Count columns of an imported Excel workbook - count a given object's properties

tl;dr:

@($columns.psobject.properties).Count

What you're looking for is the count of an object's properties, which can be done via the .psobject.properties collection, which is available on any object in PowerShell - and therefore also on the [pscustomobject] instances returned by Import-Excel - as a reflection feature that allows you to inspect a given object's properties.

Counting the properties is tricky, because the specific collection data type returned by .psobject.properties - [System.Management.Automation.PSMemberInfoIntegratingCollection[System.Management.Automation.PSPropertyInfo]] - unexpectedly implements neither a .Count nor a .Length property.

The workaround is to use @(...), the array subexpression operator, to collect the individual properties as a regular PowerShell array ([object[]]), on which you can then call .Count:

@($columns.psobject.properties).Count

See this GitHub issue, which asks for a .Count property to be implemented on the collection returned by .psobject.properties so as to render this workaround unnecessary.

This seems to have done it.

$columns = (($columns[0].psobject.properties).Count).Count