PHP - How to get number of all members in a customer group

Question

I am working on a custom magento extension.

I've made a selection menu with all customer groups, here is the code of it:

$CustomerGroups = Mage::getResourceModel('customer/group_collection')->toOptionArray();

$CustomerGroups = array_merge(array('' => ''), $CustomerGroups);

$fieldset->addField('customergroups', 'select',
        array(
            'name'      => 'customergroups',
            'label'     => Mage::helper('smsnotification')->__('User Group'),
            'class'     => 'required-entry',
            'values'    => $CustomerGroups
        )
    );

Here is the result:

As you can see the results are like this:

• not logged in
• General
• Wholesale
• Retailer

What i want is simply to add the number of members in every customer group, for example General - (125 members).

Let me give you an example of what i want to achieve but don't know how in image:

Answer 1

You need to call customer collection and filter by each Customer group and then create Custom array which is give data for option array

$CustomerGroups = Mage::getResourceModel('customer/group_collection')->toOptionArray();

$customerArray=array();
foreach($CustomerGroups as $each){
    // get Customer group wise Customer count
     $count=Mage::getResourceModel('customer/customer_collection')
                ->addAttributeToFilter('group_id',$each['value'])->getSize();
     $customerArray[]=array('value'=> $each['value'],'label'=> $each['label'].'(member'.$count.')');

}

$CustomerGroups = array_merge(array('' => ''), $customerArray);

Edit

as per as your request your updated code is below:

$CustomerGroups = Mage::getResourceModel('customer/group_collection')->toOptionArray();

$customerArray=array();
foreach($CustomerGroups as $each){

     $count=Mage::getResourceModel('customer/customer_collection')
                ->addAttributeToFilter('group_id',$each['value'])->getSize();
     $customerArray[]=array('value'=> $each['value'],'label'=> $each['label'].'('.$count.' memeber)');

}

$CustomerGroups = array_merge(array('' => ''), $customerArray);

$fieldset->addField('customergroups', 'select',
        array(
            'name'      => 'customergroups',
            'label'     => Mage::helper('smsnotification')->__('User Group'),
            'class'     => 'required-entry',
            'values'    => $CustomerGroups
        )
    );