I was trying to merge multi-layered Dict which is…
x = [
Dict("d1"=>"A1")
Dict("d1b"=>Dict("d2a"=>"B1"))
Dict("d1b"=>Dict("d2b"=>"C1"))]
julia>merge(x...)
Dict{String,Any} with 2 entries:
"d1" => "A1"
"d1b" => Dict("d2b"=>"C1")
the second layer of a dictionary is being overwritten, so I could do this
julia>merge(merge, x...)
Dict{String,Any} with 2 entries:
"d1" => "A1"
"d1b" => Dict("d2b"=>"C1","d2a"=>"B1")
And I wanted to merge the third and fourth layer of a dictionary as well.
but merge(merge, x...) wouldn’t work here.
x = [ Dict("d1"=>"A1")
Dict("d1b"=>Dict("d2a"=>"B1"))
Dict("d1b"=>Dict("d2b"=>"C1"))
Dict("d1b"=>Dict("d2c"=>Dict("d3a"=>"D1")))
Dict("d1b"=>Dict("d2c"=>Dict("d3b"=>"E1")))]
julia> merge(merge, x...)
Dict{String,Any} with 2 entries:
"d1" => "A1"
"d1b" => Dict{String,Any}("d2b"=>"C1","d2a"=>"B1","d2c"=>Dict("d3b"=>"E1"))
third layer "d2c"=>Dict("d3a"=>"D1") are being overwritten here
It would be nice if I could accomplish this while preserving beautiful julia syntax 
How about
recursive_merge(x::AbstractDict...) = merge(recursive_merge, x...)
julia> recursive_merge(x...) # with your last x
Dict{String,Any} with 2 entries:
"d1" => "A1"
"d1b" => Dict{String,Any}("d2b"=>"C1","d2a"=>"B1","d2c"=>Dict("d3b"=>"E1","d3a"=>"D1"))
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I’m on mobile, so I’m not going to write it out, but I think your best bet might be some sort of recursive function with a loop or two. You can loop through keys with for k in keys (mydict), and check if a dictionary has a key with haskey(mydict, key).
Edit: oops, someone beat me to it! Better solution too 
wow, it works great!
Didn’t knew varags function unwarps dictionary and It can be used such way 
Thank you!
No, that’s not what’s going on; the varargs is just because the merge methods in Base also support merging multiple dictionaries at once, and in fact that’s the functionality you’re using by splatting the 5-element x vector. It may be more instructive to compare two-argument versions of recursive_merge and the merge(merge, x...) you already came up with:
recursive_merge(x1::AbstractDict, x2::AbstractDict) = merge(recursive_merge, x1, x2)
not_so_recursive_merge(x1::AbstractDict, x2::AbstractDict) = merge(merge, x1, x2)
I’ll let you think about the difference for a bit; as a hint, to untangle things and simplify the thought process it may be helpful to think of merge(x1, x2) and merge(combine, x1, x2) as a completely different functions (e.g., with the latter called merge_with_combine(combine, x1, x2).
1 Like
In case that there is duplicate key in one of the dicts, the above example of recursive_merge fails with
ERROR: MethodError: no method matching recursive_merge(::String, ::String)
If you add a second less specific method, you can even merge dictionaries with identical keys.
#recursively merge kw-dicts
recursive_merge(x::AbstractDict...) = merge(recursive_merge, x...)
# if values are not AbstractDicts, take the last definition (as does merge)
recursive_merge(x...) = x[end]
Here I chose to keep the last entry, because it follows the convention that has been chosen for merge.
3 Likes
For anyone who found this on Google while looking for a recursive merge of JSON-like data structures, here’s a third method which allows this to work with vectors (assume them to be unordered sets)
recursive_merge(x::AbstractDict...) = merge(recursive_merge, x...)
recursive_merge(x::AbstractVector...) = cat(x...; dims=1)
recursive_merge(x...) = x[end]
Example:
7 Likes
