# How to best assign values to multiple locations in a Vector of Vectors?
**URL:** https://discourse.julialang.org/t/how-to-best-assign-values-to-multiple-locations-in-a-vector-of-vectors/118607
**Category:** New to Julia
**Tags:** arrays, vector-of-vectors
**Created:** [August 26, 2024, 3:27am UTC](https://discourse.julialang.org/t/how-to-best-assign-values-to-multiple-locations-in-a-vector-of-vectors/118607 "2024-08-26T03:27:20Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@oscarvdvelde](https://discourse.julialang.org/u/oscarvdvelde)
#### Post date: [August 26, 2024, 3:27am UTC](https://discourse.julialang.org/t/how-to-best-assign-values-to-multiple-locations-in-a-vector-of-vectors/118607/1 "2024-08-26T03:27:20Z")
I am looking for an equivalent to `myvector[locations] .= myvalue` for a vector of vectors. It seems that I can assign to one location at a time. Is there a way?
```julia
myvecvec = [Int64[] for i in 1:10]
myvecvec[2] = [1,2] # ok
locations = [3,5,6]
julia> myvecvec[locations] .= [7,8,9]
ERROR: MethodError: Cannot `convert` an object of type Int64 to an object of type Vector{Int64}
```
The error message seems wrong in that none of the lefthand or righthand side is an Int64?
Is this the preferred way?
```julia
[myvecvec[loc] = [7,8,9] for loc in locations]
```
and, subsequently, how can I make sure the `myvalue` which can be a single value or a vector, is made a vector (i.e. not `[myvalue]` as it errors when it already is a vector, and `collect(myvalue)` returns a zero-dimensional array for one value). Update: solved by this:
```julia
[length(myvalue)==1 ? myvecvec[loc] = [myvalue] : myvecvec[loc] = myvalue for loc in locations]
```
---
### Author:  [@abraemer](https://discourse.julialang.org/u/abraemer)
#### Post date: [August 26, 2024, 4:17am UTC](https://discourse.julialang.org/t/how-to-best-assign-values-to-multiple-locations-in-a-vector-of-vectors/118607/2 "2024-08-26T04:17:01Z")
> [@oscarvdvelde](#):
>
> The error message seems wrong in that none of the lefthand or righthand side is an Int64?
No the message is right. Julia tries to broadcast the elements of the vector on the right across the provided locations. This results in trying to slot `Int`s into the place of a `Vector{Int}` which causes the error. Note that this only happens because the Vector happens to be as long as the number of locations you provided. Try it with more or less locations to see what the error will say 🙂
> [@oscarvdvelde](#):
>
> Is this the preferred way?
>
> ```julia
> [myvecvec[loc] = [7,8,9] for loc in locations]
>
> ```
No definitively not. Side effects in array comprehensions is a very bad style imo. Additionally this allocates a new vector of vectors temporarily.
A simple way of achieving this multiple assignment is wrapping the right hand-side in `Ref`. This is the canonical way of telling that you don’t want to broadcast over the contents of something. So try:
```julia
myvecvec[locations] .= Ref([7,8,9])
```
Note that this really assigns them **same** vector to the slots in `myvecvec`. So if you mutate one of them all of them change:
```julia
myvecvec[locations[1]][2] = 1
myvecvec[locations[2]] # gives [7,1,9]
```
If you want separate copies, then I’d recommend just writing the for loop. Loops in Julia are fast. In fact broadcasting is implemented in Julia itself as a for loop.
> [@oscarvdvelde](#):
>
> Update: solved by this:
>
> ```julia
> [length(myvalue)==1 ? myvecvec[loc] = [myvalue] : myvecvec[loc] = myvalue for loc in locations]
>
> ```
This does not work for vectors of length 1. Just use `x isa Int` to check whether `x` is a `Int` or use the dispatch features of Julia.
---
### Author:  [@oscarvdvelde](https://discourse.julialang.org/u/oscarvdvelde)
#### Post date: [August 26, 2024, 4:23am UTC](https://discourse.julialang.org/t/how-to-best-assign-values-to-multiple-locations-in-a-vector-of-vectors/118607/3 "2024-08-26T04:23:34Z")
Thanks a lot for your answer!