Re: LOGO-L> eliminating items randomly from a list

[George Mills <mills@softronix.com>]

Your solution is close but not really random (depending on what's
in the list).
Your solution assumes each element in the list is unique.
Your solution picks a random element but then removes the
first occurance from the left. You can see that trend in the
first run below. Notice that it removed the first 4 "3"'s first
which is not very probably. Pick itself is random but you
don't know what occurance it was.

Note in the second run below it removed some before the
"1" and some after. Because it is now data independent
and strictly position dependent.

The code for both methods is below.
And tweaked for MSWLogo (changed ? to p and replace let with make).

testrem
[3 3 3 3 1 3 3 3 3 3 3 3 3 3 3 3]
[3 3 3 1 3 3 3 3 3 3 3 3 3 3 3]
[3 3 1 3 3 3 3 3 3 3 3 3 3 3]
[3 1 3 3 3 3 3 3 3 3 3 3 3]
[1 3 3 3 3 3 3 3 3 3 3 3]
[1 3 3 3 3 3 3 3 3 3 3]
[1 3 3 3 3 3 3 3 3 3]
[1 3 3 3 3 3 3 3 3]
[1 3 3 3 3 3 3 3]
[1 3 3 3 3 3 3]
[1 3 3 3 3 3]
[1 3 3 3 3]
[1 3 3 3]
[1 3 3]
[1 3]
[3]
[]
[3 3 3 3 3 1 3 3 3 3 3 3 3 3 3 3]
[3 3 3 3 3 1 3 3 3 3 3 3 3 3 3]
[3 3 3 3 1 3 3 3 3 3 3 3 3 3]
[3 3 3 3 1 3 3 3 3 3 3 3 3]
[3 3 3 1 3 3 3 3 3 3 3 3]
[3 3 3 3 3 3 3 3 3 3 3]
[3 3 3 3 3 3 3 3 3 3]
[3 3 3 3 3 3 3 3 3]
[3 3 3 3 3 3 3 3]
[3 3 3 3 3 3 3]
[3 3 3 3 3 3]
[3 3 3 3 3]
[3 3 3 3]
[3 3 3]
[3 3]
[3]
[]

to remItemFrom :anItem :aList
        ;; empty listp output nil
        if emptyp :aList [op [] ]

        ;; if anItem isn't in aList output  aList
        if not memberp :anItem :aList [op :aList]

        ;; if anItem is the first element in aList output the butfirst
of aList
        if equalp :anItem first :aList [op bf :aList]

        ;; other wise create a list (with se) with the first element in
aList
        ;; and call us again with the rest of the list.
        op (se first :aList remItemFrom :anItem bf :aList)
end

to remRandomFrom :aList
        ;; first pick the element to remove

        make "anItem pick :aList

        ;; now remove it

        op remItemFrom :anItem :aList
end

to testrem
   ;; Test old method
   make "foo [3 3 3 3 3 1 3 3 3 3 3 3 3 3 3 3 3]
   repeat count :foo [make "foo remRandomFrom :foo show :foo]

   ;; Test new method
   make "foo [3 3 3 3 3 1 3 3 3 3 3 3 3 3 3 3 3]
   repeat count :foo [make "foo TrueRemRandomFrom :foo show :foo]
end

to TrueRemItemFrom :anItem :aList
   ;; If we have shifted the list down such that the first element
   ;; is the one to be removed then do it
   if :anItem = 1 [op butfirst :aList]

   ;; Shift the element we want to keep over and continue looking
   op (se first :aList TrueRemItemFrom :anItem - 1 butfirst :aList)
end

to TrueRemRandomFrom :aList
   ;; Pick a random POSITION within the list
   make "item (random (count :aList) - 1) + 1

   ;; Remove the element at that position
   op TrueRemItemFrom :item :aList
end



Frank Caggiano wrote:
> 
> Wendy Petti wrote:
> > I have a list with 11 words in it; each is the name of a procedure.  I am
> > trying to pick one of these words at random and then eliminate it from the
> > list.  (At a certain button click, all of the words can be restored to the
> > list.)  But all I can manage to do is either run through the list in the
> > same order as originally entered, eliminating the first (or last) each time
> > (using butfirst or butlast), or select randomly without eliminating any
> > words and sometimes have the same word get chosen repeatedly.  How can I
> > select a word randomly and then place that word at the beginning or end of
> > the list so it can be eliminated?  Or if this is not possible, is there
> > some handy way of entering the list in a newly scrambled order each time a
> > button is clicked?  Does it help to put the list into a text box?
> 
> This will remove a random element from a list
> ;;
> ;; Remove a random element from a List
> ;; Report the updated list
> ;;
> to remRandomFrom :aList
>         ;; first pick the element to remove
> 
>         let [anItem pick :aList]
> 
>         ;; now remove it
> 
>         op remItemFrom :anItem :aList
> end
> 
> to remItemFrom :anItem :aList
>         ;; empty list? output nil
>         if empty? :aList [op [] ]
> 
>         ;; if anItem isn't in aList output  aList
>         if not member? :anItem :aList [op :aList]
> 
>         ;; if anItem is the first element in aList output the butfirst of aList
>         if equal? :anItem first :aList [op bf :aList]
> 
>         ;; other wise create a list (with se) with the first element in aList
>         ;; and call us again with the rest of the list.
>         op (se first :aList remItemFrom :anItem bf :aList)
> end
> 
> You would use it like:
> make "foo [1 2 3 4 5 6]
> show :foo
> -> 1 2 3 4 5 6
> make "foo remRandomFrom :foo
> show :foo
> -> 1 2 4 5 6
> 
> Or
> 
> make "foo [1 2 3 4 5 6 7 8 9]
> repeat count :foo [make "foo remRandomFrom :foo show :foo]
> 1 3 4 5 6 7 8 9
> 1 3 4 5 7 8 9
> 3 4 5 7 8 9
> 3 4 5 7 8
> 4 5 7 8
> 4 7 8
> 4 8
> 4
> 
> Hope this helps.
> Be sure to check out my web site for more logo stuff.
> 
> regards
> --
> Frank Caggiano
> caggiano@atlantic.net
> http://www.atlantic.net/~caggiano
> ---------------------------------------------------------------
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-- 
===============================================================
George Mills
email: mills@softronix.com
http://www.softronix.com
The www page contains some very powerful educational software.
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