# List comprehension Dictionary Julia

**URL:** <https://discourse.julialang.org/t/list-comprehension-dictionary-julia/11129>\
**Category:** General Usage\
**Created:** [May 24, 2018, 3:14pm UTC](https://discourse.julialang.org/t/list-comprehension-dictionary-julia/11129 "2018-05-24T15:14:41Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![jayce\_ram](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/jayce_ram/32/3977_2.png) [@jayce\_ram](https://discourse.julialang.org/u/jayce_ram)\
**Post date:** [May 24, 2018, 3:14pm UTC](https://discourse.julialang.org/t/list-comprehension-dictionary-julia/11129/1 "2018-05-24T15:14:41Z")

</div>

I have a set of years like that:

```julia
years = [2020,2021,2022]

```

and I also have a dictionary that links the sites available in each year(sit\_available\_year), that looks like following :

```julia
2020 -> ["site1","site2,"site3]
2021 -> ["site1","site3"]

```

I’d like to create a dictionary that seems like that:

```julia
myDict= Dict(((site,y)) => value1 for y in years, site in sit_available_year[y])

```

the keys of my dictionary it will be then:

```julia
["site1", 2020] => value1 
["site2", 2020] => value1 
["site1", 2021] => value1 

```

I have tried that syntax above but it doesn’t work. I got an error that says that y is not defined.  
Anyone has an idea what’s the right syntax to use? Thanks in advance.

---

<div class="post-metadata">

**Author:** ![mauro3](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/mauro3/32/292_2.png) [@mauro3](https://discourse.julialang.org/u/mauro3)\
**Post date:** [May 24, 2018, 3:35pm UTC](https://discourse.julialang.org/t/list-comprehension-dictionary-julia/11129/2 "2018-05-24T15:35:24Z")

</div>

I don’t think you can refer to the value of one of the iterators in the other. Just use a loop:

```julia
julia> a = []                                                                                                                                                            
0-element Array{Any,1}                                                                                                                                                   
                                                                                                                                                                         
julia> for y in 7:8, site in 1:y
       push!(a, (site,y) => 4)
       end                                                                                                                                                               
                                                                                                                                                                         
julia> Dict(a...)
Dict{Tuple{Int64,Int64},Int64} with 15 entries:
  (1, 7) => 4                                                                                                                                                            
  (4, 7) => 4                                                                                                                                                            
  (6, 8) => 4                                                                                                                                                            
  (8, 8) => 4                                                                                                                                                            
  (2, 8) => 4                                                                                                                                                            
  (5, 8) => 4                                                                                                                                                            
  (4, 8) => 4
  (7, 8) => 4                                                                                                                                                            
  (1, 8) => 4                                                                                                                                                            
  (6, 7) => 4
  (7, 7) => 4                                                                                                                                                            
  (3, 7) => 4                                                                                                                                                            
  (2, 7) => 4                                                                                                                                                            
  (3, 8) => 4
  (5, 7) => 4

```

(Next time, also make self-contained minimal working examples.)

---

<div class="post-metadata">

**Author:** ![korsbo](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/korsbo/32/15942_2.png) [@korsbo](https://discourse.julialang.org/u/korsbo)\
**Post date:** [May 24, 2018, 3:43pm UTC](https://discourse.julialang.org/t/list-comprehension-dictionary-julia/11129/3 "2018-05-24T15:43:44Z")

</div>

```julia
years = [2020,2021]
d = Dict(
    2020 => ["site1", "site2", "site3"],
    2021 => ["site1", "site3"],
)

Dict((s, y) => 1 for y in years for s in d[y] )

```

gives you:

```julia
Dict{Tuple{String,Int64},Int64} with 5 entries:
  ("site1", 2021) => 1
  ("site1", 2020) => 1
  ("site2", 2020) => 1
  ("site3", 2021) => 1
  ("site3", 2020) => 1

```