ARRAYLIST VS LINKEDLIST
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- čas přidán 15. 03. 2024
- In this one, we explore how ArrayLists and LinkedLists works at memory level and how scripting languages handle their "arrays."
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20:34 Fuck I need that card in my wallet
Me too, I hope he sells it as merch one day
best animation quality yet, the pointer hell is somehow very understandable
This is the single best video on the topic ever! When i was studying cs, our prof didn't even try explain how data is stored, he just moved on to using pointers, i had no previous experience with them and was like wtf are pointers. You put it all flawlessly into words AND animations, and a picture is worth a thousand words. Great video that brings so much clarity, every cs undergrad needs to see this. Thanks a lot!
baby wake up core dumped just uploaded
🤣lmao seriously tho
I prefer 'baby wake up core dumped'
Nitpick: JavaScript engines typically do implement arrays as continuous blocks of data, and generally setting just one item at index 10k will then allocate up to that number (or more). They just have to pessimise the array for the holes in it.
I remember writing a filter and it was returning null items, you have to be very careful with JS
They use C++ struct arrays, not normal arrays, class arrays or vectors.
What a spectacular video, I'm just creating my own programming language and this fits me like a glove.
absolutely one of the best channels out there right now. u go even more indepth than some of my college classes and make it seem easy. big ups bro
Just found your channel! Really happy to see you just uploaded. I love your intuitive visuals to explain all sorts of mechanics
I remember really struggling with these sorts of topics when I was at university. These are some of the best explanations for OS/low-level programming concepts I've ever come across!
yes, I am to watch a livestream of yours solving CodeCrafters challenges
Jon had done the same a week ago with Git, and I watched through the entire thing. that was indeed really interesting, and I'd like to solve these myself too 😊
Waited for this video after the previous teaser. Ur videos are the most accurate on the subject there are
you've mentioned about thinking to solve codecrafters challenges on stream.
Yes please!
Incredible work with these videos so far. Hitting all the key points at just the right level of detail. The animation work is just... * chef's kiss * Keep it up 🙌
One of the best videos I ever watched in my life
I learn so much deim your videos!! Thanks a lot !!! I'm waiting for the next one!
this content is pure gold!
I wasn't able to leave a comment on your post from yesterday but I guessed arrays and I was right! I love these deep dives
Love the quality of the videos I will recommend other people in my class to them because they’re concise and easy to understand. Keep it up!
Amazing as always
Would love to watch those streams
I've been working with Java for almost 20 years, and I don't think I've ever thought about what happens when you remove an element from an ArrayList.
Thanks for the eye opener.
Me too, but with Go. Now I understand the motivation for slices vs arrays
I recommend everyone starting to understand the data structure to subscribe this channel and save this video, well done very nicely demonstrated!
Great videos, thank you for your efforts!
This channel is about to blow up🎉
George, your videos are really awesome! I already knew all these concepts but I have never seen them better explained. Anyway, I love C and Assembler because they are teaching how computers work...😊
Very good video, this is the kind of teaching that works for me so thank you
Javascript bashing ✅
Engaging and interesting systems programming content ✅
Funny retorts for armchair programmers ✅
Im so glad i found this channel early and subbed
Thanks for the knowledge!
What a fantastic video! Now all I want is to program in Assembly to learn how really an computer works, and to optimize all those inefficiencies those languages introduce!
Great presentation 👌
Hi, the video has been pretty interesting so far. Just a suggestion: please put the link to the previous videos you recommended. Otherwise, in a year or so, it will be much harder to find. Unfortunately, CZcams showed exactly where the current video is in the channel's timeline.
i love that little departure to interpreted language land
I have yet to see the combination of a linked list and array list in the wild that I was taught in my AlgoDat course and never again afterwards. It stored the data in a big array that can be relocated to grow, but also a separate mapping from indexes to array offsets. That sounds like a linked list (just with array indexes instead of full pointers) that enforces some form of memory coherence for both list nodes and data. As far as I know, you can refine this concept to a linked list of array slices, which is how text editors support efficient cutting and pasting of text.
that's why i propose all scripting languages should be pseudo compiled: the bytecodes are as specific as assembly instruction (not as much but you get it), and the generic stuff actually happens at "compile" time, every scripting languages should do that, even at the cost of longer "compile" time. I want to do one, but I struggle everytime when making the parser so you will probably never see that.
