sprite2005

sprite2005

Concurrent Data Processing in Elixir: Using a mapper operation after reduce/3 is deprecated (page 114)

@svilen

warning: Using a mapper operation, such as map/filter/reject, after reduce/3 is deprecated. Use Flow.on_trigger/2 instead
(flow 1.2.0) lib/flow.ex:1916: Flow.add_mapper/3
(airports 0.1.0) lib/airports.ex:25: Airports.open_airports/0
(stdlib 4.0.1) erl_eval.erl:744: :erl_eval.do_apply/7
(elixir 1.13.4) src/elixir.erl:296: :elixir.recur_eval/3
(elixir 1.13.4) src/elixir.erl:274: :elixir.eval_forms/3
(iex 1.13.4) lib/iex/evaluator.ex:310: IEx.Evaluator.handle_eval/3

How would we rewrite this as an on_trigger function?

Most Liked

andybab

andybab

This should work, but is longer than Flow.map version from book:

...
     |> Flow.reject(&(&1.type == "closed"))
     |> Flow.partition(key: {:key, :country})
     |> Flow.group_by(& &1.country)
     |> Flow.on_trigger(fn map ->
        country_data = Enum.map(map, fn {country, data} -> {country, Enum.count(data)} end)
        {country_data, map}
      end)
     #|> Flow.map(fn {country, data} -> {country, Enum.count(data)} end)
     |> Enum.to_list()
rschenk

rschenk

@svilen

I ran into this problem as well. While @andybab’s solution will produce the correct answer, I believe the use of Enum.map means that this part of the computation will not be calculated concurrently, whereas (I think?) the version in the book which uses Flow.map will be run in parallel. I could be wrong, I’m totally new at this.

It sure would be nice if the author of the book could provide a version that is both concurrent and not deprecated.

Edit: looks like my thinking was wrong. If you throw an IO.inspect(self()) into the andybab’s on_trigger callback, you can see that this does get split in parallel across multiple stages. For a noob, it’s confusing why/how this works and why you can’t use Flow.map instead, hopefully the author can update this section with an explanation.

Where Next?

Popular Pragmatic Bookshelf topics Top

jeffmcompsci
Title: Design and Build Great Web APIs - typo “https://company-atk.herokuapp.com/2258ie4t68jv” (page 19, third bullet in URL list) Typo:...
New
GilWright
Working through the steps (checking that the Info,plist matches exactly), run the demo game and what appears is grey but does not fill th...
New
joepstender
The generated iex result below should list products instead of product for the metadata. (page 67) iex> product = %Product{} %Pento....
New
brian-m-ops
#book-python-testing-with-pytest-second-edition Hi. Thanks for writing the book. I am just learning so this might just of been an issue ...
New
digitalbias
Title: Build a Weather Station with Elixir and Nerves: Problem connecting to Postgres with Grafana on (page 64) If you follow the defau...
New
brunogirin
When installing Cards as an editable package, I get the following error: ERROR: File “setup.py” not found. Directory cannot be installe...
New
kolossal
Hi, I need some help, I’m new to rust and was learning through your book. but I got stuck at the last stage of distribution. Whenever I t...
New
ggerico
I got this error when executing the plot files on macOS Ventura 13.0.1 with Python 3.10.8 and matplotlib 3.6.1: programming_ML/code/03_...
New
bjnord
Hello @herbert ! Trying to get the very first “Hello, Bracket Terminal!" example to run (p. 53). I develop on an Amazon EC2 instance runn...
New
redconfetti
Docker-Machine became part of the Docker Toolbox, which was deprecated in 2020, long after Docker Desktop supported Docker Engine nativel...
New

Other popular topics Top

AstonJ
If it’s a mechanical keyboard, which switches do you have? Would you recommend it? Why? What will your next keyboard be? Pics always w...
New
PragmaticBookshelf
Design and develop sophisticated 2D games that are as much fun to make as they are to play. From particle effects and pathfinding to soci...
New
AstonJ
You might be thinking we should just ask who’s not using VSCode :joy: however there are some new additions in the space that might give V...
New
dimitarvp
Small essay with thoughts on macOS vs. Linux: I know @Exadra37 is just waiting around the corner to scream at me “I TOLD YOU SO!!!” but I...
New
AstonJ
Saw this on TikTok of all places! :lol: Anyone heard of them before? Lite:
New
New
First poster: joeb
The File System Access API with Origin Private File System. WebKit supports new API that makes it possible for web apps to create, open,...
New
husaindevelop
Inside our android webview app, we are trying to paste the copied content from another app eg (notes) using navigator.clipboard.readtext ...
New
PragmaticBookshelf
Programming Ruby is the most complete book on Ruby, covering both the language itself and the standard library as well as commonly used t...
New
RobertRichards
Hair Salon Games for Girls Fun Girls Hair Saloon game is mainly developed for kids. This game allows users to select virtual avatars to ...
New

Sub Categories: