Step1:

Create calc as [first letter]

Left([customer name],1)

Step2:

Create parameter and string and list add [first letter]

Step3:

Create 2nd calc as [Selected and others]

if [Calculation1]=[Select Name First letter] then [Customer Name]  else "Others" end

Step4:

Drag this calc into row and show parameter control and select letters.

Step5:

Create new calc as [selected count and others]

if [Calculation1]=[Select Name First letter] then "Selected" else "Others" end

Step6:

Drag this [selected count and others] into row and drag customer name into text and select count.

now we can get selected and other count and also selected customers and others data in view.