Ruby's hash is a Swiss-army knife • Hacker News Board

Re: Ruby's hash is a Swiss-army knife

#11

Post by ceautery » Mon, Aug 21, 2023, 12:08 AM UTC

my_new_account0 wrote: post #9

software_writer wrote: post #8

Earlier quoted context omitted.

Yes, hashes in Ruby, associative arrays in PHP, maps in Go[1], dictionaries in Python[2] and C#[3] represent the same concept, a collection of key-value pairs. [1]: https://gobyexample.com/maps [2]: https://docs.python.org/3/tutorial/datastructures.html#dicti... [3]: https://learn.microsoft.com/en-us/dotnet/api/system.collecti...

Yes. The OP's post is basically "baby's first API." The are a very handy API but relying on them at scale is much less efficient than structs or arrays. This post doesn't even go into the different performance characters of these APIs, which can be a major foot gun. I've noticed a lot of novice-level posts on here lately. Although I admit the post was very well written.

Novice level posts are great. Someone found something exciting to them, not new to us, but we should encourage them to keep exploring and writing.

Re: Ruby's hash is a Swiss-army knife

#12

Post by schrodinger » Mon, Aug 21, 2023, 12:30 AM UTC

ceautery wrote: post #11

my_new_account0 wrote: post #9

Earlier quoted context omitted.

Yes. The OP's post is basically "baby's first API." The are a very handy API but relying on them at scale is much less efficient than structs or arrays. This post doesn't even go into the different performance characters of these APIs, which can be a major foot gun. I've noticed a lot of novice-level posts on here lately. Although I admit the post was very well written.

Novice level posts are great. Someone found something exciting to them, not new to us, but we should encourage them to keep exploring and writing.

Also, the votes imply interest!

Re: Ruby's hash is a Swiss-army knife

#13

Post by crote » Mon, Aug 21, 2023, 12:48 AM UTC

software_writer wrote: post #8

drbojingle wrote: post #5

PHP's associative array is very similar yea?

Yes, hashes in Ruby, associative arrays in PHP, maps in Go[1], dictionaries in Python[2] and C#[3] represent the same concept, a collection of key-value pairs. [1]: https://gobyexample.com/maps [2]: https://docs.python.org/3/tutorial/datastructures.html#dicti... [3]: https://learn.microsoft.com/en-us/dotnet/api/system.collecti...

The interesting thing is that it definitely feels different to me.

While the basic data structure is obviously identical to its counterparts, the way it interacts with the ecosystem as a whole makes it feel way more powerful. The interaction of hashes, symbols, and blocks lead to a language which feels like it is designed with DSLs as first-class citizens. This leads to things like Ruby on Rails, which at first glance feels like pure magic.

I get a somewhat similar feeling about lists in Python. Because of its very extensive list comprehension you start thinking in lists, leading to some very clean code which would be extremely awkward to implement in many other languages.

Re: Ruby's hash is a Swiss-army knife

#14

Post by sottol » Mon, Aug 21, 2023, 1:06 AM UTC

In my opinion Lua's equivalent tables or more of a Swiss army knife.

It's been a while since I've used them but afair they combine hash/dict, array and objects in one data structure.

They're hashes as usual. With a special constructor or int keys they turn into arrays, last I looked the Lua interpreter even optimizes contiguous ranges of keys as arrays. And by adding metatables and metamethods they also emulate JS-style objects.

Re: Ruby's hash is a Swiss-army knife

#15

Post by q7xvh97o2pDhNrh » Mon, Aug 21, 2023, 1:12 AM UTC

This is a lovely overview. Hash is a great example of how delightful it can be to program in Ruby.

One more technique worth noting is the chained functional style of using Hash, which you can do in Ruby because Hash inherits from Enumerable. If you're prototyping a script to do some data-cleaning, this makes it easy to build up your pipeline and iterate on it. For example:

    foobar = { ...your data here... }
    foobar.map do |k, v|
      # ...
      # do some transformation here
      # ...
      # and then return the replacement key/value for this entry
      [key, new_value]
    end.select do |k, v|
      # do some filtering here, e.g.:
      is_foobarable?(k, v)
    end.map do |k, v|
      # ...
      # do some expensive transformation here on the smaller data set
      # ...
      [key, newer_value]
    end.to_h

(Note that you have to call #to_h at the end since the Enumerable functions will coerce the hash into an array of arrays.)

