Keiko Arai
@keikoa
Member · Member since Jun 2014
Python, numerics.
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- Spark: how to avoid a shuffle when joining a small table?
Broadcast the small side: from pyspark.sql.functions import broadcast facts.join(broadcast(lookup), "country_code") Spark also does this automatically below spa
Likes given · 10/12/2026
- Embedded C: volatile still needed for memory-mapped registers?
With modern compilers and -O2, is volatile still required for hardware registers, or are memory barriers enough?
Likes given · 10/12/2026
- Floating point: why is 0.1 + 0.2 != 0.3?
No — 0.1 and 0.2 have no exact binary representation, so the sum is 0.30000000000000004. Compare with a tolerance: Math.abs(a - b) < Number.EPSILON and use inte
Likes given · 10/12/2026
- Floating point: why is 0.1 + 0.2 != 0.3?
0.1 + 0.2 === 0.3 is false in JavaScript. Is the language broken?
Likes given · 10/12/2026
- Async Python: run blocking code without freezing the event loop
Push it to a thread: result = await asyncio.to_thread(blocking_fn, arg) For CPU-heavy work use a process pool with loop.run_in_executor(ProcessPoolExecutor(), f
Likes given · 10/12/2026
- Java: concurrent modification exception when removing from a list in a for-each loop
Use removeIf: names.removeIf(String::isBlank); or an explicit Iterator and it.remove().
Likes given · 10/12/2026
- Java: concurrent modification exception when removing from a list in a for-each loop
for (String s : names) { if (s.isBlank()) names.remove(s); } throws ConcurrentModificationException. How should I remove while iterating?
Likes given · 10/12/2026
- Kubernetes pod stuck in CrashLoopBackOff, no logs
--previous showed a missing env var. Thanks!
Likes given · 10/12/2026
- Kubernetes pod stuck in CrashLoopBackOff, no logs
Look at the previous container and the events: kubectl logs mypod --previous kubectl describe pod mypod # check Last State, Exit Code, Events Exit code 137 is
Likes given · 10/12/2026
- Python: what is the difference between __str__ and __repr__?
__repr__ is for developers: unambiguous, ideally valid Python that recreates the object. Used by the REPL, repr(), and containers. __str__ is for users: readabl
Likes given · 10/12/2026
- SQL: get the latest row per group
An index on (customer_id, created_at DESC) makes both of these fast.
Likes given · 10/12/2026
- SQL: get the latest row per group
In Postgres the shortest form is DISTINCT ON: SELECT DISTINCT ON (customer_id) * FROM orders ORDER BY customer_id, created_at DESC; Portable SQL uses a window f
Likes given · 10/12/2026
- SQL: get the latest row per group
For each customer_id I need the most recent order from orders(id, customer_id, created_at, total).
Likes given · 10/12/2026
- Regex to match a hex colour like #fff or #1a2b3c
/^#(?:[0-9a-f]{3}){1,2}$/i {1,2} allows exactly 3 or 6 hex digits. Add |[0-9a-f]{8} inside the group if you also want #rrggbbaa.
Likes given · 10/12/2026
- Go: all goroutines are asleep — deadlock! with an unbuffered channel
A send on an unbuffered channel blocks until another goroutine receives. main is the only goroutine, so it blocks on the send forever. Either receive in another
Likes given · 10/12/2026
- Go: all goroutines are asleep — deadlock! with an unbuffered channel
func main() { ch := make(chan int) ch <- 1 fmt.Println(<-ch) } Why does this deadlock?
Likes given · 10/12/2026
- Docker container exits immediately with code 0
FROM node:22-alpine WORKDIR /app COPY . . RUN npm ci CMD npm start & docker run returns right away and docker ps shows nothing. Logs are empty.
Likes given · 10/12/2026
- JavaScript: why does [1, 2, 10].sort() put 10 before 2?
[1, 2, 10].sort() // [1, 10, 2] Is this a bug?
Likes given · 10/12/2026
- Rust: "borrowed value does not live long enough" when returning a &str from a function
fn first_word(s: String) -> &str { s.split(' ').next().unwrap() } The compiler says the borrowed value does not live long enough. I just want the first word
Likes given · 10/12/2026