Sort keys of NamedTuple

General Usage
,
1

I would like to sort a NamedTuple alphabetically by its keys. For instance:

(b=1, a=2, c=3) ---> (a=2, b=1, c=3)
(a=1, c=2, b=3) ---> (a=1, b=3, c=2)

I am pretty sure such functionality already exists, where to look for it? Bonus points if the solutions infers.

2

Not sure if this is reasonable:

using TupleTools
nt = (b=1, a=2, c=3)
NamedTuple{TupleTools.sort(keys(nt))}(nt)
# result:
(a = 2, b = 1, c = 3)
3 Likes
3

Dependency-free, infers, compiles to basically a no-op:

@generated sortkeys(nt::NamedTuple{KS}) where {KS} =
    :( NamedTuple{$(Tuple(sort(collect(KS))))}(nt) )
6 Likes
4

could you please explain how it works in some detail?
For example, where does it happen that in addition to sorting the keys the values are also correspondingly sorted?

5

Both of those solutions work in the same manner.

julia> nt = (b=1, a=2, c=3)
(b = 1, a = 2, c = 3)

julia> typeof(nt)
NamedTuple{(:b, :a, :c), Tuple{Int64, Int64, Int64}}

julia> NamedTuple{(:a,:b,:c)}(nt)
(a = 2, b = 1, c = 3)

The last line works because of (from ? NamedTuple)

NamedTuple{names}(nt::NamedTuple)

  Construct a named tuple by selecting fields in names (a tuple of Symbols) from another named tuple.
1 Like
6

Very interesting.
Now I can understand at least part of @aplavin solution
Seems to work for some of the fields as well.

 NamedTuple{(:c,:b)}(nt)