Map.invert is at least largely harmless, unlike some of the other proposals
that happen. It's still a little odd to me to have a function that boils
down to just:
Map.new(map, fn {k, v} -> {v, k} end)
Honestly that is almost clearer if you've never heard the word "invert"
with respect to maps.
On Wednesday, February 6, 2019 at 1:35:49 AM UTC-5, Justin Gamble wrote:
>
> Hi,
>
> I think an invert() method on Map would be convenient to use. It is only
> a handful of lines of code to add to a custom program, but why should users
> need to do that? In my opinion this basic functionality should be
> implemented by the Map module.
>
> The invert() method would operate the same way it does for Ruby:
> https://ruby-doc.org/core-2.2.2/Hash.html#method-i-invert
>
> Recently I wanted to invert a map in one of my Elixir programs (details
> below), and I googled and found the below solution by Chris McCord in h
> ttps://stackoverflow.com/questions/26614682/how-to-change-all-the-values-in-an-elixir-map
> :
>
> def invert(map) when is_map(map) do
> for {k, v} <- map, into: %{}, do: {v, k}
> end
>
> I would basically like the above function to be added to the Elixir.Map
> module.
>
> Here is the scenario for which I wanted to use this the invert function:
>
> *My Elixir program is synchronizing Robot Framework source code files with
> TestRail. Robot Framework defines automated test cases. TestRail is a
> web-based Test Case Management system. The goal is to synchronize
> TestRail to contain all the tests that are defined in the Robot Framework
> files, and in the same directory structure.*
>
> *Originally the Elixir program was specified to only create test cases in
> TestRail. When you are creating a test case, the TestRail API
> <http://docs.gurock.com/testrail-api2/reference-cases#add_case> requires
> you to specify the ID of the directory (aka "section") where the case is
> written. For this I use an Elixir Map to map paths to section IDs. When I
> want to create a file in directory "/path/to/test.robot", then I Lookup the
> section ID from my map & then call the "add_case" TestRail API function.*
>
> *That version of the program was a success. My boss was impressed and
> next asked for enhancements to the program. The new functionality being
> requested is to have existing TestRail Test Cases get updated with the
> latest test steps defined in Robot Framework. Part of that update is to
> verify that the path to the test case is the same in the Robot Framework
> source code and in the TestRail. In this case we first call the TestRail
> API to lookup a test case, at which point we know the section ID that it
> belongs to. But we need to translate that to a directory path and confirm
> that this path is the same location as where the test file exists in the
> Robot Framework source code. *
>
> *For updating, it makes sense to also be able to use an Elixir Map to map
> from the Section ID back to the Path -- the inverse of the original map. *
>
> *It is true that I could iterate through the original map until I found
> the section ID in the value section, and then return the map index. But
> that seems awfully inefficient when you consider that there are hundreds of
> test files and thousands of tests. So I decided an inverse map would
> provide faster lookup, at the cost of more memory being used. Also note
> that in my scenario both the indexes and the values are unique; it is a
> 1-to-1 mapping.*
>
>
> This is just one example scenario. I imagine other examples exist, or
> else the invert() function would never have been created in the Ruby
> community.
>
>
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