get next object in list that is red

BlitzMax Forums/BlitzMax Beginners Area/get next object in list that is red

slenkar

(Posted 2008) [#1]

if i had a list of ships
how would I get the next one in the list that had a colour field of "red"

also if the one I have selected is the last red one on the list

how do I get the first red one on the list ?

e.g.
type ship
global list
field colour$
endtype

Perturbatio

(Posted 2008) [#2]

you could either:

use EachIn to iterate through the list and look for red ones (the first one you find would be the first in the list).

or:

have a separate list for each colour

or (if you're insane) have a separate type for each colour and then iterate with:

For Local ship:TRedShip = EachIn MyBigShipList
	print ship.name
Next

that would only select ships that inherited from the TRedShip type

tonyg

(Posted 2008) [#3]

You could keep a record of the last list item checked plus a count of how many items on the list and do a for/loop with a ValueAtIndex command or go down to the TLINK level and use NEXTLINK, LASTLINK and FIRSTLINK

slenkar

(Posted 2008) [#4]

thanks Ill have to delve into the link commands

dmaz	(Posted 2008) [#5]

I did this a while back, hope it helps.
http://www.blitzbasic.com/codearcs/codearcs.php?code=1807

it allows

local list:TListF = new TListF
for blah:yourtype = eachin list.From(start:TLink,howMany:int=-1)

for blah:yourtype = eachin list.ReverseFrom(start:TLink,howMany:int=-1)

for blah:TLink = eachin list.LinksFrom(start:TLink,howMany:int=-1)

if howMany is -1 then it will continue to the end or the begining as in the case of ReverseFrom.

slenkar

(Posted 2008) [#6]

I get an error when I try to run the demo and the example program

attempt to access null object
on this line:
Return (_link._value<>_link) And _howMany

dmaz	(Posted 2008) [#7]

whoops... that's because I left some test code in... just comment out the line

t.list.Clear

near the bottom. or just recopy the code.

Retimer

(Posted 2008) [#8]

have a separate list for each colour

Yeah, I would go with using seperate lists for each color, if you really want to go the list route.

If you're iterating through a list to find a 'red' item, having this in a loop is going to slow things down quite a bit, otherwise I guess it can't hurt.

You can take out the whole sorting process just by having seperate lists, as you will only require the first item in the list, instead of looking for the first item with X attribute in the list.

slenkar

(Posted 2008) [#9]

i can 'select' ships so I could select the fifth one and then need the next one, i spose i could use nextlink for that.

dmaz	(Posted 2008) [#10]

yes, if you have the link. in my types I always have a field called link so that I can do that among other things.... make sure you have and call a remove method to remove the object.

example

Type TObject
	Global list:TList = New TList
	
	Field link:TLink
	Field x:Int
	Field y:int
	
	Method New()
		link = list.AddLast(Self)
	End Method
	
	Method Remove()
		link.Remove
	End Method
	
End Type

Beaker

(Posted 2008) [#11]

Aren't you are asking for serious problems doing that? Circular references etc?

dmaz	(Posted 2008) [#12]

no.... not with the example above
anyway, that's why you put all your clean up in the one method. you should also add in the method
super.Remove
if appropriate.

if you have any references to other objects, this is where you would null them out to prevent a circular reference problem. you don't need to null "link" because link.Remove breaks the chain by nulling it's object reference.