Qlik Script Sub KeepFields to Drop mass fields

KeepFields.qvs

Sub KeepFields(Fields,TableName)
  Let n = NoOfFields('$(TableName)');
  Set d = #;
  For i = 1 to $(n)
      Let f = FieldName($(i), '$(TableName)');
      If Index('$(Fields)', ',$(f),') = 0 then
          If '$(d)' = '#' then
              Let d = '$(f)';
          Else
              Let d = '$(d),$(f)';
          End if
      End if
  next
  If '$(d)' <> '' then
      Drop Fields $(d);
  End if
End Sub

//Example:
//Call KeepFields(',CUSTOMER_ID,NAME,ADDRESS,PHONE,', 'Customer');