Is it possible to sort a dictionary in Julia? - sorting

Question

I have created a dictionary out of two arrays using zip() like
list1 = [1,2,3,4,5]
list2 = [6,7,8,9,19]
dictionary1 = Dict(zip(list1,list2))
Now i want to sort this dictionary by key(list1) or by list2. Can somebody show me a way or function, how to realize it?

Answer 1

Sort also takes a by keyword, which means you can do:
julia> sort(collect(dictionary1), by=x->x[2])
5-element Array{Tuple{Int64,Int64},1}:
(1,6)
(2,7)
(3,8)
(4,9)
(5,19)
Also note that there is a SortedDict in DataStructures.jl, which maintains sort order, and there's an OrderedDict which maintains insertion order. Finally, there's a pull request which would allow direct sorting of OrderedDicts (but I need to finish it up and commit it).

Answer 2

While SortedDict may be useful if it is necessary to keep the dictionary sorted, it is often only necessary to sort the dictionary for output, in which case, the following may be what is required:
list1 = [1,2,3,4,5]
list2 = [6,7,8,9,19]
dictionary1 = Dict(zip(list1,list2))
sort(collect(dictionary1))
... which produces:
5-element Array{(Int64,Int64),1}:
(1,6)
(2,7)
(3,8)
(4,9)
(5,19)
We can sort by values with:
sort(collect(zip(values(dictionary1),keys(dictionary1))))
... which gives:
5-element Array{(Int64,Int64),1}:
(6,1)
(7,2)
(8,3)
(9,4)
(19,5)

Answer 3

The byvalue keyword for the sort function (or sort! for mutating/in place sorting) is useful for sorting dictionaries in order of their values (as opposed to their keys). The result will be of type OrderedDict from OrderedCollections.jl (it's also re-exported by DataStructures.jl).
list1 = [2,1,3,4,5]
list2 = [9,10,8,7,6]
dictionary1 = Dict(zip(list1,list2))
Sort by value (i.e. by list2):
sort(dictionary1; byvalue=true)
Output:
OrderedDict{Int64, Int64} with 5 entries:
5 => 6
4 => 7
3 => 8
2 => 9
1 => 10
Sort by key (i.e. by list1):
sort(dictionary1)
Output:
OrderedDict{Int64, Int64} with 5 entries:
1 => 10
2 => 9
3 => 8
4 => 7
5 => 6