How do you generate a regular non-integer sequence in julia? - julia

Question

How are regular, non-integer sequences generated in julia?
I'm trying to get 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
In MATLAB, I would use
0.1:0.1:1
And in R
seq(0.1, 1, by = 0.1)
But I can't find anything except integer sequences in julia (e.g., 1:10). Searching for "sequence" in the docs only gives me information about how strings are sequences.

Answer 1

Similarly to Matlab, but with the difference that 0.1:0.1:1 defines a Range:
julia> typeof(0.1:0.1:1)
Range{Float64} (constructor with 3 methods)
and thus if an Array is needed:
julia> [0.1:0.1:1]
10-element Array{Float64,1}:
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
Unfortunately, this use of Range is only briefly mentioned at this point of the documentation.
Edit: As mentioned in the comments by #ivarne it is possible to achieve a similar result using linspace:
julia> linspace(.1,1,10)
10-element Array{Float64,1}:
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
but note that the results are not exactly the same due to rounding differences:
julia> linspace(.1,1,10)==[0.1:0.1:1]
false

Answer 2

The original answer is now deprecated. You should use collect() to generate a sequence.
## In Julia
> collect(0:.1:1)
10-element Array{Float64,1}:
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
## In R
> seq(0, 1, .1)
[1] 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

Answer 3

They are generated the same way as in Matlab
julia> sequence = 0:.1:1
0.0:0.1:1.0
Alternatively, you can use the range() function, which allows you to specify the length, step size, or both
julia> range(0, 1, length = 5)
0.0:0.25:1.0
julia> range(0, 1, step = .01)
0.0:0.01:1.0
julia> range(0, step = .01, length = 5)
0.0:0.01:0.04
You can still do all of the thinks you would normally do with a vector, eg indexing
julia> sequence[4]
0.3
math and stats...
julia> sum(sequence)
5.5
julia> using Statistics
julia> mean(sequence)
0.5
This will (in most cases) work the same way as a vector, but nothing is actually allocated. It can be comfortable to make the vector, but in most cases you shouldn't (it's less performant). This works because
julia> sequence isa AbstractArray
true
If you truly need the vector, you can collect(), splat (...) or use a comprehension:
julia> v = collect(sequence)
11-element Array{Float64,1}:
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
julia> v == [sequence...] == [x for x in sequence]
true