Julia equivalent to python list multiplication

Question

In python I can quickly concatenate and create lists with repeated elements using the + and * operators. For example:

my_list = [1] * 3 + ['a'] * 4  # == [1, 1, 1, 'a', 'a', 'a', 'a']

Similarly in Julia, I can quickly concatenate and create strings with repeated elements using the * and ^ operators. For example:

my_string = "1"^3 * "a"^4  # == "111aaaa"

My question is whether or not there is a convenient equivalent for lists (arrays) in Julia. If not, then what is the simplest way to define arrays with repeated elements and concatenation?

check out fill()

JonSG
– JonSG

2022-03-14 19:39:38 +00:00
Commented Mar 14, 2022 at 19:39 — JonSG
– JonSG, Commented Mar 14, 2022 at 19:39

Przemyslaw Szufel · Accepted Answer · 2022-03-14 20:45:38Z

4

For the above scenario, a shorter form is fill:

[fill(1,3); fill('a', 4)]

You could also define a Python style operator if you like:

⊕(a::AbstractVector{T}, n::Integer) where T = repeat(a, n)
⊕(a::T, n::Integer) where T = fill(a, n)

The symbol ⊕ can be entered in Julia by typing \oplus and pressing Tab.

Now you can do just as in Python:

julia> [1,2] ⊕ 2
4-element Vector{Int64}:
 1
 2
 1
 2

julia> 3 ⊕ 2
2-element Vector{Int64}:
 3
 3

answered Mar 14, 2022 at 20:45

Przemyslaw Szufel

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SGJ · Accepted Answer · 2022-03-14 20:14:00Z

3

You can use repeat, e.g.

[repeat([1], 3); repeat(['a'],4)]

produces Any[1, 1, 1, 'a', 'a', 'a', 'a'].

answered Mar 14, 2022 at 20:14

SGJ

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