LOOP AT... GROUP BY with dynamic group key

Question

I am trying to loop by grouping data with dynamic group parameter.

We can use dynamic queries on WHERE conditions on loops but I do not know whether it is possible to use a dynamic string in group condition.

Here is the sample where user decides by which field to group and then put additional logic based on the decision:

DATA query TYPE string.
IF i_condition_type = 'ERNAM'.
  query = |ERNAM = MARA-ERNAM|.
ELSE.
  query = |ERSDA = MARA-ERSDA|.
ENDIF.

LOOP AT lt_mara INTO DATA(mara) GROUP BY ( (query) ) "syntax error
                                ASSIGNING FIELD-SYMBOL(<group>).
  LOOP AT GROUP <group> ASSIGNING FIELD-SYMBOL(<line_data>).
    "//do something
  ENDLOOP.
ENDLOOP.

Is there any way to do this? I am also open to other ideas besides grouping because if I can't dynamically group, I will copy so many lines and change only the group key.

Answer 1

As pointed out in the comments, LOOP AT ... GROUP BY doesn't support dynamic group-by clauses from strings.

In this simple example you could create your grouping key dynamically at runtime by creating it with an inline expression like COND or SWITCH:

LOOP AT lt_mara INTO DATA(mara) GROUP BY 
    SWITCH string(
       i_condition_type
       WHEN 'ERNAM' THEN mara-ernam
       WHEN 'ERSDA' THEN mara-ersda
       ELSE ''
     )

But your key-building logic might be too complex to express with an expression (or at least an expression which is still readable by a human being). In that case there is something else you can do: group on values returned by a method:

LOOP AT lt_mara INTO DATA(mara) 
     GROUP BY my_grouping_method( line = mara 
                                  condition = i_condition_type )

The implementation of that method can then include any logic you need to form the grouping key at runtime:

METHOD my_grouping_method.
  IF condition = 'ERNAM'.
    result = line-ernam.
  ELSE.
    result = line-ersda.
  ENDIF.    
ENDMETHOD.

The grouping method can also be a method of a different object. So you could represent your grouping condition as an own class. That would allow you to write code like this:

 DATA(lo_group_condition) = NEW zcl_mara_group_condition( 'ERNAM' ). 

 LOOP AT lt_mara INTO DATA(mara) 
     GROUP BY lo_group_condition->get_key_from( mara )