then New-Object type   n is the  best  approach     Testing  Create and size a default array  then assign values    PS gt  Measure-Command -Expression   a   new-object object   100000    Format-List -Property  Ticks  Ticks   20039  PS gt  Measure-Command -Expression  for  i 0   i -lt  a Length  i      a  i     false     Format-List -Property  Ticks  Ticks   28866028   Creating an array of Boolean is bit little slower than and array of Object    PS gt  Measure-Command -Expression   a   New-Object bool   100000    Format-List -Property  Ticks  Ticks   130968   It s not obvious what this does  the documentation for New-Object just says that the second parameter is an argument list which is passed to the  Net object constructor   In the case of arrays  the parameter evidently is the desired size     Appending with     PS gt   a     PS gt  Measure-Command -Expression   for   i 0   i -lt 100000   i      a   false      Format-List -Property  Ticks    I got tired of waiting for that to complete  so ctrl c then    PS gt   a     PS gt  Measure-Command -Expression   for   i 0   i -lt    100   i      a   false      Format-List -Property  Ticks  Ticks   147663 PS gt   a     PS gt  Measure-Command -Expression   for   i 0   i -lt   1000   i      a   false      Format-List -Property  Ticks  Ticks   2194398   Just as  6   3  is conceptually similar to  6   6   6   so   somearray   3  ought to give the same result as   somearray    somearray    somearray    But with arrays    is concatenation rather than addition    If  array   element is slow  you might expect  array  n to also be slow  but it s not    PS gt  Measure-Command -Expression    a      false    100000     Format-List -Property  Ticks  Ticks   20131   Just like Java has a StringBuilder class to avoid creating multiple objects when appending  so it seems PowerShell has an ArrayList     PS gt   al   New-Object System Collections ArrayList PS gt  Measure-Command -Expression   for  i 0   i -lt 1000   i      al Add  false       Format-List -Property  Ticks  Ticks   447133 PS gt   al   New-Object System Collections ArrayList PS gt  Measure-Command -Expression   for  i 0   i -lt 10000   i      al Add  false       Format-List -Property  Ticks  Ticks   2097498 PS gt   al   New-Object System Collections ArrayList PS gt  Measure-Command -Expression   for  i 0   i -lt 100000   i      al Add  false       Format-List -Property  Ticks  Ticks   19866894   Range operator  and Where-Object loop    PS gt  Measure-Command -Expression    a   1  100000     Format-List -Property  Ticks  Ticks   239863 Measure-Command -Expression    a       false      Format-List -Property  Ticks  Ticks   102298091   Notes    I nulled the variable between each run   a  null   Testing was on a tablet with Atom processor  you would probably see faster speeds on other machines   edit  About twice as fast on a desktop machine   There was a fair bit of variation when I tried multiple runs  Look for the orders of magnitude rather than exact numbers   Testing was with PowerShell 3 0 in Windows 8     Acknowledgements  Thanks to  halr9000 for array n   Scott Saad and Lee Desmond for New-Object  and  EBGreen for ArrayList   Thanks to  n0rd for getting me to think about performance

User · Answer

array       for  i 0   i -lt 5   i           array     i

User · Answer

You can also rely on the default value of the constructor if you wish to create a typed array    gt   a   new-object bool   5  gt   a False False False False False   The default value of a bool is apparently false so this works in your case  Likewise if you create a typed int   array  you ll get the default value of 0   Another cool way that I use to initialze arrays is with the following shorthand    gt   a     false   false   false   false   false   gt   a False False False False False   Or if you can you want to initialize a range  I ve sometimes found this useful       a    1  5        a 1 2 3 4 5   Hope this was somewhat helpful

[arrays] PowerShell array initialization

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