Parsing XML key/value pairs with \"key\":"\value\" synyax

Questions / Help
,
1

I am new to Elixir, but love what I am seeing so far! I would think Elixir would be a great suit for my query below given the pattern matching capabilities, but at my current level I am stuck.

My issue is as follows: I am trying to parse a list of key:value pairs from an XML file. I have included the first couple of pairs below.

["\"ClassNotationDocumentUrl\":\"\",\"VesselId\":\"40775\",\"IMONo\":\"9866718\",\"Currentname\":\"LOWLANDS CRIMSON\",\"VesselGuid\":\"a5379088-2c7d-42d8-bdf5-c5677ce5c1d2\",

I am struggling to figure out how to parse this into an Elixir struct, could anyone point me in the right direction?

Many thanks for your help!

2

This is one approach to get started; see below for notes about why it’s brittle:

iex(20)> Regex.scan(~r/"([^"]*)":"([^"]*)",?/, s, capture: :all_but_first)
[
  ["ClassNotationDocumentUrl", ""],
  ["VesselId", "40775"],
  ["IMONo", "9866718"],
  ["Currentname", "LOWLANDS CRIMSON"],
  ["VesselGuid", "a5379088-2c7d-42d8-bdf5-c5677ce5c1d2"]
]

The brittleness of this solution is from subexpressions like [^"]* - if the data ever contains " characters as part of a value this parser will break, as it doesn’t implement any kind of escaping.

2 Likes
3

I usually do something like this:

Enum.reduce(input_list, %{}, fn item, acc ->
  [key, value] =
    item
    |> String.replace("\"", "")
    |> String.split(":")

  Map.put(acc, key, value)
end)

For each item in the list, get rid of the quotation marks, split at the colon, and then put them into a map (or struct if the keys are always the same). Note how Elixir’s pattern matching allows us to easily assign key and value variables from the result of the pipeline.

2 Likes
4

Can’t provide a good example right now on phone but look at nimbleparsec package on hex. It’s brilliant for parsing all sorts of input.

3 Likes
5

Many thanks for quick responses - Super helpful!
I ended up going with the regex as it does the job well enough for my purpose.