Delete Deployments from a ResourceGroup Based on a Max Number

remove-deployments.ps1

#
#this script will delete deployments from a resourceGroup if the number of deployments exceeds the number specified by the Max parameter
#
Param(
    [string] [Parameter(Mandatory=$true)] $ResourceGroupName,
    [int] [Parameter(Mandatory=$true)] $Max
)

$deployments = Get-AzureRmResourceGroupDeployment -ResourceGroupName $ResourceGroupName

if($deployments.Count -gt $Max){
    
    $numToDelete = $deployments.Count - $Max

    $i = 1
    while($i -le $numToDelete){
        write-host "Deleting Deployment: "$deployments[$deployments.Count - $i].DeploymentName
        Remove-AzureRmResourceGroupDeployment -ResourceGroupName $ResourceGroupName -Name $deployments[$deployments.Count - $i].DeploymentName -Verbose
        $i++
    }

}

Good catch - see this one for an approach that uses jobs.