Given an array $arr = 1,2,3,4, I want to create a new array with a sliding window of the value. My specific need is for a window of size 2, so the result is [[1,2],[2,3],[3,4]], but would like to know if there is a generic solution.
My ultimate need is to calculate the difference between consecutive elements, to get [1,1,1,1].
Arrays are very tricky. See generic solution to sliding window and your ultimate need below:
$arr = 1,2,3,4
#create window, notice comma (,)
$result = 1..($arr.Length-1) | % { ,($arr[$_-1], $arr[$_]) }
#show elements
"[0][0]=$($result[0][0])"
"[0][1]=$($result[0][1])"
#ultimate need
1..($arr.Length-1) | % { $arr[$_]-$arr[$_-1] }
Take a look at this fragment from about_Arrays documentation:
You can also get the members of an array by typing a comma (,) before
the value that is piped to the Get-Member cmdlet. The comma makes the
array the second item in an array of arrays. Windows PowerShell pipes
the arrays one at a time and Get-Member returns the members of the
array.
,$a | Get-Member
,(1,2,3) | Get-Member
Why don't you simply calculate a new array with the differences between the consecutive elements, if that's what you're actually after?
$diff = #(for ($i=0; $i -lt $arr.Count-1; $i++) {
$arr[$i+1] - $arr[$i]
})
The resulting array would be [1,1,1], though, as the last element of $arr doesn't have a neighboring element to be compared to.
Related
In Powershell, I have a hash table that contains data similar to this -
Name Value
---- -----
1-update.bat 1
2-update.bat 2
3-update.bat 3
3.1-update.bat 3.1
4-update.bat 4
I also have an variable that contians a number, for example 3
What I would like to do is loop through the array and remove any entry where the value is less than or equal to 3
I'm thinking that this will be easy, especially as the docs say that has tables contain a .remove method. However, the code I have below fails, yeilding this error -
Exception calling "Remove" with "1" argument(s): "Collection was of a
fixed size."
Here is the code that I used -
$versions = #{}
$updateFiles | ForEach-Object {
$versions.Add($_.name, [decimal]($_.name -split '-')[0])
}
[decimal]$lastUpdate = Get-Content $directory\$updatesFile
$versions | ForEach-Object {
if ( $_.Value -le $lastUpdate ) {
$versions.Remove($version.Name)
}
}
I first tried to loop $versions in a different manner, trying both the foreach and for approaches, but both failed in the same manner.
I also tried to create a temporary array to hold the name of the versions to remove, and then looping that array to remove them, but that also failed.
Next I hit Google, and while I can find several similar questions, none that answer my specific question. Mostly they suggest using a list (New-Object System.Collections.Generic.List[System.Object]), whcih from what I can tell is of no help to me here.
Is anyone able to suggest a fix?
Here you go, you can use .Remove(), you just need a clone of the hashtable so that it will let you remove items as you enumerate.
[hashtable]$ht = #{ '1-update.bat'=1;'2-update.bat'=2;'3-update.bat'=3;'3.1-update.bat'=3.1; '4-update.bat'=4 }
#Clone so that we can remove items as we're enumerating
$ht2 = $ht.Clone()
foreach($k in $ht.GetEnumerator()){
if([decimal]$k.Value -le 3){
#notice, deleting from clone, then return clone at the end
$ht2.Remove($k.Key)
}
}
$ht2
Notice I've cast the original variable too so that it's explicitly a hash table, may not be required, but I like to do it to at least keep things clear.
It looks like you just confused ForEach-Object with foreach but only halfway (maybe it was foreach before and you converted it).
You can't send a [hashtable] directly to ForEach-Object; the $_ in that case will just refer to the single [hashtable] you sent in. You can do:
foreach ($version in $versions.GetEnumerator()) {
$version.Name
$version.Value
}
or you can do something like this:
$versions.Keys | ForEach-Object {
$_ # the name/key
$versions[$_] # the value
$versions.$_ # also the value
}
$ht.Keys # list all keys
$ht[$_] # take an element of hastable
$ht.Remove($_) # remove an element of hastable by his key
what you want:
$ht.Keys | ? { $ht[$_] -le 3 } | %{$ht.Remove($_) }
You need to create a temporary array to hold the name/key of the versions to remove, and then looping that array to remove them from hash table:
$versionKeysToRemove = $versions.Keys | Where-Object { $versions[$_] -le $lastUpdate }
$versionKeysToRemove | ForEach-Object { $versions.Remove($_) }
Or shorter:
($versions.Keys | ? { $versions[$_] -le $lastUpdate }) | % { $versions.Remove($_) }
Please note the parentheses.
