Sorting an (dynamic) array

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1

Dear fellow Natural developers :slight_smile:

What is the best (fastest) way to sort an (dynamic) array in Natural? I use code like the following:

DEFINE DATA
*
PARAMETER
01 #ARRAY (A/1:*) DYNAMIC
*
LOCAL
01 #NUMBER-OF-ELEMENTS (I4)
01 #ARRAY-TEMP (A/1:*) DYNAMIC
01 #ELEMENT (A1000) /* DYNAMIC is not allowed with SORT!
01 #A (I4)
01 #T (I4)
*
END-DEFINE
*
********************************************************************************
DEFINE SUBROUTINE SORT-ARRAY
********************************************************************************
*
#NUMBER-OF-ELEMENTS := *OCC(#ARRAY)
IF #NUMBER-OF-ELEMENTS EQ 0
  ESCAPE MODULE
END-IF
*
RESIZE ARRAY #ARRAY-TEMP TO (1:#NUMBER-OF-ELEMENTS)
#T := 0
*
FOR #A 1 #NUMBER-OF-ELEMENTS
  #ELEMENT := #ARRAY(#A)
END-ALL
*
SORT BY #ELEMENT USING KEY
  ADD 1 TO #T
  #ARRAY-TEMP(#T) := #ELEMENT
END-SORT
*
RESET #ARRAY(*)
#ARRAY(*) := #ARRAY-TEMP(*)
*
END-SUBROUTINE
********************************************************************************
*
END

This works but I don’t know if it really is the best possible way. Especially when sorting a multi-dimensional array I need a temp field for every original field in the array and this is very error prone:

FOR #C 1 ARRAY.NUMBER-OF-ELEMENTS
  #KEY-SORT := ARRAY.KEY
  #VAR1-SORT := ARRAY.VAR1(#C)
  #VAR2-SORT := ARRAY.VAR2(#C)
  ...
END-ALL
*
SORT BY #KEY-SORT USING
    #VAR1-SORT
    #VAR2-SORT
    ...
END-SORT

Is there a better way to sort an array?

Best regards,
Stefan

2

Hi Stefan,

You really do not need a temp array at all.

See the code below:

DEFINE DATA
local
01 #A (I4)
01 #T (I4)
1 #array (n2/1:10) init <2>
1 #temp (n2)
*
END-DEFINE
*
for #a = 1 to 10
move #array (#a) to #temp
end-all
sort by #temp using keys
add 1 to #t
move #temp to #array (#t)
end-sort
write #array (*)
end

If you run this you will see it work quite well.
Basically, internally, Natural creates an array which is your temp-array.
After the SORT, you are getting successive values back from the sort; that is, you are getting successive values of what you call temp-array.

For a multi dimensional array all you need is something like:

DEFINE DATA
local
01 #A (I4)
01 #B (i4)
01 #T (I4)
1 #array (n2/1:10,1:5) init <2>
1 redefine #array
2 #aaa (n2/1:50)
1 #temp (n2)
*
END-DEFINE
*
for #a = 1 to 10
for #b = 1 to 5
move #array (#a,#b) to #temp
end-all
sort by #temp using keys
add 1 to #t
move #temp to #aaa (#t)
end-sort
write #array (*)
end

I haven’t run the 2 dim example (did run the 1 dim), but it should work.

Also, the code above should be easily adaptable to DYNAMIC.

steve

3

Dear Steve,

thank you! That definitely reduces the amount of code needed for this simple task :slight_smile:

Best regards,
Stefan