iter | Iteration primitives using generators | Functional Programming library
kandi X-RAY | iter Summary
kandi X-RAY | iter Summary
This library implements iteration primitives like map() and filter() using generators. To a large part this serves as a repository for small examples of generator usage, but of course the functions are also practically quite useful. All functions in this library accept arbitrary iterables, i.e. arrays, traversables, iterators and aggregates, which makes it quite different from functions like array_map() (which only accept arrays) and the SPL iterators (which usually only accept iterators, not even aggregates). The operations are of course lazy.
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QUESTION
I have been trying to learn about functional programming, but I still struggle with thinking like a functional programmer. One such hangup is how one would implement index-heavy operations which rely strongly on loops/order-of-execution.
For example, consider the following Java code:
...ANSWER
Answered 2022-Mar-07 at 21:17This is not an index-heavy operation, in fact you can do this with a one-liner with scanl1 :: (a -> a -> a) -> [a] -> [a]:
QUESTION
I'm trying to initiate a Springboot project using Open Jdk 15, Springboot 2.6.0, Springfox 3. We are working on a project that replaced Netty as the webserver and used Jetty instead because we do not need a non-blocking environment.
In the code we depend primarily on Reactor API (Flux, Mono), so we can not remove org.springframework.boot:spring-boot-starter-webflux dependencies.
I replicated the problem that we have in a new project.: https://github.com/jvacaq/spring-fox.
I figured out that these lines in our build.gradle file are the origin of the problem.
...ANSWER
Answered 2022-Feb-08 at 12:36This problem's caused by a bug in Springfox. It's making an assumption about how Spring MVC is set up that doesn't always hold true. Specifically, it's assuming that MVC's path matching will use the Ant-based path matcher and not the PathPattern-based matcher. PathPattern-based matching has been an option for some time now and is the default as of Spring Boot 2.6.
As described in Spring Boot 2.6's release notes, you can restore the configuration that Springfox assumes will be used by setting spring.mvc.pathmatch.matching-strategy to ant-path-matcher in your application.properties file. Note that this will only work if you are not using Spring Boot's Actuator. The Actuator always uses PathPattern-based parsing, irrespective of the configured matching-strategy. A change to Springfox will be required if you want to use it with the Actuator in Spring Boot 2.6 and later.
QUESTION
I'd like to provide a view for a customer data structure, with it's own iterator. I wrote a small program to test it out, shown below. It I uncomment begin(), then it works. But if I use DummyIter, then I get a compile error.
In my full program, I've implemented a full iterator but for simplicity, I narrowed it down to the necessary functions here.
...ANSWER
Answered 2022-Mar-18 at 11:01This can't work since return types of your begin and end do not match.
So basically those iterators can't be compared to each other.
Prove:
- here is your code with extra static assert
- here is dummy fix which compiles since now same return type is used for
beginandend
Minimum requirement is that result of begin() and end() are comparable. Different types for begin() and end() are useful when size of range is not known. Here is nice explanation of sentinel (mentioned in comment).
QUESTION
In the current stable Rust, is there a way to write a function equivalent to BTreeMap::pop_last?
The best I could come up with is:
...ANSWER
Answered 2022-Mar-15 at 16:55Is there a way to work around this issue without imposing additional constraints on map key and value types?
It doesn't appear doable in safe Rust, at least not with reasonable algorithmic complexity. (See Aiden4's answer for a solution that does it by re-building the whole map.)
But if you're allowed to use unsafe, and if you're determined enough that you want to delve into it, this code could do it:
QUESTION
I have an array of positive integers. For example:
...ANSWER
Answered 2022-Feb-27 at 22:44This problem has a fun O(n) solution.
If you draw a graph of cumulative sum vs index, then:
The average value in the subarray between any two indexes is the slope of the line between those points on the graph.
The first highest-average-prefix will end at the point that makes the highest angle from 0. The next highest-average-prefix must then have a smaller average, and it will end at the point that makes the highest angle from the first ending. Continuing to the end of the array, we find that...
These segments of highest average are exactly the segments in the upper convex hull of the cumulative sum graph.
Find these segments using the monotone chain algorithm. Since the points are already sorted, it takes O(n) time.
QUESTION
I was using pyspark on AWS EMR (4 r5.xlarge as 4 workers, each has one executor and 4 cores), and I got AttributeError: Can't get attribute 'new_block' on . Below is a snippet of the code that threw this error:
...ANSWER
Answered 2021-Aug-26 at 14:53I had the same error using pandas 1.3.2 in the server while 1.2 in my client. Downgrading pandas to 1.2 solved the problem.