Sometimes PowerShell is completely awesome and other times it is completely frustrating and unintuitive. It is almost always an array that is causing me grief.
This time I have an array of strings. I want to split each string on white space so that I end up with an array of arrays of strings. I have tried this:
$data | ForEach-Object { $_.Split(#(), [System.StringSplitOptions]::RemoveEmptyEntries) }
But that just flattens everything into one large array of strings like SelectMany in C#. I have also tried this:
$data | Select-Object { $_.Split(#(), [System.StringSplitOptions]::RemoveEmptyEntries) }
But that gives me an array of PsCustomObject. I feel like this should be incredibly easy. Am I missing something completely obvious?
You can put unary comma (array) operator to prevent PowerShell to enumerate an array, returned by Split method:
$data | ForEach-Object { ,$_.Split(#(), [System.StringSplitOptions]::RemoveEmptyEntries) }
How about this? What I do here is I loop through all of the elements in the array, and then I do the split and replace the current item with the returned String[] from the Split():
$Outer = "hello there", "how are you?", "I'm good, thanks"
for ($i = 0; $i -lt $Outer.Count; $i++) {
$Outer[$i] = $Outer[$i].Split(" ")
}
$Outer[1][2]
# you?
$Outer[2][0]
# I'm
I'm trying to export some lists from Sharepoint into a CSV file. My goal is to make a single function that is flexible enough to take a List name, identifier for the CSV file, and a list of FieldValues to export, and then produce a CSV file. Here's what I have so far:
function getTableData($_ctx, [string]$_colName)
{
$list = $_ctx.Web.Lists.GetByTitle("$_colName")
$camlQuery = [Microsoft.SharePoint.Client.CamlQuery]::CreateAllItemsQuery(100)
$colItems = $list.GetItems($camlQuery)
$_ctx.Load($colItems)
$_ctx.ExecuteQuery();
return $colItems
}
# More will go into this array, but for now a single entry is sufficient for testing purposes
$mstLists = #("GroupMst", "Groups", #("Title", "GroupCode"))
$cols = #()
foreach($col in $mstLists[0][2])
{
$cols += #{Name=$col;expression={$_[$col];}}
}
$cols
# Grab all items from a list
getListData $ctx $mstLists[0][0] |
%{ select-object -input $_ -prop $cols } |
Export-Csv -Path ($export_path + '\' + $current_date + '_' + $mstLists[0][1] + '.csv') -Encoding UTF8 -NoTypeInformation
The problem I'm having is in the loop that populates $cols. Basically, each item needs to look like #{Name="Title";expression={$_["Title"];}} in order for select-object in the ForEach to grab the proper fields from the List. Unfortunately $cols ends up being looking like this:
Name Value
---- -----
expression $_[$col];
Name Title
expression $_[$col];
Name GroupCode
Which (somehow) produces a CSV file that looks like this:
"Title","GroupCode"
"LA","LA"
"NY","NY"
"TK","TK"
When the output needs to look like this:
"Title","GroupCode"
"Los Angeles","LA"
"New York","NY"
"Tokyo","TK"
I know the field names are correct - if I hardcode them in like so...
# Grab all items from a list
getListData $ctx $mstLists[0][0] |
%{ select-object -input $_ -prop `
#{Name="Title";expression={$_["Title"];}}, `
#{Name='GroupCode';expression={$_["GroupCode"];}}; } |
Export-Csv -Path ($export_path + '\' + $current_date + '_' + $mstLists[0][1] + '.csv') -Encoding UTF8 -NoTypeInformation
...then I get the desired CSV output. I just can't figure out how to get $_[$col] to instead return $_["Title"]
Not sure what the $mstLists[0][2] meant to refer to, but the following code seems to give what you are after...
$mstLists = #("GroupMst", "Groups", #("Title", "GroupCode"))
$cols = #()
foreach($col in $mstLists[2])
{
$cols += #{Name=$col; Expression = [scriptblock]::Create('$_["{0}"]' -f $col)}
}
$cols
which gives...
Name Value
---- -----
Name Title
Expression $_["Title"]
Name GroupCode
Expression $_["GroupCode"]
In your response to andyb in the comments, you say that each item of the array will follow the format
#("ListName", "CSVFileID", #("Field1", "Field2", "Etc..."))
and that $mstLists[0][2] "refers to the list of fields in the first item in the array."
The problem is that it doesn't refer to the list of fields in the first item of the array, because the first item of the array isn't a list of anything, it's the string GroupMst. When you index into a string, you get the character indicated by the index. Since $mstLists[0] is a string, $mstLists[0][2] returns the third character of that string, which is o.
