clear map()
Clears map a.
The result of the function is the number of elements that have been deleted.
Parameters
| 
     Parameter  | 
                
     Description  | 
        
| 
     a  | 
                
     (optional) Name of map. Default: "default".  | 
        
Examples
Assume the are two maps "default" with 10 elements and "my_map" with 15 elements.
| 
     Parameter a  | 
                
     Result  | 
        
| 
     my_other_map  | 
                
     0  | 
        
| 
     | 
                
     10  | 
        
| 
     | 
                
     0  | 
        
| 
     my_map  | 
                
     15  | 
        
| 
     my_map  | 
                
     0  |