Stream: helpdesk (published)

Topic: Add Values to Dict Arrays

brett knoss (May 30 2021 at 23:14):

Is there a way to add a value to every array in a Dictionary?

mbaz (May 31 2021 at 01:33):

julia> d = Dict(:a => 1, :b => [1 2 ; 3 4], :c => "x")
Dict{Symbol, Any} with 3 entries:
  :a => 1
  :b => [1 2; 3 4]
  :c => "x"

julia> for k in keys(d)
         if d[k] isa Array
             d[k] .+= 1
         end
       end

julia> d
Dict{Symbol, Any} with 3 entries:
  :a => 1
  :b => [2 3; 4 5]
  :c => "x"

julia>

brett knoss (May 31 2021 at 04:16):

No, I want to add a zero to every array in my dictionary, not add 1 to every value in my dictionary

brett knoss (May 31 2021 at 04:23):

 d = Dict(:a => 1, :b => [1 2 ; 3 4], :c => "x")
Dict{Symbol, Any} with 3 entries:
  :a => 1
  :b => [1 2; 3 4]
  :c => "x"

Dict{Symbol, Any} with 3 entries:
  :a => 1,0
  :b => [1 2; 3 4,0]
  :c => ["x",0]

Brenhin Keller (May 31 2021 at 04:37):

It's a pretty simple extrapolation from there

brett knoss (May 31 2021 at 17:25):

I'm not sure how you mean

Andrey Oskin (May 31 2021 at 17:35):

You can use any operation, with the same approach.

Nothing changes if you switch from adding 1 to appending a zero.

mbaz (May 31 2021 at 18:59):

@brett knoss It would help if you used the standard terminology: a dictionary is made up of keys and values. For example, in Dict("abc" => 42), "abc" is a key and 42 its corresponding value.

So, I assume you have a dictionary where all values are vectors, and you want to append a zero to each one. All you have to do is iterate over the values:

julia> d = Dict(:a => [], :b => [1, 2, 3])
Dict{Symbol, Vector{T} where T} with 2 entries:
  :a => Any[]
  :b => [1, 2, 3]

julia> for v in values(d)
            append!(v, 0)
          end

julia> d
Dict{Symbol, Vector{T} where T} with 2 entries:
  :a => Any[0]
  :b => [1, 2, 3, 0]

Unless you are sure that all values are vectors with elements that are either numerical or Any, you'll have to be careful with the types:

julia> append!(["a", "b", "c"], 0)
ERROR: MethodError: Cannot `convert` an object of type Int64 to an object of type String
...

julia> append!([1 2 ; 3 4], 0)
ERROR: MethodError: no method matching append!(::Matrix{Int64}, ::Int64)
...

Brenhin Keller (May 31 2021 at 23:51):

For learning how to generalize things like this there some pretty good introductory resources including books
https://benlauwens.github.io/ThinkJulia.jl/latest/book.html
https://leanpub.com/julia-for-beginners
as well as free classes and excersies
https://juliaacademy.com/courses
https://exercism.io/tracks/julia

For terminology issues like the difference between "add" and "append" this is actually quite consistent between different programming languages, so introductory resources for other languages could be helpful there too.

peter j. (Jun 03 2021 at 18:07):

I think Dictionaries.jl also has an interface that does this more efficiently, if that is needed.

Last updated: Oct 02 2023 at 04:34 UTC