# Eight different sort algorithms implemented in ABAP

Some application developers think that it is enough to know SORT keyword and how to use sorted table in ABAP for their daily work without knowing how SORT is done internally. For me I can not say this assumption is wrong. I personal preference is to know something more thoroughly. We have learned various sort algorithms in the university, here I just list my implementation on some of them using ABAP for my personal study purpose.
For each sort algorithm I will create a static public class with a sort method which accepts an internal table with unsorted Integer and an output table which are sorted. For simplification reason the element in the internal table only consists of unsigned integers ( >= 0 )

# Bucket Sort ( In China we prefer to call it Hash Sort )

In ABAP the internal table is a perfect choice for bucket collection 🙂 A small trap here is, array in most program language has start index as 0, however in ABAP for internal table it is 1. So be careful about the possibility that 0 appears in the input internal table.
And I also implement a version using JavaScript which can support negative integer in Bucket Sort as well. See source code here.

# Bubble Sort

I have implemented two variants, the only difference between them:
• Variant 1 uses two nested DO LOOP, while variant 2 uses WHILE as inner LOOP.
• Variant 1 uses traditional keyword MODIFY itab FROM workarea INDEX index to swap the two adjacent element, while variant 2 uses new grammar itab[ index ].
Source code for both variants.

# Merge Sort

Again I have implemented two variants.

## Variant1 – use Recursive

Callstack could be found below: ## Variant 2 – non recursive version

This variant is implemented in a non-recursive way. Source code of both variants.

# A very draft performance comparison

Since each sort algorithm has different time complexity – best case, worst case and average case according to different data distribution, here below I only make a very draft comparison by generating some random integers in ABAP via cl_abap_random_int:
``````DATA: lv_seed TYPE i.
lv_seed = sy-timlo.
DATA(lo_ran) = cl_abap_random_int=>create( min = 1 max = 1000 seed = lv_seed ).
DO iv_num TIMES.
APPEND lo_ran->get_next( ) TO rv_table.
ENDDO.``````
Meanwhile I am especially curious about how ABAP keyword SORT will behave against these eight sort algorithms, so I create another two sort approaches.

## The ninth sort approach

Pretty simple, just use ABAP keyword SORT to sort the table.
`````` method SORT.
rv_table = iv_table.
SORT rv_table.
endmethod.​``````

## The tenth sort approach

I just loop the original table and put each element to a sorted table with line item as INT4.
``````DATA: lt_sorted TYPE ZTSORTED_INT4.
LOOP AT iv_table ASSIGNING FIELD-SYMBOL(<item>).
INSERT <item> INTO table lt_sorted.
ENDLOOP.
APPEND LINES OF lt_sorted TO rv_table.``````
The table type ZTSORTED_INT4 has line type INT4 with sorted table type. Test code:
``````DATA(lt_test_data) = zcl_sort_helper=>generate_data( 3000 ).

zcl_sort_helper=>start_measure( ).
DATA(lt_bubble) = zcl_bubblesort=>sort( lt_test_data ).
WRITE: / 'Bubble Sort duration:' , zcl_sort_helper=>stop( ).

zcl_sort_helper=>start_measure( ).
DATA(lt_hashsort) = zcl_hashsort=>sort( lt_test_data ).
WRITE: / 'Hash Sort duration:' , zcl_sort_helper=>stop( ).

zcl_sort_helper=>start_measure( ).
DATA(lt_heapsort) = zcl_hashsort=>sort( lt_test_data ).
WRITE: / 'Heap Sort duration:' , zcl_sort_helper=>stop( ).

zcl_sort_helper=>start_measure( ).
DATA(lt_insertsort) = zcl_insertsort=>sort( lt_test_data ).
WRITE: / 'Insert Sort duration:' , zcl_sort_helper=>stop( ).

zcl_sort_helper=>start_measure( ).
DATA(lt_mergesort) = zcl_mergesort=>sort( lt_test_data ).
WRITE: / 'Merge Sort duration:' , zcl_sort_helper=>stop( ).

zcl_sort_helper=>start_measure( ).
DATA(lt_quicksort) = zcl_quicksort=>sort( lt_test_data ).
WRITE: / 'Quick Sort duration:' , zcl_sort_helper=>stop( ).

zcl_sort_helper=>start_measure( ).
DATA(lt_selectsort) = zcl_selectsort=>sort( lt_test_data ).
WRITE: / 'Select Sort duration:' , zcl_sort_helper=>stop( ).

zcl_sort_helper=>start_measure( ).
DATA(lt_shellsort) = zcl_shellsort=>sort( lt_test_data ).
WRITE: / 'Shell Sort duration:' , zcl_sort_helper=>stop( ).

zcl_sort_helper=>start_measure( ).
DATA(lt_sort_keyword) = zcl_sort_via_keyword=>sort( lt_test_data ).
WRITE: / 'ABAP Sort keyword duration:' , zcl_sort_helper=>stop( ).

zcl_sort_helper=>start_measure( ).
DATA(lt_sort_table) = zcl_abap_sorttable=>sort( lt_test_data ).
WRITE: / 'ABAP Sorted table duration:' , zcl_sort_helper=>stop( ).
ASSERT lt_bubble = lt_hashsort.
ASSERT lt_hashsort = lt_heapsort.
ASSERT lt_heapsort = lt_insertsort.
ASSERT lt_insertsort = lt_mergesort.
ASSERT lt_mergesort = lt_quicksort.
ASSERT lt_quicksort = lt_selectsort.
ASSERT lt_shellsort = lt_selectsort.
ASSERT lt_sort_keyword = lt_shellsort.
ASSERT lt_sort_table = lt_sort_keyword.``````
The test result ( unit: microsecond ) The ABAP SORT keyword and SORTED TABLE did a really good job here 🙂
The complete source code for this blog could be found from my github.

# Sleep Sort in JavaScript

Last but not least, the super cool “Sleep Sort” done in JavaScript, which does not need any comparison against two elements in the array.
``````const num = [1,5,6,11,2,3,4,8,7,14];
num.forEach( num => {
setTimeout( () => { console.log(num)}, num);
});``````

Test output: Happy coding 🙂

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• Thanks for sharing with us , it is really helpful.

• Thanks for sharing.

However, I must wonder: Are there any real use cases for manual sort in ABAP?

• Jerry Wang Post author

Hi Shai,

As far as I know, the answer is no. As least for me, I never use the manual sort in my application development, the keyword SORT does a good job enough. I implement these eight algorithm for fun, just in order to refresh what I have learned in my university. In China when graduates are looking for job, they are tended to be asked to write implementation out in paper or white board 🙂

Best regards,

Jerry

• Thanks for sharing. Good thought…

• Thanks for sharing! Very cool!!! …..and it really bothers me when people as “yeh, but why are you doing this? when would you ever use this is in the real world?”……Hey Debbie Downer, what is wrong with doing it for FUN ??!?! I know….crazy concept, right?!?! Some people actually do have fun just coding and seeing what they can create/re-create/do with it…….so kudos to you for that!!!

• thanks for the explanation

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