Simple type/array problem

New to Julia
1

d = [1.3, 2., 3., 4.3]
dd =[1., 3.]
dd[2] = sum(q[t,1:5], dims=1);

This gives the following errow:

MethodError: Cannot convert an object of type Vector{Float64} to an object of type Float64
Closest candidates are:

  • convert(::Type{T}, ::T) where T<:Number at /Applications/Julia-1.7.app/Contents/Resources/julia/share/julia/base/number.jl:6*
  • convert(::Type{T}, ::Number) where T<:Number at /Applications/Julia-1.7.app/Contents/Resources/julia/share/julia/base/number.jl:7*
  • convert(::Type{T}, ::Base.TwicePrecision) where T<:Number at /Applications/Julia-1.7.app/Contents/Resources/julia/share/julia/base/twiceprecision.jl:262*

If i siply put
dd[2] = 2;
it works!

Thank you for helping me to fix this!

2

Your MWE is not complete:

julia> d = [1.3, 2., 3., 4.3]
4-element Vector{Float64}:
 1.3
 2.0
 3.0
 4.3

julia> dd =[1., 3.]
2-element Vector{Float64}:
 1.0
 3.0

julia> dd[2] = sum(q[t,1:5], dims=1);
ERROR: UndefVarError: q not defined
Stacktrace:
 [1] top-level scope
   @ REPL[3]:1

Post a runnable MWE with triple back-ticks

```
like this
```

and we can help you answer your question.

1 Like
3

This is like trying to do the following:

julia> dd = [1.0, 3.0];

julia> dd[2] = [1, 2, 3, 4, 5]
ERROR: MethodError: Cannot `convert` an object of type Vector{Int64} to an object of type Float64
Closest candidates are:
  convert(::Type{T}, ::T) where T<:Number at ~/programs/julia/julia-1.7.0/share/julia/base/number.jl:6
  convert(::Type{T}, ::Number) where T<:Number at ~/programs/julia/julia-1.7.0/share/julia/base/number.jl:7
  convert(::Type{T}, ::Base.TwicePrecision) where T<:Number at ~/programs/julia/julia-1.7.0/share/julia/base/twiceprecision.jl:262
  ...
Stacktrace:
 [1] setindex!(A::Vector{Float64}, x::Vector{Int64}, i1::Int64)
   @ Base ./array.jl:903
 [2] top-level scope
   @ REPL[2]:1

I.e., sum(q[t,1:5], dims=1) results in an Array, not something that can be converted into a Float64.

EDIT: If t is a scalar, then q[t,1:5] is a Vector, in which case you can omit the dims keyword argument if you actually want the scalar output of the summation.

4

sorry I changed the example for the question. in the sum function q is supposed to be d.

5

…and what’s the t :wink: ?

If I remove the t I can do

d = [1.3, 2., 3., 4.3]
dd = [1., 3.]

but then

sum(d[1:4], dims=1)
1-element Vector{Float64}:
 10.6

since summing over dimensions “collapses” them to size 1, but does still keep the array structure (vector here)

For a vector you could

julia> sum(d)
10.6

to actually get a number. This can be put into dd[2] (where you just can “store” numbers but not vectors, since dd is a vector of numbers).

So one solution (depending on your larger setting) could be

dd[2] = sum(d)