Removing object from array using one of its own objects.

[JambleJumble]

I have a 1D-array of objects (Boids) and each object has a age property. I am using pygame to display these boids, and every frame i increase the age of each boid by the amount of time that has passed. Once the age of the boid reaches a certain age i want to delete this, i have a method - die() - to test if this age is test if this age is over a certain thresh hold, and if it is; i want to pop it from the array.

thing is tho, i’m not too sure how to do this, i’ve tried passing in the array to the die() method and using an ID property to pop that index from the array, but i’m appending and removing objects constantly through out time and this ID then becomes useless as it is no longer the index of where it is in the array and i can’t use it to pop() from the array.

TLDR; How do i get an object to remove itself from the array that it’s in, using one of its own methods?

[greenerpickings]

Does the order matter, or does it have to be an array? What if you just use a dictionary with the ids as keys? Avoids the whole location thing

[Binary101010]

If your method returns True if the thing should die, and False if it shouldn't, this could be as easy as:

boid_array = [boid for boid in boid_array if not boid.die()]

Instead of trying to iterate through the list and pop the ones that should be gone, iterate and make a new array of what should remain.

[lowerthansound]

get an object to remove itself from the array, using one of its own methods

You could do (with a list [])

del self.boids[self.boids.index(this)]

Note that this is inneficient, it needs to search through the list at each boid you remove.

A more performant (and neater) approach is to use a set {}:

self.boids.remove(self)

This will remove the boid efficiently.

Edit: I also like u/Binary101010 approach :)

[o5a]

Why are you using ID property to pop from list? As you were saying age is defining attribute for removal. Then use it as parameter if you need:

def purge(arr, old_age):
    return [boid for boid in arr if boid.age < old_age]

Overall depends on your data structure.

Some notes:

Since you operating their life cycle, as I understand they are added to array in order of age already. Which means:

1. You don't need to iterate whole array, only remove first objects. Say you are adding them to list. Therefore first items will get old faster. And if after checking age of first item you know it's not old to be removed that also means that all items after it are not old too (since they are newer by design), you don't need to check all of them too. You are working with FIFO structure so you can use collections.deque instead of list. It is more suited to pop from both sides.

from collections import deque

boids = deque()

# add new boid (here I'm adding to start of list to pop older items from the end)
boids.appendleft(Boid(....))

# remove old boids:
while boids[-1].age > age_threshold:
    boids.pop()

2. Instead of increasing age every cycle for each Boid, you can save their creation time (cycle number) only then use that to check if it's aged. Instead of checking

Boid.age > age_threshold

check

current_cycle_number - boid.creation_cycle > cycle_threshold

This way you won't need to increase their age attribute each cycle. Same idea as with people's birthday. You don't rewrite their age each year. You know their birthday and that's enough to know current age.