问题
Rather typical task but I'm stuck on doing it in a beautiful way.
For example, I need to find the last shipment for each vendor, i.e. to find delivery with the max date for the each vendor
VENDOR DELIVERY DATE
10 00055 01/01/2019
20 00070 01/19/2019
20 00088 01/20/2019
20 00120 11/22/2019
40 00150 04/01/2019
40 00200 04/10/2019
The result table to be populated
VENDOR DELIVERY DATE
10 00055 01/01/2019
20 00120 11/22/2019
40 00200 04/10/2019
I implemented this in a following way, via DESCENDING, which I find very ugly
LOOP AT itab ASSIGNING <wa> GROUP BY ( ven_no = <wa>-ven_no ) REFERENCE INTO DATA(vendor).
LOOP AT GROUP vendor ASSIGNING <ven> GROUP BY ( date = <vendor>-date ) DESCENDING.
CHECK NOT line_exists( it_vend_max[ ven_no = <ven>-ven_no ] ).
it_vend_max = VALUE #( BASE it_vend_max ( <ven> ) ).
ENDLOOP.
ENDLOOP.
Is there more elegant way to do this?
I also tried REDUCE
result = REDUCE #( vend_line = value ty_s_vend()
MEMBERS = VALUE ty_t_vend( )
FOR GROUPS <group_key> OF <wa> IN itab
GROUP BY ( key = <wa>-ven_no count = GROUP SIZE
ASCENDING
NEXT vend_line = VALUE #(
ven_no = <wa>-ven_no
date = REDUCE i( INIT max = 0
FOR m IN GROUP <group_key>
NEXT max = nmax( val1 = m-date
val2 = <wa>-date ) )
deliv_no = <wa>-deliv_no
MEMBERS = VALUE ty_s_vend( FOR m IN GROUP <group_key> ( m ) ) ).
but REDUCE selects max date from the whole table and it selects only flat structure, which is not what I want. However, in ABAP examples I saw samples where table-to-table reductions are also possible. Am I wrong?
Another thing I tried is finding uniques with WITHOUT MEMBERS but this syntax doesn't work:
it_vend_max = VALUE ty_t_vend( FOR GROUPS value OF <line> IN itab
GROUP BY ( <line>-ven_no <line>-ship_no )
WITHOUT MEMBERS ( lifnr = value
date = nmax( val1 = <line>-date
val2 = value-date ) ) ).
Any suggestion of what is wrong here or own elegant solution is appreciated.
回答1:
If not too complex, I think it's best to use one construction expression, which shows that the goal of the expression is to initialize one variable and nothing else.
The best I could do to be the most performing and the shortest possible, but I can't make it elegant:
TYPES ty_ref_s_vend TYPE REF TO ty_s_vend.
result = VALUE ty_t_vend(
FOR GROUPS <group_key> OF <wa> IN itab
GROUP BY ( ven_no = <wa>-ven_no ) ASCENDING
LET max2 = REDUCE #(
INIT max TYPE ty_ref_s_vend
FOR <m> IN GROUP <group_key>
NEXT max = COND #( WHEN max IS NOT BOUND
OR <m>-date > max->*-date
THEN REF #( <m> ) ELSE max ) )
IN ( max2->* ) ).
As you can see I use a data reference (aux_ref_s_vend2) for a better performance, to point to the line which has the most recent date. It's theoretically faster than copying the bytes of the whole line, but it's less readable. If you don't have a huge table, there won't be a big difference between using an auxiliary data reference or an auxiliary data object.
PS: I could not test it because the question does not provide a MCVE.
Here is another solution if you really want to use REDUCE in the primary constructor expression (but it's not needed):
result = REDUCE ty_t_vend(
INIT vend_lines TYPE ty_t_vend
FOR GROUPS <group_key> OF <wa> IN itab
GROUP BY ( ven_no = <wa>-ven_no ) ASCENDING
NEXT vend_lines = VALUE #(
LET max2 = REDUCE ty_ref_s_vend(
INIT max TYPE ty_ref_s_vend
FOR <m> IN GROUP <group_key>
NEXT max = COND #( WHEN max IS NOT BOUND
OR <m>-date > max->*-date
THEN REF #( <m> ) ELSE max ) )
IN BASE vend_lines
( max2->* ) ) ).
回答2:
what do you mean by elegant solution? Using GROUP or REDUCE with the "new" abap syntax is not making it elegant in any way, at least for me...
For me, coding that is easily understandable for everyone is elegant:
SORT itab BY vendor date DESCENDING.
DELETE ADJACENT DUPLICATES from itab COMPARING vendor.
Or if the example is more complex, a simple LOOP AT with IF or AT in it APPENDING aggregated lines to a new itab, will also solve it. Example here.
来源：https://stackoverflow.com/questions/55640273/grouping-aggregation-of-itab-with-table-comprehensions