Also in java, if it's not a primitive, it's an object, every arrays of non-primitives in java are arrays of objects, and you can verify it with the JNI.
About 17:45, I'm no great expert on system programming, but the severity of data locality is unlikely severe. The cost of pointer-based array instead of a template array resides in the unpredictable position of object allocation, which confuse the CPU cache prefetcher. In reality, most workload allocates objects (as each object in the containing array) closely or in a predictable fashion, so prefetching works adequately well. And of course, pointers are still grouped together as always.
For example, if we add items to a list in a loop, it is trivial for the CPU prefetcher to assume the next approriate location. Hotspot specifically, each thread has its own thread heap, so as long as the array/list is not multithreaded (which is unlikely), the pattern will be maintained. Moreover, with the nature of GC, the compacting phase will very likely move spreaded objects all over the heap to a single location, both avoiding fragmentation and maintaining the fetch pattern.
There are exceptions, like if a BaseType array could contain both DerivativeType1 and DerivativeType2 with completely different object layout (only possible with reference-based array), then it's difficult for the CPU to make a good sense of the fetch pattern, which will likely suffer from "data locality". But as always, the template array would also suffer from this, so it's rather an unfortunate universal technical difficulty.
Wow, so informative, thanks so much. I’d watch a live coding session.
Thank you so much for this video, excellent explaination! I have a question, though: as you showed, in languages like Rust, besides specifying the array's size, it's also necessary to specify the data type (integer, float, etc...), and from what I understood, it's because this way the compiler already knows how many bytes to read for each element. However, at 19:45, in the case of Python, how does the interpreter know if, once a pointer is dereferenced, the retrieved object is an integer, a string, or another element with indefinite length? Because according to your (beautiful) animation it seems like every object has it's own specific size.
Interpreters attach 'tags' to values in memory, so when the value is needed, it first reads the tag to identify the type of the value and know how many bytes to read.
The answer is explained in my video: The size of your variables matters.
I did try to use the *void pointer once! It was hilarious when you mentioned it
You are back🎉
Yes , really good
Heeeesss baackkk
The content is great.
Would be interesting to see your overviews about how rust's compiler works and about compilers theory in general. As well as interpreters actually.
This is incredible
Excellent!
You are very good please continue like that and I will be happy if you touch on the assembly perspective of the things too 😄
This was indeed a banger
Amazing video!
amazing video!
I would have never suspected that an IT person can actually explain something well enough for people to understand. Good job buddy
The reason why most programmers are bad at explaining things, is that they don't fully understand most of the things they would try to explain. And the reason for that, is that most of the time they were given a surface level explanation themselves, and they just accepted it.
@@tonchozhelev EXACTLY
Programmers and IT people aren’t the same
@@vimandmanyothers554 it shouldn't be the same, i agree, but sadly the line is very blurry these days. a lot of programmers nowadays have no real clue what their code is actually doing, all they care about is whether it works or not. this stems from the overly-corporate nature of the modern internet and digital world. as long as it gets them money on the short term, who cares if it's performant, well-written, robust code? the mindless consumers certainly don't, so why should the multimillion dollar companies care? sad world we live in
@@tonchozhelev I have en education in embedded systems and having watched all the few videos they've done so far I've already learned several important things that no-one bothered to explain about how different data-structures are implemented by the compiler and why/how that has significant performance implications.
What a gem of a channel. Keep it up!
Good content, thx!
It should be pointed out that the cache behavior of linked lists is NOT inherit to the linked list structure but rather to the allocator used to allocate the nodes. If we have an allocator allocators linearly the nodes will be located in memory in exact the same way as with the array. Alternative approach is to store enough elements in each node so that a full cache line is always used. Removal and addition from the middle of a node can be solved with splitting and merging.
Also I am certain that pretty much all javascript interpreters really do use arrays whenever possible and only resolve to hash map as a fallback when the wasted size is too much or keys are some other type than numbers. This is not too difficult to implement internally and the performance boost is significant.