Now your code literally shows the pipeline that your data is falling through — and each of these steps can be side-effect-free, with no mutations to the original foobar structure.

Re: Ruby's hash is a Swiss-army knife

#16

Post by Gigachad » Mon, Aug 21, 2023, 1:34 AM UTC

block_dagger wrote: post #2

Ruby’s Hash is probably the handiest data structure I’ve ever encountered. Thanks Matz.

I wish it was typed though. So many times I’ve seen a function that takes a hash of “options” or “config” and have no idea what that actually contains. Even for official rails methods it’s often complex to know what the possible options are. Some of them seem almost internal with how obscure they are.

Re: Ruby's hash is a Swiss-army knife

#17

Post by my_new_account0 » Mon, Aug 21, 2023, 1:45 AM UTC

q7xvh97o2pDhNrh wrote: post #15

This is a lovely overview. Hash is a great example of how delightful it can be to program in Ruby. One more technique worth noting is the chained functional style of using Hash, which you can do in Ruby because Hash inherits from Enumerable. If you're prototyping a script to do some data-cleaning, this makes it easy to build up your pipeline and iterate on it. For example: foobar = { ...your data here... } foobar.map…

Unless things have changed and Ruby has stream fusion now, this is bad advice for scale. You are iterating over a fat object multiple times. Even if its uglier its much better in this case to create an empty array/hash, iterate over with #each and #I worked at the largest Rails shop in the world and this would be rejected in code review.

Edited to add more detail: the only method you need to write to implement Enumerable is #each. Every step of your pipeline here is _another_ call to #each. Just do it once.

Re: Ruby's hash is a Swiss-army knife

#18

Post by dikei » Mon, Aug 21, 2023, 1:55 AM UTC

my_new_account0 wrote: post #9

software_writer wrote: post #8

Earlier quoted context omitted.

Yes, hashes in Ruby, associative arrays in PHP, maps in Go[1], dictionaries in Python[2] and C#[3] represent the same concept, a collection of key-value pairs. [1]: https://gobyexample.com/maps [2]: https://docs.python.org/3/tutorial/datastructures.html#dicti... [3]: https://learn.microsoft.com/en-us/dotnet/api/system.collecti...

Yes. The OP's post is basically "baby's first API." The are a very handy API but relying on them at scale is much less efficient than structs or arrays. This post doesn't even go into the different performance characters of these APIs, which can be a major foot gun. I've noticed a lot of novice-level posts on here lately. Although I admit the post was very well written.

I find it funny that he said he didn't know what to pick between 5 types of IDictionary in C#.

* Hashtable

* SortedList

* Dictionary

* ConcurrentDictionary

I don't even know C# (just Java), yet I know that you'd probably want to use Dictionary most of the time.

Re: Ruby's hash is a Swiss-army knife

#19

Post by faitswulff » Mon, Aug 21, 2023, 2:13 AM UTC

My favorite little-known fact about Ruby hashes is that they respond to `to_proc` and can be used as procs. For example, you can do this:

a = { 1 => 'a', 2 => 'b' }

[1, 2, 3].map(&a)

#=> ['a', 'b', nil]

Re: Ruby's hash is a Swiss-army knife

#20

Post by djur » Mon, Aug 21, 2023, 2:23 AM UTC

my_new_account0 wrote: post #9

software_writer wrote: post #8

Earlier quoted context omitted.

Yes, hashes in Ruby, associative arrays in PHP, maps in Go[1], dictionaries in Python[2] and C#[3] represent the same concept, a collection of key-value pairs. [1]: https://gobyexample.com/maps [2]: https://docs.python.org/3/tutorial/datastructures.html#dicti... [3]: https://learn.microsoft.com/en-us/dotnet/api/system.collecti...

Yes. The OP's post is basically "baby's first API." The are a very handy API but relying on them at scale is much less efficient than structs or arrays. This post doesn't even go into the different performance characters of these APIs, which can be a major foot gun. I've noticed a lot of novice-level posts on here lately. Although I admit the post was very well written.

My experience is that Struct only performs better than Hash in a pretty narrow set of circumstances, rarely enough to be a deciding factor unless profiling suggests it to be.