Newly Created Column is Null.... Why? - csv

Question

I'm trying to do a simple task in PowerShell where some basic statistics are calculated for a number of columns in a CSV file. I'm nearly done, but I keep getting an error where new columns I create are coming up as being Null. I cannot see where I am going wrong, here.
Specifically, the line of code causing the error is
$STATS2.Columns.Add($colVZA) |
The tables created when importing $filename do have columns named VZA, VAZ, etc., so that's not the problem.
It seems like adding and populating columns should be a simple task, so I'm sure I'm missing something simple here. Here's my code:
#######################
function Get-Type
{
param($type)
$types = #(
'System.Boolean',
'System.Byte[]',
'System.Byte',
'System.Char',
'System.Datetime',
'System.Decimal',
'System.Double',
'System.Guid',
'System.Int16',
'System.Int32',
'System.Int64',
'System.Single',
'System.UInt16',
'System.UInt32',
'System.UInt64')
if ( $types -contains $type ) {
Write-Output "$type"
}
else {
Write-Output 'System.String'
}
} #Get-Type
#######################
<#
.SYNOPSIS
Creates a DataTable for an object
.DESCRIPTION
Creates a DataTable based on an objects properties.
.INPUTS
Object
Any object can be piped to Out-DataTable
.OUTPUTS
System.Data.DataTable
.EXAMPLE
$dt = Get-psdrive| Out-DataTable
This example creates a DataTable from the properties of Get-psdrive and assigns output to $dt variable
.NOTES
Adapted from script by Marc van Orsouw see link
Version History
v1.0 - Chad Miller - Initial Release
v1.1 - Chad Miller - Fixed Issue with Properties
v1.2 - Chad Miller - Added setting column datatype by property as suggested by emp0
v1.3 - Chad Miller - Corrected issue with setting datatype on empty properties
v1.4 - Chad Miller - Corrected issue with DBNull
v1.5 - Chad Miller - Updated example
v1.6 - Chad Miller - Added column datatype logic with default to string
v1.7 - Chad Miller - Fixed issue with IsArray
.LINK
http://thepowershellguy.com/blogs/posh/archive/2007/01/21/powershell-gui-scripblock-monitor-script.aspx
#>
function Out-DataTable
{
[CmdletBinding()]
param([Parameter(Position=0, Mandatory=$true, ValueFromPipeline = $true)] [PSObject[]]$InputObject)
Begin
{
$dt = new-object Data.datatable
$First = $true
}
Process
{
foreach ($object in $InputObject)
{
$DR = $DT.NewRow()
foreach($property in $object.PsObject.get_properties())
{
if ($first)
{
$Col = new-object Data.DataColumn
$Col.ColumnName = $property.Name.ToString()
if ($property.value)
{
if ($property.value -isnot [System.DBNull]) {
$Col.DataType = [System.Type]::GetType("$(Get-Type $property.TypeNameOfValue)")
}
}
$DT.Columns.Add($Col)
}
if ($property.Gettype().IsArray) {
$DR.Item($property.Name) =$property.value | ConvertTo-XML -AS String -NoTypeInformation -Depth 1
}
else {
$DR.Item($property.Name) = $property.value
}
}
$DT.Rows.Add($DR)
$First = $false
}
}
End
{
Write-Output #(,($dt))
}
$i = 1
While ($i -le 211) {
#Set the variable to the filename with the iteration number
$filename = "c:\zMFM\z550Output\20dSummer\fixed20dSum550Output$i.csv"
#Check to see if that a file with $filename exists. If not, skip to the next iteration of $i. If so, run the code to collect the statistics for each variable and output them each to a different file
If (Test-Path $filename) {
#Calculate the Standard Deviation
#First get the average of the values in the column
$STDEVInputFile = Import-CSV $filename
#Find the average and count for column 'td'
$STDEVAVG = $STDEVInputFile | Measure-Object td -Average | Select Count, Average
$DevMath = 0
# Sum the squares of the differences between the mean and each value in the array
Foreach ($Y in $STDEVInputFile) {
$DevMath += [math]::pow(($Y.Average - $STDEVAVG.Average), 2)
#Divide by the number of samples minus one
$STDEV = [Math]::sqrt($DevMath / ($STDEVAVG.Count-1))
}
#Calculate the basic statistics for column 'td' with the MEASURE-OBJECT cmdlet
$STATS = Import-CSV $Filename |
Measure-Object td -ave -max -min |
#Export the statistics as a CSV
Export-CSV -notype "c:\zMFM\z550Output\20dSummer\tempstats$i.csv"
$GetColumns = Import-CSV $filename
#Append the standard deviation variable to the statistics table and add the value
$STATS2 = Import-CSV "c:\zMFM\z550Output\20dSummer\tempstats$i.csv"
$StatsTable = Get-PSDrive | Out-DataTable
#$colSTDDEV = New-Object System.Data.DataColumn StdDev,([double])
$colVZA = New-Object System.Data.DataColumn VZA,([double])
#$colVAZ = New-Object System.Data.DataColumn VAZ,([double])
$colVZA = $GetColumns[0].VZA
#$colVAZ = $GetColumns[0].VAZ #COMMENTED FOR DEBUGGING
#$colSTDDEV = $STDEV
#$StatsTable.Columns.Add($colSTDDEV) #COMMENTED FOR DEBUGGING
#$StatsTable[0].StdDev = $STDEV #COMMENTED FOR DEBUGGING
$StatsTable.Columns.Add($colVZA) |
#$StatsTable[0].VZA = $VZA
#$StatsTable.Columns.Add($colVAZ) #COMMENTED FOR DEBUGGING
#$StatsTable[0].VZA = $VAZ #COMMENTED FOR DEBUGGING
#Export the $STATS file containing everything you need in the correct folder
Export-CSV -notype "c:\zMFM\z550Output\20dSummer\20dSum550Statistics.csv"
}
$i++
}

Answer 1

Even though each object in $STATS2 have the same properties, the $STATS2 object itself is just a simple array, an unstructured list of objects - it doesn't have a Columns property with an Add() method:
$STATS2.Colums.Add($colVZA)
^ ^ ^
[array] | |
$null |
this fails
You can convert the array you get from Import-Csv from an array to a DataTable object (which has Columns) by inspecting each property in the first object in the array, like in the Out-DataTable sample on the technet script gallery