# How to initialize and manipulate Dicts of Dicts?

**URL:** <https://discourse.julialang.org/t/how-to-initialize-and-manipulate-dicts-of-dicts/102788>\
**Category:** General Usage\
**Tags:** question\
**Created:** [August 14, 2023, 11:49am UTC](https://discourse.julialang.org/t/how-to-initialize-and-manipulate-dicts-of-dicts/102788 "2023-08-14T11:49:21Z")\
**Posts on this page:** 7\
**Page:** 1

<div class="post-metadata">

**Author:** ![trg818](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/trg818/32/219149_2.png) [@trg818](https://discourse.julialang.org/u/trg818)\
**Post date:** [August 14, 2023, 11:49am UTC](https://discourse.julialang.org/t/how-to-initialize-and-manipulate-dicts-of-dicts/102788/1 "2023-08-14T11:49:21Z")

</div>

I am trying to initialize and manipulate Dicts of Dicts, starting with this one:

```julia
using Dates
clcdates=Date(2022,7):Month(1):Date(2023,12)
dacc=Dict("MatA"=>Dict(Date(2022,7)=>751.19,Date(2023,1)=>7.98),
            "MatB"=>Dict(Date(2022,10)=>94.25));

```

So far, so good. Now I want to initialize another Dict of the same type and with the same keys, called `acc` that is supposed to record the temporal evolution of MatA and MatB in the timespan given by `clcdates`. Obviously, `acc` is much more densely populated than `dacc`, which holds only the changes that occur at irregular dates. I tried:

```julia
acc=begin
    for dak in keys(dacc)
        Dict(dak=>Dict(clcdates[1]=>0))
        for m in clcdates[2:end]
            Dict(dak=>Dict(clcdates[1]=>NaN))
        end
    end
end => Dict{String,Dict{Date,Float64}}()
mo=clcdates[1]
for (im,m) in enumerate(clcdates)
    for dak in keys(dacc)
        if haskey(dacc[dak],m)
            acc[dak][m]=acc[dak][mo]+dacc[dak][m] #
        elseif im > 1
            if acc[dak][mo] == 0
                acc[dak][m]=0
                acc[dak][mo]=NaN
            else
                acc[dak][m]=acc[dak][mo]
            end
        end
    end
    mo=m
end

```

This doesn’t work. `@show` tells me that after the `begin...end` block, I have `acc = nothing => Dict{String, Dict{Date, Float64}}()`, and then the first pass of the loop fails with:

```julia
MethodError: no method matching getindex(::Pair{Nothing, Dict{String, Dict{Date, Float64}}}, ::String)

Closest candidates are:
  getindex(::Pair, ::Int64)
   @ Base pair.jl:51
  getindex(::Pair, ::Real)
   @ Base pair.jl:52

Stacktrace:
 [1] top-level scope
   @ ./In[34]:18

```

Line 18 is the line I have marked with `#` at the end. What’s wrong here? Why is `acc` `nothing`, and what does the error message mean? Is the entire approach misguided?

---

<div class="post-metadata">

**Author:** ![oheil](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/oheil/32/220745_2.png) [@oheil](https://discourse.julialang.org/u/oheil)\
**Post date:** [August 14, 2023, 12:11pm UTC](https://discourse.julialang.org/t/how-to-initialize-and-manipulate-dicts-of-dicts/102788/2 "2023-08-14T12:11:08Z")

</div>

> [@trg818](#):
>
> ```julia-auto
> acc=begin
> for dak in keys(dacc)
> Dict(dak=>Dict(clcdates[1]=>0))
> for m in clcdates[2:end]
> Dict(dak=>Dict(clcdates[1]=>NaN))
> end
> end
> end => Dict{String,Dict{Date,Float64}}()
> 
> ```

It’s only a bit clear what you want to try here. But doing it just with a loop looks like:

```julia-auto
acc=Dict{String,Dict{Date,Float64}}()
for dak in keys(dacc)
   acc[dak]=Dict{Date,Float64}()
   for m in clcdates[1:end]
       acc[dak][m]=NaN
   end
end

```

Is this what you want to be `acc` in your first step? (I didn’t look into the next loop for now…)

---

<div class="post-metadata">

**Author:** ![trg818](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/trg818/32/219149_2.png) [@trg818](https://discourse.julialang.org/u/trg818)\
**Post date:** [August 14, 2023, 12:34pm UTC](https://discourse.julialang.org/t/how-to-initialize-and-manipulate-dicts-of-dicts/102788/3 "2023-08-14T12:34:27Z")

</div>

Not quite - I do indeed want the entries for the first date to be 0, not NaN (for reasons relating to the next loop). I had already tried something like that but was told that the key of the Dict (“MatB” in this case) was not found. I don’t understand that, because the initialization should have generated it, I think.

