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I had a similar thought a few years ago with an Advent of Code problem for which my solution in python might have been max(map(sum, input_list.split(None)))

I had a similar thought a few years ago with an Advent of Code problem for which my solution in python might have been max(map(sum, input_list.split(None))) To decipher this the eye has to jump to the middle of the line, move rightwards, then to the left to see the "map" then move right again to see what we are mapping and then all the way to the beginning to find the "max". The author would probably suggest rust's syntax* of values.iter().split(None).map(Iterator::sum).max().unwrap_or(0) but I was learning q at the time so came up with the much clearer /s, right to left max((0^+)\)l *: Though neither python nor rust have such a nice `.split(None)` built in.

papercrane 1y ago
> Though neither python nor rust have such a nice `.split(None)` built in. Sorry, I'm not sure I understand what `.split(None)` would do? My initial instinct is that would would return each character. i.e. `.chars()` in Rust or `list(s)` in Python.
- rspencer 1y ago
  It was intended to split a list of `int|None` into its non-none stretches. Much like how `string.split('x')` splits a string by matching the character 'x'
  - papercrane 1y ago
    Gotcha! In python there is a `split_at` function for this in the more-itertools package, but I don't think there is a concise way to do it in the stdlib.
- bear8642 1y ago
  >Sorry, I'm not sure I understand what `.split(None)` would do? Reading the docs [0] it seems `.split(None)` returns an array of the indivual characters without whitespace - so something like [c in list(s) if not whitespace(c)] [0] https://docs.python.org/3.3/library/stdtypes.html?highlight=split#str.split https://docs.python.org/3.3/library/stdtypes.html?highlight=...
layer8 1y ago
Honestly, I find using intermediate variables more readable than a long chain of function invocations where you have to keep track of intermediate results in your head: input_groups = input_list.split(None) group_sums = map(sum, input_groups) max_sum = max(group_sums) This also gives you a slightly higher-level view on how the algorithm proceeds just by reading the variable names on the LHS.
- matusp 1y ago
  The problem with this approach for me is that I don't know which variables are important outside of this snippet or outside of the next line. Is input_groups something I should keep in my head or is it just an intermediate result that can be discarded from my attention right away? The pipe-like solutions are nice because they are self-contained and you know that you only care about the final result and can abstract away the implementation. I prefer python comprehensions for the same reason. I can tell that they are about crating a list or a dict and I don't need to parse a bunch of operations in a loop to come to the same conclusion.
Philpax 1y ago
Rust doesn't have it built in, but it's part of itertools: https://docs.rs/itertools/latest/itertools/trait.Itertools.html#method.chunk_by https://docs.rs/itertools/latest/itertools/trait.Itertools.h... This may eventually be upstreamed: https://github.com/rust-itertools/itertools/issues/1026 https://github.com/rust-itertools/itertools/issues/1026
adregan 1y ago
Is the q solution equivalent? In doing a plus scan, isn't the last element always going to be the largest? To find the largest subarray sum, I would think you'd want to split into a matrix along the `null`s first and then plus reduction and then a max of those results. Say what you will about clarity, but my mind sort of glossed over the intention in the python and rust code, focusing instead on the syntax, while the q code made me consider what was actually happening.
- rspencer 1y ago
  It is equivalent because it's not a plus-scan but a (0^+)-scan which resets every time it hits a null (there's a more in depth explanation here https://robertandrewspencer.com/aoc_2022_1/ https://robertandrewspencer.com/aoc_2022_1/ ) Perhaps q did both force you to consider what was happening, and hide it from you...
  - adregan 1y ago
    Thanks! Though hopefully, once the idiom is learned, I'll be able to remember it :) Curious as to why a scan \ rather than a reduction /?

papercrane 1y ago

> Though neither python nor rust have such a nice `.split(None)` built in. Sorry, I'm not sure I understand what `.split(None)` would do? My initial instinct is that would would return each character. i.e. `.chars()` in Rust or `list(s)` in Python.

rspencer 1y ago
It was intended to split a list of `int|None` into its non-none stretches. Much like how `string.split('x')` splits a string by matching the character 'x'
- papercrane 1y ago
  Gotcha! In python there is a `split_at` function for this in the more-itertools package, but I don't think there is a concise way to do it in the stdlib.
bear8642 1y ago
>Sorry, I'm not sure I understand what `.split(None)` would do? Reading the docs [0] it seems `.split(None)` returns an array of the indivual characters without whitespace - so something like [c in list(s) if not whitespace(c)] [0] https://docs.python.org/3.3/library/stdtypes.html?highlight=split#str.split https://docs.python.org/3.3/library/stdtypes.html?highlight=...

layer8 1y ago

Honestly, I find using intermediate variables more readable than a long chain of function invocations where you have to keep track of intermediate results in your head: input_groups = input_list.split(None) group_sums = map(sum, input_groups) max_sum = max(group_sums) This also gives you a slightly higher-level view on how the algorithm proceeds just by reading the variable names on the LHS.

matusp 1y ago
The problem with this approach for me is that I don't know which variables are important outside of this snippet or outside of the next line. Is input_groups something I should keep in my head or is it just an intermediate result that can be discarded from my attention right away? The pipe-like solutions are nice because they are self-contained and you know that you only care about the final result and can abstract away the implementation. I prefer python comprehensions for the same reason. I can tell that they are about crating a list or a dict and I don't need to parse a bunch of operations in a loop to come to the same conclusion.

Philpax 1y ago

Rust doesn't have it built in, but it's part of itertools: https://docs.rs/itertools/latest/itertools/trait.Itertools.html#method.chunk_by https://docs.rs/itertools/latest/itertools/trait.Itertools.h... This may eventually be upstreamed: https://github.com/rust-itertools/itertools/issues/1026 https://github.com/rust-itertools/itertools/issues/1026

adregan 1y ago

Is the q solution equivalent? In doing a plus scan, isn't the last element always going to be the largest? To find the largest subarray sum, I would think you'd want to split into a matrix along the `null`s first and then plus reduction and then a max of those results. Say what you will about clarity, but my mind sort of glossed over the intention in the python and rust code, focusing instead on the syntax, while the q code made me consider what was actually happening.

rspencer 1y ago
It is equivalent because it's not a plus-scan but a (0^+)-scan which resets every time it hits a null (there's a more in depth explanation here https://robertandrewspencer.com/aoc_2022_1/ https://robertandrewspencer.com/aoc_2022_1/ ) Perhaps q did both force you to consider what was happening, and hide it from you...
- adregan 1y ago
  Thanks! Though hopefully, once the idiom is learned, I'll be able to remember it :) Curious as to why a scan \ rather than a reduction /?