This is very important to note. I also think iv read v8 uses property access for very small and likely to not be modified arrays. This way it can do direct property access without hashmap lookup or array indexing.
The early bird gets the typo
Fixed, thanks :D
@CoreDumpped
Thank you for all the effort you put into crafting explanations + animations even a newbie like me can grasp so easily 🙏
Maybe it would be better to say that modern JS JIT compilers, like V8, often optimize arrays?
love your videos
Amazing video. And thank you for not pedaling surfshark or some unrelated crap. Video bookmarks would be welcome!
You are doing revolutionary work bro
Keep going ,keep posting more often
no need to be so self-conscious at the end there. this channel is great
another great video
your content is 👑. my kids will study from this channel one day 🥹 and their kids 😇 and their kids kids for generations learning low level concepts and rust. 🥂
Really great video, although I would have liked it if you talked about bounds checking in a normal array when you were talking about indexing out of bounds
12:03 did you cousin also write a getter for "self.lenght" (of self.items[self lenght]) to be the same value as "self.length" ?
Please do Hashmaps next and how are its elements linked and how does it look like in memory
Omg I loved this video. Super cool to know how python’s list works under the hood. Can’t wait for what you’ve got next!
Thanks. I had always assumed ArrayList was just some sort of alias for a Deque, but now I know, it's just a dynamic array type. Java is one of those languages that I've avoided fully learning and any language that reuses that name for a container type too. As it is now, I probably have far too much knowledge of Java.
More reasons to hate JS :D
(And yes to the streams)
Also if you intend to expand your community on other platforms a discord server might be a good idea too.
absolute mad lad
Yet another banger from project CD!
“This explains why we use zero instead of one for the first element”
What a hero 🙌. Finally a non-stupid “programmers just count from zero” explanation
Excellent videos. Love your channel!
God please never stop making vids my guy AGHHHHHHHHHHH
The Lua Table has entered the arena.
It would be interesting to see what Lua’s cache hit & miss rate is compared with other languages…
Thankyou so much for these videos plz keep making them they are so good
i recommended the first 3 videos in this series to some computer science students i was tutoring because i felt like they went in depth into these concepts, while at the same time using terms and concepts that beginner programmers are familiar with. i felt like this video used a lot more terms and concepts which might be difficult for beginner programmers to understand compared to the last three. i think this series would be better for introductory students if the smaller concepts mentioned in this video like data structures, time complexity, etc. had heir own video before having a video about dynamically sized collections
in other words i felt like the pacing in this series took a sharp turn that might be too overwhelming for me to be able to recommend it to other computer science students. judging by the pacing of the first three videos in this series, it seemed like these videos were attempting to cater toward beginner-intermediate programmers with around a year of experience, but this video didn’t come across that way, although i may be wrong in my assumption for the targeted audience of these videos
@@sa-hq8jk I think there is enough context to understand what a datatype is without giving the textbook definition of what a datatype is (which i doubt will be helpfull to anyone anyway). A definition of time complexity would probaply have been nice, it is easy to understand and aply in these cases and can also easily be googled if needed.
@@someonespotatohmm9513 i didnt mean what exactly a data type is, but more of how a struct is a type which combines other types, and how they are grouped together in memory and interpreted by the compiler and by memory
i wish i had the opportunity to access all these kind of videos when i was studing computer science!
Me too!
Very well explained, these kinds of animations are extremely useful.
I think when he says ‘and so Forth’ he’s actually telling us what programming language to use.
😂
We are 2 orange S
In Lua arrays are done the same way as in JS: they are in fact maps with values being indexed by numeric indices
Man this animations
Where were they for all these years?
I created a linked list in C with two levels of indirection with varying orders of magnitude up to a billion elements. However, I never got valgrind to report cache misses above 0.7% when pushing all, then accesseing all then popping all. I understand that valgrind will report a simulation of the cache rather than the actual cache, but it was the best I could do to measure because my kernel does not have perf.
Thanks
pointer arithmetic was baked directly into intel 8086 cpu instruction set, no wonder systems programming langugaes at the time would also reflect the feature in their syntax
Does this has anything to do with that take that I've been recently reading a lot claiming that C beats everything because CPUs are designed to be 'C-compiled code' efficient?
