# Allocations in the loop
**URL:** https://discourse.julialang.org/t/allocations-in-the-loop/75310
**Category:** New to Julia
**Created:** [January 27, 2022, 5:30pm UTC](https://discourse.julialang.org/t/allocations-in-the-loop/75310 "2022-01-27T17:30:44Z")
**Posts on this page:** 5
**Page:** 1
### Author:  [@rukh79](https://discourse.julialang.org/u/rukh79)
#### Post date: [January 27, 2022, 5:30pm UTC](https://discourse.julialang.org/t/allocations-in-the-loop/75310/1 "2022-01-27T17:30:44Z")
Hello,
I am starting to learn Julia, and am puzzled by the allocations inside the loop. It seems that I only access values inside the loop and didn’t allocate anything. However, test1 allocated 1M and test2 allocated 22G.
Could anyone kindly help explain to me why?
Thank you!
```julia
function make_dictionary!(dict, vec)
for i in 0:9
dict[i] = Vector{Int}()
end
for m in eachindex(vec)
push!(dict[m % 10], m)
end
end
function test1(n)
vec = Vector(1:n)
dict = Dict()
make_dictionary!(dict, vec)
r = 0.0
end
function test2(n)
vec = Vector(1:n)
dict = Dict()
make_dictionary!(dict, vec)
r = 0.0
for r1 = 0:9
for r2 = 0:9
for m1 in dict[r1]
for m2 in dict[r2]
r += 1
end
end
end
end
r
end
@time test1(20000)
@time test2(20000)
```
---
### Author:  [@cstjean](https://discourse.julialang.org/u/cstjean)
#### Post date: [January 27, 2022, 5:43pm UTC](https://discourse.julialang.org/t/allocations-in-the-loop/75310/2 "2022-01-27T17:43:53Z")
`dict = Dict{Int, Vector{Int}}()` ? Because a `Dict()` can contain anything whatsoever, the `==` test it has to perform when using it is type-unstable (the compiler doesn’t know which method to call, so has to introduce a dynamic call), and that involves allocations.
---
### Author:  [@rukh79](https://discourse.julialang.org/u/rukh79)
#### Post date: [January 27, 2022, 6:44pm UTC](https://discourse.julialang.org/t/allocations-in-the-loop/75310/3 "2022-01-27T18:44:12Z")
Thank you for your reply! Would you please expand it a little more where “==” test was done?
Also why test3 (single loop other than double loop) has no such problems.
test1: 1M; test2: 22G; test3: 2M
```julia
function test3(n)
vec = Vector(1:n)
dict = Dict()
make_dictionary!(dict, vec)
r = 0.0
for r1 = 0:9
for m1 in dict[r1]
r += 1
end
end
r
end
```
---
### Author:  [@cstjean](https://discourse.julialang.org/u/cstjean)
#### Post date: [January 27, 2022, 6:54pm UTC](https://discourse.julialang.org/t/allocations-in-the-loop/75310/4 "2022-01-27T18:54:11Z")
> [@rukh79](#):
>
> Thank you for your reply! Would you please expand it a little more where “==” test was done?
A `Dict` is a hash table. To find the key, it first hashes the value you input, `r1`, which it knowns to be an Int. So far so good. It then looks up in that hash value’s bucket and finds a single key, of unknown type at compile-time (because your dict is a `Dict{Any, Any}`). To know that this key is indeed `r1`, it calls `==(r1::Int, that_key::Any)`. That’s a dynamic call. At runtime, it’ll figure out that `that_key` is also an `Int`, and call `==(::Int,::Int)`.
Your `test3` also allocates in the loop AFAICT. It’s just that because the loop isn’t nested, it doesn’t allocate as much.
---
### Author:  [@rukh79](https://discourse.julialang.org/u/rukh79)
#### Post date: [January 27, 2022, 7:01pm UTC](https://discourse.julialang.org/t/allocations-in-the-loop/75310/5 "2022-01-27T19:01:03Z")
Thank you!