count xml child nodes

Mike Bates

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Apr 6, 2010, 5:44:08 AM4/6/10

to

As a newbie to PS I'm very impressed as to what it can do, but I'm
having trouble understanding some of the subtleties. I'm trying to
process a large XML file, roughly of the form shown in the code
snippet below, but have hit an issue I don't understand. The code that
explains this is...

$xW = [xml]@'
<W>
<X xID="1">
<Y yID="20">
<Z zID="201"/>
</Y>
<Y yID="30">
<Z zID="301"/>
<Z zID="302"/>
</Y>
</X>
</W>
'@
write-host First Y Node Z count = $xW.W.X.Y[0].Z.Count
write-host Second Y Node Z count = $xW.W.X.Y[1].Z.Count

The output from this is:

First Y Node Z count =
Second Y Node Z count = 2

I was expecting the first output line to indicate a count of 1.

What I'm trying to achieve is to output a csv file of the form
xID,yID,zID where zID is a null value if there are no Z child nodes,
or there are multiple xID,yID lines when more than one Z child node
exists in a Y node.

HC

Chris Dent

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Apr 6, 2010, 6:08:39 AM4/6/10

to

The first of those is a single value, it has no Count property because
it's type is XmlElement not Object[] (in the case of 1, an object array
where each member is XmlElement).

See:

$xW.W.X.Y[0].Z.GetType()
$xW.W.X.Y[1].Z.GetType()
$xW.W.X.Y[1].Z | %{ $_.GetType() }

You can force it to be an array (remember to do it for index 1 if you
don't know how many children it has first):

write-host First Y Node Z count = ([Array]($xW.W.X.Y[0].Z)).Count
write-host Second Y Node Z count = ([Array]($xW.W.X.Y[1].Z)).Count

Or you can use Measure-Object:

write-host First Y Node Z count = ($xW.W.X.Y[0].Z | Measure-Object).Count
write-host Second Y Node Z count = ($xW.W.X.Y[1].Z | Measure-Object).Count

HTH

Chris

Clint B

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Apr 6, 2010, 11:50:52 AM4/6/10

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Using a little XPATH you can avoid the whole "is it an array" issue (and
scale to more nodes a little easier):

$xw.SelectNodes("/W/X/Y") | % { $_.createnavigator().evaluate("count(./Z)")}

1
2

And if you want the output labeled:
$xw.SelectNodes("/W/X/Y") | % { $i = 1 } { $count =
$_.createnavigator().evaluate("count(./Z)") ; "Y Node Z Count #{0} :
{1}" -f $i++,$count }

For some good reads on XML/XPATH & PowerShell:
http://www.pluralsight.com/community/blogs/dan/archive/2006/11/25/42506.aspx
http://www.pluralsight.com/community/blogs/dan/archive/2006/11/28/43561.aspx
http://powershell.com/cs/blogs/tobias/archive/2009/01/17/xml-part-1-playing-with-rss-feeds-and-xml-content.aspx
http://powershell.com/cs/blogs/tobias/archive/2009/02/02/xml-part-2-write-add-and-change-xml-data.aspx

HTH :)

--
v(^_^)~Clint
http://outputredirection.blogspot.com

Larry__Weiss

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Apr 6, 2010, 1:51:22 PM4/6/10

to

On 4/6/2010 10:50 AM, Clint B wrote:
> For some good reads on XML/XPATH & PowerShell:
> http://www.pluralsight.com/community/blogs/dan/archive/2006/11/25/42506.aspx
> http://www.pluralsight.com/community/blogs/dan/archive/2006/11/28/43561.aspx
> http://powershell.com/cs/blogs/tobias/archive/2009/01/17/xml-part-1-playing-with-rss-feeds-and-xml-content.aspx
> http://powershell.com/cs/blogs/tobias/archive/2009/02/02/xml-part-2-write-add-and-change-xml-data.aspx
>

The best thing I love about PowerShell is that it is such a great way to get
experience with concepts like XML/XPATH.

- Larry

stej

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Apr 7, 2010, 2:08:16 AM4/7/10

to

Good suggestions guys!
Note as well that there are living .NET objects in the background, so
you can use

PS> $xW.w.x.Y[0].haschildnodes
True
PS> $xW.w.x.Y[0].childnodes.count
1