Error When Calculating Standard Deviation in PowerShell - csv

Question

I'm attempting to calculate some statistics for the values in each column of a CSV file using PowerShell. The Measure-Object cmdlet seems like it will do the trick for everything I need other than the Standard Deviation. I tracked down a description online where the Standard Deviation is calculated using [MATH], but when I run the code, I get the following error on the lines containing Pow():
Method invocation failed because system.management.automation.psobject doesn't contain a method named 'op_Subtraction'.
Here's my code, any help would be appreciated:
$i = 1
While ($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 - $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
#Append the standard deviation variable to the statistics array and add the value
$colSTDDEV = New-Object System.Data.DataColumn StdDev,([double])
$colVZA = New-Object System.Data.DataColumn VZA,([double])
$colVAZ = New-Object System.Data.DataColumn VAZ,([double])
$VZA = $Stats.VZA
$VAZ = $Stats.VAZ
$STATS.Columns.Add($colSTDDEV)
$STATS[0].StandardDev = $STDEV
$STATS.Columns.Add($colVZA)
$STATS[0].StandardDev = $VZA
$STATS.Columns.Add($colVAZ)
$STATS[0].StandardDev = $VAZ
#Export the $STATS file containing everything you need in the correct folder
Export-CSV -notype "c:\zMFM\z550Output\20dSummer\20dSum550Statistics.csv"
}
$i++
}

Answer 1

$DevMath += [math]::pow(($Y - $STDEVAVG.Average), 2)
You may have to replace this with:
$DevMath += [math]::pow(($Y.Average - $STDEVAVG.Average), 2)
since $Y seems to be an object, not a numeric value.