---

<div class="post-metadata">

**Author:** ![oheil](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/oheil/32/220745_2.png) [@oheil](https://discourse.julialang.org/u/oheil)\
**Post date:** [August 14, 2023, 1:45pm UTC](https://discourse.julialang.org/t/how-to-initialize-and-manipulate-dicts-of-dicts/102788/4 "2023-08-14T13:45:56Z")

</div>

> [@trg818](#):
>
> I do indeed want the entries for the first date to be 0, not NaN

Ok, this is just a special case. Just implement it in my proposal as you wish. But beware: 0 is an Int not a Float64.

---

<div class="post-metadata">

**Author:** ![trg818](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/trg818/32/219149_2.png) [@trg818](https://discourse.julialang.org/u/trg818)\
**Post date:** [August 14, 2023, 1:56pm UTC](https://discourse.julialang.org/t/how-to-initialize-and-manipulate-dicts-of-dicts/102788/5 "2023-08-14T13:56:07Z")

</div>

Well, as I said: I did, but the error I get is that the key is not known.

---

<div class="post-metadata">

**Author:** ![rocco\_sprmnt21](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/rocco_sprmnt21/32/20127_2.png) [@rocco\_sprmnt21](https://discourse.julialang.org/u/rocco_sprmnt21)\
**Post date:** [August 14, 2023, 3:11pm UTC](https://discourse.julialang.org/t/how-to-initialize-and-manipulate-dicts-of-dicts/102788/6 "2023-08-14T15:11:33Z")

</div>

```julia
acc=Dict{String,Dict{Date,Float64}}()
for dak in keys(dacc)
   acc[dak]=Dict{Date,Float64}()
   acc[dak][clcdates[1]]=0
   for m in clcdates[2:end]
       acc[dak][m]=NaN
   end
end

mo=clcdates[1]
for (im,m) in enumerate(clcdates)
    for dak in keys(dacc)
        if haskey(dacc[dak],m)
            acc[dak][m]=acc[dak][mo]+dacc[dak][m] #
        elseif im > 1
            if acc[dak][mo] == 0
                acc[dak][m]=0
                acc[dak][mo]=NaN
            else
                acc[dak][m]=acc[dak][mo]
            end
        end
    end
    mo=m
end

```

Using the code proposed by Oheil and the one written by you, this comes out.  
Is that what you wanted?

```julia
julia> acc["MatB"]
Dict{Date, Float64} with 18 entries:
  Date("2023-10-01") => 94.25
  Date("2022-10-01") => 94.25
  Date("2023-07-01") => 94.25
  Date("2022-11-01") => 94.25
  Date("2023-12-01") => 94.25
  Date("2023-02-01") => 94.25
  Date("2022-07-01") => NaN
  Date("2023-04-01") => 94.25
  Date("2023-11-01") => 94.25
  Date("2023-05-01") => 94.25
  Date("2023-01-01") => 94.25
  Date("2023-03-01") => 94.25
  Date("2023-08-01") => 94.25
  Date("2023-09-01") => 94.25
  Date("2022-08-01") => NaN
  Date("2022-12-01") => 94.25
  Date("2022-09-01") => 0.0
  Date("2023-06-01") => 94.25

julia> acc["MatA"]
Dict{Date, Float64} with 18 entries:
  Date("2023-10-01") => 759.17
  Date("2022-10-01") => 751.19
  Date("2023-07-01") => 759.17
  Date("2022-11-01") => 751.19
  Date("2023-12-01") => 759.17
  Date("2023-02-01") => 759.17
  Date("2022-07-01") => 751.19
  Date("2023-04-01") => 759.17
  Date("2023-11-01") => 759.17
  Date("2023-05-01") => 759.17
  Date("2023-01-01") => 759.17
  Date("2023-03-01") => 759.17
  Date("2023-08-01") => 759.17
  Date("2023-09-01") => 759.17
  Date("2022-08-01") => 751.19
  Date("2022-12-01") => 751.19
  Date("2022-09-01") => 751.19
  Date("2023-06-01") => 759.17

```

---

<div class="post-metadata">

**Author:** ![trg818](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/trg818/32/219149_2.png) [@trg818](https://discourse.julialang.org/u/trg818)\
**Post date:** [August 14, 2023, 3:47pm UTC](https://discourse.julialang.org/t/how-to-initialize-and-manipulate-dicts-of-dicts/102788/7 "2023-08-14T15:47:30Z")

</div>

Yes, that’s it more or less! Now I see that I stupidly missed an assignment to `acc` in the first loop and overwrote another one several times in that earlier attempt I didn’t show.  
Thank you very much!