6.3 Measure Statistical Properties of a List

Problem

You want to measure the numeric (minimum, maximum, sum, average) or textual (characters, words, lines) features of a list of objects.

Solution

Use the Measure-Object cmdlet to measure these statistical properties of a list.

To measure the numeric features of a stream of objects, pipe those objects to the Measure-Object cmdlet:

PS > 1..10 | Measure-Object -Average -Sum

Count             : 10
Average           : 5.5
Sum               : 55
Maximum           :
Minimum           :
StandardDeviation :
Property          :

To measure the numeric features of a specific property in a stream of objects, supply that property name to the -Property parameter of the Measure-Object cmdlet. For example, in a directory with files:

PS > Get-ChildItem |
    Measure-Object -Property Length -Max -Min -Average -Sum -StandardDeviation

Count             : 57
Average           : 29769.0526315789
Sum               : 1696836
Maximum           : 135519
Minimum           : 26
StandardDeviation : 30753.5324436891
Property          : Length

To measure the textual features of a stream of objects, use the -Character, -Word, and -Line parameters of the Measure-Object cmdlet:

PS > Get-ChildItem > output.txt
PS > Get-Content output.txt | Measure-Object -Character -Word -Line

            Lines             Words       Characters Property
            -----             -----       ---------- --------
              964              6083            33484

Discussion

By default, the Measure-Object cmdlet counts only the number of objects it receives. If you want to measure additional properties (such as the maximum, minimum, average, sum, characters, words, or lines) of those objects, then you need to specify them as options to the cmdlet.

For the numeric properties, though, you usually don’t want to measure the objects themselves. Instead, you probably want to measure a specific property from the list—such as the Length property of a file. For that purpose, the Measure-Object cmdlet supports the -Property parameter to which you provide the property you want to measure.

Sometimes you might want to measure a property that isn’t a simple number—such as the LastWriteTime property of a file. Since the LastWriteTime property is a DateTime, you can’t determine its average immediately. However, if any property allows you to convert it to a number and back in a meaningful way (such as the Ticks property of a DateTime), then you can still compute its statistical properties. Example 6-2 shows how to get the average LastWriteTime from a list of files.

PS > ## Get the LastWriteTime from each file
PS > $times = dir | ForEach-Object { $_.LastWriteTime }

PS > ## Measure the average Ticks property of those LastWriteTime
PS > $results = $times | Measure-Object Ticks -Average

PS > ## Create a new DateTime out of the average Ticks
PS > New-Object DateTime $results.Average

Sunday, June 11, 2006 6:45:01 AM

For more information about the Measure-Object cmdlet, type Get-Help Measure-Object.