QUESTION
Springfox 3.0.0 is not working with Spring Boot 2.6.0, after upgrading I am getting the following error
...ANSWER
Answered 2021-Dec-01 at 02:17I know this does not solve your problem directly, but consider moving to springdoc which most recent release supports Spring Boot 2.6.0. Springfox is so buggy at this point that is a pain to use. I've moved to springdoc 2 years ago because of its Spring WebFlux support and I am very happy about it. Additionally, it also supports Kotlin Coroutines, which I am not sure Springfox does.
If you decide to migrate, springdoc even has a migration guide.
QUESTION
I am reading this book by Fedor Pikus and he has some very very interesting examples which for me were a surprise.
Particularly this benchmark caught me, where the only difference is that in one of them we use || in if and in another we use |.
ANSWER
Answered 2022-Feb-08 at 19:57Code readability, short-circuiting and it is not guaranteed that Ord will always outperform a || operand.
Computer systems are more complicated than expected, even though they are man-made.
There was a case where a for loop with a much more complicated condition ran faster on an IBM. The CPU didn't cool and thus instructions were executed faster, that was a possible reason. What I am trying to say, focus on other areas to improve code than fighting small-cases which will differ depending on the CPU and the boolean evaluation (compiler optimizations).
QUESTION
I made a bubble sort implementation in C, and was testing its performance when I noticed that the -O3 flag made it run even slower than no flags at all! Meanwhile -O2 was making it run a lot faster as expected.
Without optimisations:
...ANSWER
Answered 2021-Oct-27 at 19:53It looks like GCC's naïveté about store-forwarding stalls is hurting its auto-vectorization strategy here. See also Store forwarding by example for some practical benchmarks on Intel with hardware performance counters, and What are the costs of failed store-to-load forwarding on x86? Also Agner Fog's x86 optimization guides.
(gcc -O3 enables -ftree-vectorize and a few other options not included by -O2, e.g. if-conversion to branchless cmov, which is another way -O3 can hurt with data patterns GCC didn't expect. By comparison, Clang enables auto-vectorization even at -O2, although some of its optimizations are still only on at -O3.)
It's doing 64-bit loads (and branching to store or not) on pairs of ints. This means, if we swapped the last iteration, this load comes half from that store, half from fresh memory, so we get a store-forwarding stall after every swap. But bubble sort often has long chains of swapping every iteration as an element bubbles far, so this is really bad.
(Bubble sort is bad in general, especially if implemented naively without keeping the previous iteration's second element around in a register. It can be interesting to analyze the asm details of exactly why it sucks, so it is fair enough for wanting to try.)
Anyway, this is pretty clearly an anti-optimization you should report on GCC Bugzilla with the "missed-optimization" keyword. Scalar loads are cheap, and store-forwarding stalls are costly. (Can modern x86 implementations store-forward from more than one prior store? no, nor can microarchitectures other than in-order Atom efficiently load when it partially overlaps with one previous store, and partially from data that has to come from the L1d cache.)
Even better would be to keep buf[x+1] in a register and use it as buf[x] in the next iteration, avoiding a store and load. (Like good hand-written asm bubble sort examples, a few of which exist on Stack Overflow.)
If it wasn't for the store-forwarding stalls (which AFAIK GCC doesn't know about in its cost model), this strategy might be about break-even. SSE 4.1 for a branchless pmind / pmaxd comparator might be interesting, but that would mean always storing and the C source doesn't do that.
If this strategy of double-width load had any merit, it would be better implemented with pure integer on a 64-bit machine like x86-64, where you can operate on just the low 32 bits with garbage (or valuable data) in the upper half. E.g.,
QUESTION
In my Fedora 34 environment (g++), std::accumulate is defined as:
ANSWER
Answered 2022-Jan-01 at 20:50The value category of init + *first doesn't matter.
init in init + *first is a lvalue.
So if init + *first calls an operator+ overload taking the parameter by-value, it will cause a copy construction of that parameter
But the value of init is not required anymore after init + *first, so it makes sense to move it into the parameter instead.
Similarly a operator+ overload taking its first argument by rvalue-reference might be used to allow modification of the argument by the operation.
This is what std::move achieves here.
The standard specifies this behavior since C++20.
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