Monkey container filtering

[Pixel_OutlawParticipant]

So  I’ve been confused a bit since Monkey X, but what is generally the best way to clear all dead items from a container from various positions?

Do you form a deque and push(pop()) only the alive items to the back on the dequeue [length] many times??

Or do you simply create a new list and add the living items onto it then reassign it back to the old list like in the firepaint example? This seems like it will really hammer memory if you’re clearing dead items out each cycle and creating a new data structure.

Currently I’m working on a Monkey X project (I’ll migrate to Monkey 2 when done) and I need the best container and approach for filtering out many dead instances from the middle.

In many genres of game you’ll have enemies that suddenly have been killed and need to be filtered out from various positions in the container.

I actually think things like Map, Filter, and Reduce would be really nice to have for the containers so you can know they’re implemented efficiently. I’d make them destructive/mutating if possible.

Thanks!
P_O

[nerobotParticipant]

For MonkeyX you can use List<T> container and call its Remove() method like this:

Monkey

Import mojo Function Main() Local list:=New List<GameObject> list.AddLast(New GameObject("one",True)) list.AddLast(New GameObject("two")) list.AddLast(New GameObject("three")) list.AddLast(New GameObject("four",True)) ' filtering For Local obj:=Eachin list If obj.dead Then list.Remove(obj) Next For Local obj:=Eachin list Print "obj: "+obj.name Next End Class GameObject Field dead:Bool Field name:String Method New(name:String,dead:Bool=False) Self.name=name Self.dead=dead End End

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Import mojo   Function Main() Local list:=New List<GameObject> list.AddLast(New GameObject("one",True)) list.AddLast(New GameObject("two")) list.AddLast(New GameObject("three")) list.AddLast(New GameObject("four",True)) ' filtering For Local obj:=Eachin list If obj.dead Then list.Remove(obj) Next   For Local obj:=Eachin list Print "obj: "+obj.name Next End     Class GameObject Field dead:Bool Field name:String Method New(name:String,dead:Bool=False) Self.name=name Self.dead=dead End End

In Monkey2 we can write more powerfull code – because we can pass functions as parameters of other functions.

And we can write generic function to remove items by filter for any instance type.

Monkey

Function RemoveInList<T>:Int( list:List<T>,filteringFunc:Bool(T) ) Local count:=0 Local it:=list.All() While Not it.AtEnd If filteringFunc( it.Current ) it.Erase() count+=1 Else it.Bump() Endif Wend Return count End ...... Local list:=New List<Int> For Local i:=0 Until 20 list.Add(i) Next Local filter1:=Lambda:Bool(val:Int) Return (val Mod 4) = 0 End Local filter2:=Lambda:Bool(val:Int) Return val>10 And val<14 End RemoveInList( list,filter1 ) For Local i:=Eachin list Print i Next RemoveInList( list,filter2 ) 'just pass other filter func For Local i:=Eachin list Print i Next Local list2:=New StringList( New String[]("one","two","three") ) Local filter3:=Lambda:Bool(val:String) Return val.Length<4 End ' now use it for strings RemoveInList( list2,filter3 ) For Local i:=Eachin list2 Print i Next

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Function RemoveInList<T>:Int( list:List<T>,filteringFunc:Bool(T) )   Local count:=0 Local it:=list.All() While Not it.AtEnd If filteringFunc( it.Current ) it.Erase() count+=1 Else it.Bump() Endif Wend Return count End   ......   Local list:=New List<Int>   For Local i:=0 Until 20 list.Add(i) Next   Local filter1:=Lambda:Bool(val:Int) Return (val Mod 4) = 0 End   Local filter2:=Lambda:Bool(val:Int) Return val>10 And val<14 End   RemoveInList( list,filter1 )   For Local i:=Eachin list Print i Next   RemoveInList( list,filter2 ) 'just pass other filter func   For Local i:=Eachin list Print i Next   Local list2:=New StringList( New String[]("one","two","three") )   Local filter3:=Lambda:Bool(val:String) Return val.Length<4 End   ' now use it for strings RemoveInList( list2,filter3 )   For Local i:=Eachin list2 Print i Next

One bad thing here – we can’t write the only universal function for all containers (list, stack, map, etc…) because of language limitation:

Finally, IContainer is not a ‘real’ interface because Monkey2 does not yet support generic interface methods. This feature is planned for a future version of monkey2.

[Pixel_OutlawParticipant]

Ah, that’s really interesting.
Thanks for the insight!

For your Monkey X example:
Are you sure calling remove on the iterator is safe?
It’s been a source of dangerous and undefined behavior in many programming languages.
Just a surprising pattern to see if so.

As far as passing functions:
Yep! I anticipate using passed functions quite a bit in Monkey 2.  I’m very familiar with that style of programming.
I do it quite a bit in C++, Python, Common Lisp.

[Simon ArmstrongParticipant]

Remove seems safe inside a for next, not sure if there are other iterations available for monkey containers.

Monkey

#Import "<std>" Using std.. Function Main() Print "delete test" Local list:=New List<String>() list.AddLast("one") list.AddLast("two") list.AddLast("three") For Local i:=Eachin list If i="two" Then list.Remove(i) Print i Next End

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#Import "<std>" Using std.. Function Main() Print "delete test" Local list:=New List<String>() list.AddLast("one") list.AddLast("two") list.AddLast("three") For Local i:=Eachin list If i="two" Then list.Remove(i) Print i Next End

[nerobotParticipant]

Are you sure calling remove on the iterator is safe?

I know that other langs deny iterator changes, but I just tried it in monkey-x and it works.

In monkey2 don’t work but we have iterator.Erase() here.

[Pixel_OutlawParticipant]

Ok, thanks for the help guys!

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