What's the proper way to iteratively grab a value from an array when the key is a string? - powershell

Question

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"]

Answer 1

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"]

Answer 2

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.