Selected Line Only

[Doug Easterbrook]

hi Martin.

people have touched on various ways to process selected lines in a list.    Thise is stuff I’ve found to be useful in my past


option 1:   For each line in list

advantages ..

1) tends to be faster than processing selected lines using option 2 (at least in historical benchmarks, I haven’t redone benchmarks in a few years to see if the notation version has improved in performance
2) uses a reversible block to restore the current list and line number when finished

disadvantage.

1 loops within loops processing multiple lists .. not so easy


begin reversible block
   set current list as myList
   calcilate myList.$line as myList.$line
end reversible block

For each line in list (Selected lines only) from 1 to myList.$linecount step 1


end for






option 2.  using notation, looping to only look at selected lines

Major  advantage:

you can do loops within loops processing lists
you can process selected lines
you can process selected lines in reverse order
you can add a filter that must match lines in order to be processed.


ie: the  ktrue parameter in $first and $next .  says selected lines only.  very useful to make it go faster
there are other parameers in the $first and $next to process the loop backwards and add filters


calculate orginalLine as mylist.$line

do myList.$first(ktrue) returns booleanFlag
while booleanFlag



   do myList.$next(0,ktrue) returns booleanFlag
end while

calculate mylist.$line as orginalLine





Option 3:  where you only care about the selected lines and want to do a bunch of work with them, never putting anything back into them


calculate templist as myList
do templlist.$remove(klistkeepselected)
for templist.$line from 1 to templist.$linecount

end for


or the notation version — which, I confess, I don’t use often — I prefer the above  ‘for’ construct

calculate templist as myList
do templlist.$remove(klistkeepselected)
do templlist.$first() returns booleanFlag
while booleanFlag

   do templlist.$next() returns booleanFlag
end while





These days, when I process selected lines in a list, expecially in table classes and for code safety, I use the $first(ktrue) and $nect(0,ktrue) approach

do myList.$first(ktrue) returns booleanFlag
while booleanFlag

   do myList.$next(0,ktrue) returns booleanFlag
end while


hope that helps.


Doug Easterbrook
Arts Management Systems Ltd.
mailto:doug at artsman.com
http://www.artsman.com
Phone (403) 650-1978

> On Jul 10, 2022, at 1:20 PM, Martin Obongita via omnisdev-en <omnisdev-en at lists.omnis-dev.com> wrote:
> 
> Hi Friends, What is the syntax for "Selected lines only" in the FOR loop statement, For each line in list from 1 to iDataList step 1?
> 
> _____________________________________________________________
> Manage your list subscriptions at https://lists.omnis-dev.com
> Start a new message -> mailto:omnisdev-en at lists.omnis-dev.com