Easy way to Sort Subfile data:

Sorting data is something RPG programs often need to do. If it's just a simple single field array you're sorting in order to use the much faster binary search possible with %Lookup, for example, then SORTA works well and is simple. But what if it is a more complex task like sorting the data in a subfile on a user-selected column? Surely you need some more involved techniques, such as retrieving the data from the database again using a different ORDER BY on an SQL SELECT statement or using a different logical file or you could use the qsort C function for sorting the array elements in the program. Something as simple as SORTA can't be used for that, right?
Maybe so. The circumstances where this is effective are limited, for sure, but if your requirements fit, then using SORTA with a group field can be the simplest way and often a faster alternative than other methods you may have tried.
First of all, what's a group field? It's a field in a data structure that is broken down into smaller subfields. For example, group field SflData might be made up of information about products (name, price, quantity) by using the Overlay keyword, such as:
D SflDS Ds Inz
D SflData Like(SflRecData)
D Dim(999)
D Name Like(ProdDS)
D Overlay(SflData)
D Price Like(SellPr)
D Overlay(SflData:*Next)
D Qty Like(STOH)
D Overlay(SflData:*Next)
The effect is similar to nested data structures, except without the requirement to use qualified names. (Likewise, there are many limitations on group fields because of the lack of name qualification.) One additional thing that's nice about group fields compared to nested DSs is that we can use SORTA against any of the subfields in a group field array.
So this means if I wanted to sort the data in the SflData array by product name, I could do that with the following statement: SortA Name;. Much simpler than any of those other options I mentioned above! Of course, in nearly all cases, it would require the use of the built-in function %SubArr (substring array) because I'm not likely to have filled up all 999 elements of SflData. Even so, the entire bit of logic to accomplish sorting this subfile data in the sequence of any of the three fields could be as simple as:
If SortByName;
SortA %SubArr(Name:1:Count);
ElseIf SortByQty;
SortA %SubArr(Qty:1:Count);
ElseIf SortByPrice;
SortA %SubArr(Price:1:Count);
EndIf;
This technique is very simple and in most cases quite a fast way to sort subfile data (or any other kind of repeating data). It does have significant limitations. For example, you can only sort on one subfield at a time. (Of course, you could group two subfields together if they happen to be adjacent in the subfile record.) Also, you must be able to retrieve and store all the data destined for the subfile into an array so that you can sort it all together. For some very large subfiles, that won't be practical. But for those occasions where it works, it couldn't get much simpler.