# Preallocate an array of tuples
**URL:** https://discourse.julialang.org/t/preallocate-an-array-of-tuples/54699
**Category:** General Usage
**Tags:** question
**Created:** [February 5, 2021, 5:34pm UTC](https://discourse.julialang.org/t/preallocate-an-array-of-tuples/54699 "2021-02-05T17:34:44Z")
**Posts on this page:** 8
**Page:** 1
### Author:  [@nelsonah](https://discourse.julialang.org/u/nelsonah)
#### Post date: [February 5, 2021, 5:34pm UTC](https://discourse.julialang.org/t/preallocate-an-array-of-tuples/54699/1 "2021-02-05T17:34:44Z")
This should be trivial but I’m stumped. Simple code snippet:
# points = Array{(UInt8, UInt8, UInt8)}(undef, x\_size, y\_size)
points = Array{undef,(6, 4)} # compiles, but not valid
val = (100, 225, 255)
points[2][3] = val # Fails on this line
Thanks
---
### Author:  [@jling](https://discourse.julialang.org/u/jling)
#### Post date: [February 5, 2021, 5:36pm UTC](https://discourse.julialang.org/t/preallocate-an-array-of-tuples/54699/2 "2021-02-05T17:36:49Z")
```julia
julia> val = (100, 225, 255)
(100, 225, 255)
julia> T = typeof(val) #use this info to determine type of array element
Tuple{Int64, Int64, Int64}
julia> points = Array{T, 2}(undef, 3,3)
3×3 Matrix{Tuple{Int64, Int64, Int64}}:
(0, 0, 0) (0, 0, 0) (0, 0, 0)
(0, 0, 0) (0, 0, 0) (0, 0, 0)
(0, 0, 0) (0, 0, 0) (0, 0, 0)
julia> points[2,3] = val
(100, 225, 255)
julia> points
3×3 Matrix{Tuple{Int64, Int64, Int64}}:
(0, 0, 0) (0, 0, 0) (0, 0, 0)
(0, 0, 0) (0, 0, 0) (100, 225, 255)
(0, 0, 0) (0, 0, 0) (0, 0, 0)
```
---
### Author:  [@DNF](https://discourse.julialang.org/u/DNF)
#### Post date: [February 5, 2021, 5:48pm UTC](https://discourse.julialang.org/t/preallocate-an-array-of-tuples/54699/3 "2021-02-05T17:48:13Z")
```julia
Matrix{NTuple{3, UInt8}}(undef, xsize, ysize)
```
`(UInt8, UInt8, UInt8)` isn’t a tuple type, but a tuple of types.
---
### Author:  [@stevengj](https://discourse.julialang.org/u/stevengj)
#### Post date: [February 5, 2021, 6:15pm UTC](https://discourse.julialang.org/t/preallocate-an-array-of-tuples/54699/4 "2021-02-05T18:15:53Z")
Alternatively,
```julia
Array{Tuple{UInt8, UInt8, UInt8}}(undef, x_size, y_size)
```
---
### Author:  [@nelsonah](https://discourse.julialang.org/u/nelsonah)
#### Post date: [February 5, 2021, 8:10pm UTC](https://discourse.julialang.org/t/preallocate-an-array-of-tuples/54699/5 "2021-02-05T20:10:18Z")
All 3 suggestions worked like a charm and were great.
I did have to change the points[2][3] = val % hangover from Python
to points[2, 3] = val
Many thanks. Harvey
---
### Author:  [@rdeits](https://discourse.julialang.org/u/rdeits)
#### Post date: [February 5, 2021, 8:25pm UTC](https://discourse.julialang.org/t/preallocate-an-array-of-tuples/54699/6 "2021-02-05T20:25:53Z")
> [@nelsonah](#):
>
> I did have to change the points[2][3] = val % hangover from Python
Yeah, `numpy` lets you treat a matrix as if it were also a list of lists, but in Julia those are separate concepts and therefore separate types. It does take a bit of getting used to, but I think it’s worth it.
---
### Author:  [@nelsonah](https://discourse.julialang.org/u/nelsonah)
#### Post date: [February 5, 2021, 8:30pm UTC](https://discourse.julialang.org/t/preallocate-an-array-of-tuples/54699/7 "2021-02-05T20:30:40Z")
I forgot to mention, Jliing hit a key issue. The elements of val were of type Int64, not UInt8.
Again, many thanks.
---
### Author:  [@DNF](https://discourse.julialang.org/u/DNF)
#### Post date: [February 5, 2021, 8:38pm UTC](https://discourse.julialang.org/t/preallocate-an-array-of-tuples/54699/8 "2021-02-05T20:38:14Z")
> [@nelsonah](#):
>
> I did have to change the points[2][3] = val % hangover from Python
You can do this in Python, but I think that `points[2, 3]` is the most idiomatic numpy.