Long ago - and I am pretty sure the code has been lost to time -
in v2.2.3 (I think) I wrote code to do binary searching on a selection,
as at that time Search Selection (the old command name) was sequential,
but sorting the selection was indexed.
Even with the overhead of managing the pointers, and stepping through
records to find all matching records in the selection, as memory
serves, it was faster (interpretedly) to use the binary search on a
selection size of beginning at 6-8 records.
For those who care, an outline of a binary search (on records in
selection)
The following was written off the stop of my head, in the email editor,
BUT it gets to the basics of a binary search on a selection in 4D.
- get size of selection ($Selection_Size).
- make sure it is sorted on the field you want to search on.
repeat
$Current_record:= int($Selection_Size/2)
repeat
goto selected record([table];$Current_record)
case of
:($Current_record>=$Selection_Size) or ($Current_record<=1)
$Not_Found:=true
:([table]field = Value) // found it create collection of
matching records
add to set([table];"Matching")
$previous:=$Current_record
$Next:=$Current_record
repeat
$previous:= previous-1
goto selected record([table];$previous)
if ([table]field = Value) // found it create collection of
matching records
add to set([table];"Matching")
else
$previous:=0
end if
until($previous=0)
repeat
$$Next:= $Next+1
goto selected record([table];$Next)
if ([table]field = Value) // found it create collection of
matching records
add to set([table];"Matching")
else
$Next:=Selection_Size
end if
until($Next= Selection_Size)
$Mo_More_Matches = true
:([table]field > Value) // Not found current record value >
search value
$Current_record:=int((1+$Current_record)/2)
:([table]field < Value) // Not found current record value <
search value
$Current_record:=int((Selection_Size+1+$Current_record)/2)
end case
until ($Not_Found)) or ($No_More_Mathes)
At this point the set "Matching" contains all records matching the
criteria, or nothing.
On Tue, 18 Jul 2017 22:16:18 +1000, David Adams via 4D_Tech wrote:
>
> And, lest anyone forget, you can use binary search logic on sorted
> selections with GOTO SELECTED RECORD. Why not?
---------------
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