Optimize groupBy using sofs

[bjorng]

On my computer, this optimization made it run 10 times faster.

[andreaferretti]

Just to be sure - I received the Erlang example, so I am not able to judge. The examples in other languages all use a groupBy operation, which in turn is usually implemented with a hashmap. Is this approach in Erlang equivalent?

[bjorng]

sofs does not use a hash map. It works by sorting the
list and then goes through the sorted list and groups
the values.

The rules says "idiomatic code", so I wrote idiomatic
code.

On Tue, Feb 24, 2015 at 10:55 AM, andreaferretti notifications@github.com
wrote:

Just to be sure - I received the Erlang example, so I am not able to
judge. The examples in other languages all use a groupBy operation, which
in turn is usually implemented with a hashmap. Is this approach in Erlang
equivalent?

—
Reply to this email directly or view it on GitHub
#12 (comment).

Björn Gustavsson, Erlang/OTP, Ericsson AB

[andreaferretti]

Unfortunately, this makes hard to compare the results with other languages. Would it be possible to provide a hashmap-based implementation?

[jlouis]

In general, no. Hashmaps in the traditional sense can't be implemented in a functional language because of data persistence. You can fake hashmaps pretty well through HAMT structures, but you won't get the same speed as a system which is able to do destructive updates. Once you begin looking at idiomatic Haskell or OCaml, chances are this will bite you as well.

[andreaferretti]

Well, HashMaps certainly do no need to be mutable. Scala has immutable, persistent hashmaps, and I think both OCaml and Haskell have them (but I am not sure).

[jlouis]

Both OCaml and Haskell have hashmap implementations, but you run into the trouble of what idiomatic means.

[andreaferretti]

I settled accepting the other pull request which follows more closely what is done in other languages