Nice.
If only I had you as my professor
Your cousin may know more than me, but he still misspelled "length" in that code :P 11:50
Thanks for your hard work!!!🎉
There‘s no way i was too lazy to comment „Dynamically sized data structures“ on yesterday’s post 😂 I had it 😭😭
which tools are you using to create these animations. looks pretty good
Be aware that modern javascript engines optimises arrays if they have no holes (java like) and even more if they are of the same type (c like) : check for SMI, DOUBLE_SMI, HOLEY_SMI, etc js arrays.
So modern js engines are no more just an interpreter but also a list of runtime JIT compilers run depending of the context of the running code (the more a bit of code is run the more it uses the most complex JIT compiler with the most optimisation).
hence why js nowadays can be as fast as some compiled languages.
@14:59, is it not possible in this case to move the first element to the right and then update the base memory address to its moved location?
I've been wondering for some time now, what do you use to animate your videos?
4:30 I'm pretty sure it's APL that invented the bracket notation for array elements.
Please do streams would be so nice
what do you think about Fast LinkedList with algorithmic time complexity?
Hey Core Dumped, it would be so cool if you could make a vid on what object orientated programming is
Yes I want a stream!!!
May I give two thumbs up ?
Despite its quirks I love JavaScript for many reasons, one of which is that we want better performance in arrays, we can use typed arrays.
The hash map approach is quite clever IMO, since in most JS code you won't be looping more than a few hundred (or few thousand at the most) times in a normal array, and if you see doing more than that, then well, you should probably reconsider your approach.
All about being the right tool for the job. And if JS is just too slow, you've got WASM. And if WASM is too slow.......... then ditch JS/WASM and build a native app. 🤣
Yes I agree, the right tool for the right job. What I really dislike is that people trying to convince the world that JS should be used everywhere.
I love this guy, do you have a Patreon ?
how can I animate code?
and I don't mean by with just some random tool bcz I need to show off that I use vim
Let’s gooooo another video
Could someone kindly explain to me in depth and on a low-level 3:20? If ultimately all objects stored in memory (strings, ints, etc.) are just a sequence of bits at the end, how does the CPU differentiate (interpret) the binary sequence for the integer 65 and the binary sequence for the character "A"? Is there some "tag" that is associated with every variable that routes the variable to the correct processing unit within the CPU?
inherently all data that we use are indeed just a sequence of bits and bytes. the reason we have types in compiled systems languages is so that the compiler can use it to determine type information of something: the compiler can deduce the stack size, utilize packing for structs, ownership, etc. also reasoning about your code/instructions, from both the compiler and the programmer's perspective. you can think of types as a way to express something about the value associated to a name/symbol, i.e. "john" variable can contain a "Person" struct. you can also think of types as a property arising from restrictions/expectations of a data blob, i.e. think about a 7-bit character type that's actually allocated on a single byte.
ultimately, there's nothing inherently low-level preventing from eliminating all types and treating everything as a generic sequence of bytes. but that is counterintuitive for the compiler and the programmer.
edit: i implied this but to clarify, the processor doesn't know the type of a piece of data (well not exactly, but this is a good approximation for programmers). even instructions and pointers are data from the perspective of the processor.
also in interpreted languages, yes there are indeed tags attached to objects to keep track of the data they hold. i'm not aware if there's interpreted languages that doesn't use tags
Couldnt you use a map to access elements in a linked list, and making the lookup time constant with that?
I'm teaching web programming, actually javascript, I had same question, how the script languages handle unsized arrays, store memory, I meant dynamic arrays, thanks for explanation. btw performance is good enough.
the information presented here about js is wrong though.
js runtime have like 20 diffrenent representations of arrays internally to have dedicated optimisitations on them. for ex, array of number are internally represented like c arrays and are super performant
@@alfredomoreira6761 I learnt c++ and data structures, in c++ you do all(as you know), but in js you don't even tell the size, that seems little weird after c++, so I had to explain this procces. arrays are actually data type, not just data type , but complex abstraction for beginners.