I suppose you were expecting that the # operator would make the array in the parentheses a single item, which becomes the first element of $mstLists? It doesn't. All the # does is ensure that the expression in the parentheses is evaluated as an array rather than a scalar. So, with $a = ('string'), $a is a string, whereas with $a = #('string'), $a is an array with a single string element.
However, since ("GroupMst", "Groups", #("Title", "GroupCode")) evaluates to an array anyway, putting an # in front of it is redundant. Either way you're still assigning a literal array to the variable. $mstLists is an array of three elements:
Element 0 is the string GroupMst
Element 1 is the string Groups
Element 2 is an array of the strings Title and GroupCode
What you want to do is use , as a unary operator:
$mstLists = , ("GroupMst", "Groups", #("Title", "GroupCode"))
Now $mstLists is an array of a single item whose value is the array described in the bulleted list above, and $mstLists[0][2] evaluates to an array of the strings Title and GroupCode, as you were expecting.
Note that , works as a unary or binary operator that returns an array of the operands. To return a single-element array, you use it as a unary operator in front of that element. If you have multiple literal arrays that you want to assign to mstLists, you only need commas between them, not the one in front:
$mstLists = ("ListName", "CSVFileID", #("Field1", "Field2", "Etc...")), ("ListName2", "CSVFileID2", #("Field1", "Field2", "Etc..."))
That addresses the main problem. That still won't quite give you what you want, because $col won't get interpolated in the Expression scriptblock, so Expression will always be literally $_[$col]. However, in order to figure out how to do what you actually want to do, it would be helpful to see a sample of the contents of $ctx.
This might be weird, but stay with me.
I want to get only the last element of a piped result to be assigned to a varaiable.
I know how I would do this in "regular" code of course, but since this must be a one-liner.
More specifically, I'm interested in getting the file extension when getting the result from an FTP request ListDirectoryDetails.
Since this is done within a string expansion, I can't figure out the proper code.
Currently I'm getting the last 3 hars, but that is real nasty.
New-Object PSObject -Property #{
LastWriteTime = [DateTime]::ParseExact($tempDate, "MMM dd HH:mm",[System.Globalization.CultureInfo]::InvariantCulture)
Type = $(if([int]$tempSize -eq 0) { "Directory" } else { $tempName.SubString($tempName.length-3,3) })
Name = $tempName
Size = [int]$tempSize
}
My idea was doing something similar to
$tempName.Split(".") | ? {$_ -eq $input[$input.Length-1]}
that is, iterate over all, but only take out where the element I'm looking at is the last one of the input-array.
What am I missing ?
A few ways to do this:
$name = 'c:\temp\aaa.bbb.ccc'
# way 1
$name.Split('.') | Select-Object -Last 1
# way 2
[System.IO.Path]::GetExtension($name)
# or if the dot is not needed
[System.IO.Path]::GetExtension($name).TrimStart('.')
In general, getting the last element in the pipeline would be done using Select -Last 1 as Roman suggests above. However, an alternate and easier way to do this if the input is a simple array is to use array slicing e.g.:
PS> $name = "c:\temp\aaa.bbb.txt"
PS> $name.Split('.')[-1]
txt
Was your intent to get the file's extension or basename? Because it seems that the Type property already contains the extension for the filename.
The Powershell code:
$list += "aa"
appends the element "aa" to the list $list. Is there a way to prepend an element? This is my solution, but there must be a way to do this in a single line.
$tmp = ,"aa";
$tmp += $list
$list = $tmp
In your example above, you should just be able to do:
$list = ,"aa" + $list
That will simply prepend "aa" to the list and make it the 0th element. Verify by getting $list[0].
Using += and + on arrays in PowerShell is making a copy of the array every time you use it. That is fine unless the list/array is really large. In that case, consider using a generic list:
C:\> $list = new-object 'System.Collections.Generic.List[string]'
C:\> $list.Add('a')
C:\> $list.Add('b')
C:\> $list.Insert(0,'aa')
C:\> $list
aa
a
b
Note that in this scenario you need to use the Add/Insert methods. If you fall back to using +=, it will copy the generic list back to an object[].
This combines two arrays into one.
$list = #("aa") + $list
It's impossible to do a pure prepending into a PowerShell array, because PowerShell arrays are fixed length. Combining two arrays into one is a good approach.
If you happen to want to do this to an 'Object' array rather than a 'String', I found the following useful:
$List = $List | foreach {'aa' + $_}
Obviously, this would be relatively slow for a gigantic array.