# How to recursively update the values of a nested dictionary?

**URL:** <https://discourse.julialang.org/t/how-to-recursively-update-the-values-of-a-nested-dictionary/114855>\
**Category:** General Usage\
**Created:** [May 28, 2024, 3:55pm UTC](https://discourse.julialang.org/t/how-to-recursively-update-the-values-of-a-nested-dictionary/114855 "2024-05-28T15:55:00Z")\
**Posts on this page:** 4\
**Page:** 1

<div class="post-metadata">

**Author:** ![sylvaticus](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/sylvaticus/32/203883_2.png) [@sylvaticus](https://discourse.julialang.org/u/sylvaticus)\
**Post date:** [May 28, 2024, 3:55pm UTC](https://discourse.julialang.org/t/how-to-recursively-update-the-values-of-a-nested-dictionary/114855/1 "2024-05-28T15:55:00Z")

</div>

Let’s say I have a nested dictionary like :

```julia
a_nested_dict = Dict("a"=>1,"b"=>Dict("c"=>2,"d"=>[Dict("e"=>2),Dict("f"=>3)]),"g"=>[1,"h"])

```

How do I override individual values, using a function like:

```julia
function override_nested_dict!(nested_dict,override_elements)
    for o_element in override_elements
        ....
    end
end

```

Such to produce :

```julia
a_nested_dict["a"] = 10
a_nested_dict["g"][2] = "l"
a_nested_dict["b"]["d"][2] = Dict("i"=>4) 

```

In particular I don’t know the data structure of override\_elements… vector of pairs of tuples as key and values?

---

<div class="post-metadata">

**Author:** ![sylvaticus](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/sylvaticus/32/203883_2.png) [@sylvaticus](https://discourse.julialang.org/u/sylvaticus)\
**Post date:** [May 28, 2024, 4:00pm UTC](https://discourse.julialang.org/t/how-to-recursively-update-the-values-of-a-nested-dictionary/114855/2 "2024-05-28T16:00:16Z")

</div>

This one for example doesn’t work:

```julia
a_nested_dict = Dict("a"=>1,"b"=>Dict("c"=>2,"d"=>[Dict("e"=>2),Dict("f"=>3)]),"g"=>[1,"h"])

function override_nested_dict!(nested_dict,override_elements)
    for o_element in override_elements
        nested_dict[o_element[1]...] = o_element[2]
    end
end

override_nested_dict!(a_nested_dict,["a"=>10,("g",2)=>"l",("b","d",2)=>Dict("i"=>4)])

```

---

<div class="post-metadata">

**Author:** ![Jeff\_Emanuel](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/jeff_emanuel/32/15440_2.png) [@Jeff\_Emanuel](https://discourse.julialang.org/u/Jeff_Emanuel)\
**Post date:** [May 28, 2024, 4:06pm UTC](https://discourse.julialang.org/t/how-to-recursively-update-the-values-of-a-nested-dictionary/114855/3 "2024-05-28T16:06:44Z")

</div>

Your override specifications are pairs of either a key and a value, or a Tuple of keys and a value. Your base case is when the `first` of the pair is not a tuple, set the key/value pair in the Dict. If the first is a tuple, then extract the first element from the tuple, use it to look up an inner Dict, then recursively do the same with the remaining elements of the Tuple and the inner Dict until you have a single element left in the Tuple. Then follow the base case.

---

<div class="post-metadata">

**Author:** ![sylvaticus](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/sylvaticus/32/203883_2.png) [@sylvaticus](https://discourse.julialang.org/u/sylvaticus)\
**Post date:** [May 29, 2024, 4:51am UTC](https://discourse.julialang.org/t/how-to-recursively-update-the-values-of-a-nested-dictionary/114855/4 "2024-05-29T04:51:10Z")

</div>

Thanks, this seems to work:

```julia
julia> function override_nested_dict!(nested_dict,override_elements)
           for o_element in override_elements
               td = nested_dict
               o_ks = o_element[1]; o_v = o_element[2];
               (typeof(o_ks) <: Tuple) || (o_ks = (o_ks,))
               for (ik,k) in enumerate(o_ks)
                   k in keys(td) || error("Override error: Key $k not found in container $td")
                   ik == length(o_ks) ? (td[k] = o_v) : (td = td[k]) 
               end
           end
       end
override_nested_dict! (generic function with 1 method)

julia> a_nested_dict = Dict("a"=>1,"b"=>Dict("c"=>2,"d"=>[Dict("e"=>2),Dict("f"=>3)]),"g"=>[1,"h"])
Dict{String, Any} with 3 entries:
  "g" => Any[1, "h"]
  "b" => Dict{String, Any}("c"=>2, "d"=>[Dict("e"=>2), Dict("f"=>3)])
  "a" => 1

julia> override_elements = ["a"=>10,("g",2)=>"l",("b","d",2)=>Dict("i"=>4)]
3-element Vector{Pair{Any, Any}}:
           "a" => 10
      ("g", 2) => "l"
 ("b", "d", 2) => Dict("i" => 4)

julia> override_nested_dict!(a_nested_dict,override_elements)

julia> a_nested_dict
Dict{String, Any} with 3 entries:
  "g" => Any[1, "l"]
  "b" => Dict

julia> override_elements2 = ["z"=>20]
1-element Vector{Pair{String, Int64}}:
 "z" => 20

julia> override_nested_dict!(a_nested_dict,override_elements2)
ERROR: Override error: Key z not found in container Dict{String, Any}("g" => Any[1, "l"], "b" => Dict{String, Any}("c" => 2, "d" => [Dict("e" => 2), Dict("i" => 4)]), "a" => 10)
Stacktrace:
 [1] error(s::String)
   @ Base ./error.jl:35
 [2] override_nested_dict!(nested_dict::Dict{String, Any}, override_elements::Vector{Pair{String, Int64}})
   @ Main ./REPL[19]:7
 [3] top-level scope
   @ REPL[25]:1

```