# Weird behavior with "map" function
**URL:** https://discourse.julialang.org/t/weird-behavior-with-map-function/81816
**Category:** New to Julia
**Created:** [May 27, 2022, 8:39pm UTC](https://discourse.julialang.org/t/weird-behavior-with-map-function/81816 "2022-05-27T20:39:26Z")
**Posts on this page:** 6
**Page:** 1
### Author:  [@lancejnelson](https://discourse.julialang.org/u/lancejnelson)
#### Post date: [May 27, 2022, 8:39pm UTC](https://discourse.julialang.org/t/weird-behavior-with-map-function/81816/1 "2022-05-27T20:39:26Z")
Simple example:
```nohighlight
a = [5.4,2.7,8]
b = [5.3,2.1,"Jump"]
typeof(a) # Vector{Float64}
typeof(b) # Vector{Any}
```
just as expected. Now try using map function:
```nohighlight
map(typeof,[a,b])
```
produces this:
```nohighlight
2-element Vector{DataType}:
Vector{Any} (alias for Array{Any, 1})
Vector{Any} (alias for Array{Any, 1})
```
---
### Author:  [@Oscar\_Smith](https://discourse.julialang.org/u/Oscar_Smith)
#### Post date: [May 27, 2022, 8:43pm UTC](https://discourse.julialang.org/t/weird-behavior-with-map-function/81816/2 "2022-05-27T20:43:27Z")
What you’re missing is `[a,b]` promotes.
---
### Author:  [@lancejnelson](https://discourse.julialang.org/u/lancejnelson)
#### Post date: [May 27, 2022, 8:58pm UTC](https://discourse.julialang.org/t/weird-behavior-with-map-function/81816/3 "2022-05-27T20:58:21Z")
👍 👊 Thanks
---
### Author:  [@lancejnelson](https://discourse.julialang.org/u/lancejnelson)
#### Post date: [May 27, 2022, 9:01pm UTC](https://discourse.julialang.org/t/weird-behavior-with-map-function/81816/4 "2022-05-27T21:01:34Z")
Although this seemed to work as expected:
```nohighlight
a = 5.6 #Float
b = 1 #Integer
c = false # bool
d = "Jump" # string
e = 1//2 # Rational
[a,b,c,d,e] .|> typeof
```
I suppose there is no promotion rule for string and bool
---
### Author:  [@StefanKarpinski](https://discourse.julialang.org/u/StefanKarpinski)
#### Post date: [May 27, 2022, 9:30pm UTC](https://discourse.julialang.org/t/weird-behavior-with-map-function/81816/5 "2022-05-27T21:30:10Z")
What would the promotion of String and Bool be?
---
### Author:  [@Benny](https://discourse.julialang.org/u/Benny)
#### Post date: [May 28, 2022, 2:03am UTC](https://discourse.julialang.org/t/weird-behavior-with-map-function/81816/6 "2022-05-28T02:03:53Z")
It _is_ kind of weird to me that `Vector{Float64}` is promoted to `Vector{Any}`. It doesn’t seem like there’d be a performance benefit to allocating a new array with an abstract element type (of course, promotion is easy to get around: `Any[a, b]`). Besides, it doesn’t look like promoting parameters happen in general:
```julia
mutable struct X{T}
y::T
end
a = X(1.5)
b = X{Any}(1)
f = [a,b]
#=
2-element Vector{X}:
X{Float64}(1.5)
X{Any}(1)
=#
```