OrderedDict with duplicate items?

[Ahmed_Salih]

Hello!

Would anyone know if it is possible to make a slight rewrite, such that one can make a dict with duplicate entries in a specific order, initially set?

I see from this answer that one can make a duplicate key dict by using Base.ImmutableDict

Initialising a dictionary with duplicate keys

If you, for some reason, want to have dictionary with duplicate keys you can use Base.ImmutableDict (which is however a bit tricky to use): julia> a = Base.ImmutableDict(Base.ImmutableDict(Pair(:x, 1)), Pair(:x, 2)) Base.ImmutableDict{Symbol,Int64} with 2 entries: :x => 2 :x => 1 Note that adding a new value with the same key will override the initial definition, so julia> a[:x] 2

But I also want to enforce a specific ordering.

Kind regards

[mastrof]

Just out of curiosity, why do you want such a data structure?

I’m a Julia newbie, so 99.9% there are better ways to achieve what you want, but if I had to do something like that I would go with a vector of Pairs rather than an Ordered dict with duplicates, maybe something like this:

data = [Pair(:field1, 1), Pair(:field2, 2), Pair(:field1, 3)]
f(vec, field) = [x.second for x in vec if x.first==field]

Then f(data, :field1) returns [1, 3].

[Ahmed_Salih]

Hi!

It sounds very “weird” to do so I agree, the only reason for this is that I am using dicts in connection with LightXML to construct XML files. These files do not care about this when processed by a macine (it just finds the relevant tags), but since I want it to be human readable as well a specific ordering is of preference.

Thanks for your curiosity. I think using a vector of pairs rather than a dict could be a potential rewrite in the future, thanks for bringing it to my attention!

Kind regards

[benninkrs]

The DataStructures package has quite a few different types of Dicts, including sorted Multi dicts. But it’s not clear to me what kind of order you are looking for.

[Ahmed_Salih]

Hi!

I want this order:

By using immutable dict I get this:

So I want “SavePosDouble” to be at the top, instead of the bottom in this picture.

If I could do it with an “OrderedDict” it would be nice, but if you know any ways involving dicts which allows me to force an order and duplicate tags i.e. “parameter”, I would love to hear more

Kind regards

[benninkrs]

Ok, I understand that you want the keys in given order. But there are no duplicate keys (that is, keys with multiple values) in your example. I am not aware of a dict that both allows duplicated keys and maintains insertion order. But it’s not clear what that means. What if you add a key at the beginning, then add the same key again later? Where should it go? Should it go at the end or be merged with the first entry?

[Ahmed_Salih]

Okay I am using Dict inside of Julia. Using the base version:

Dict("a"=>1,"a"=>2)
Dict{String,Int64} with 1 entry:
  "a" => 2

Since I have a duplicate key “a”, I only get 1 entry. Using then:

Base.ImmutableDict("a"=>1,"a"=>2)
Base.ImmutableDict{String,Int64} with 2 entries:
  "a" => 2
  "a" => 1

It now gives me both entries but not in the order I specified. Using finally:

OrderedDict("a"=>1,"a"=>2)
OrderedDict{String,Int64} with 1 entry:
  "a" => 2

Same issue as with the first approach. I want it to return to me a dict with two entries, where “a” => 1 is first, then “a” => 2.

EDIT: Adding a key later is not possible as of now in what I want to implement. Everything is generated from scratch each time and not altered afterwards.

Kind regards

[benninkrs]

Usually dicts are used when you want fast random access with arbitrary keys. It sounds like you’re just going to iterate over the keys and values, so as suggested above a simple array of key/value pairs might be more appropriate.

[Ahmed_Salih]

I see. Will look into this when doing a rewrite later.

Kind regards