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vectorjulia
Anarcho-Chossid
Anarcho-Chossid

Reputation: 2330

Julia: append to an empty vector

I would like to create an empty vector and append to it an array in Julia. How do I do that?

x = Vector{Float64}
append!(x, rand(10))

results in

`append!` has no method matching append!(::Type{Array{Float64,1}}, ::Array{Float64,1})

Thanks.

Upvotes: 53

Views: 117444

Answers (5)

Friedrich -- Слава Україні
Friedrich -- Слава Україні

Reputation: 3734

A summary of various possibilities to create an empty float array and to "append":

x = Float64[] 
x = zeros()
x = zeros(0)
x = ones()
x = ones(0)
x = [0.][1:0]

a = [0., 10.]

append!(x, a)
push!(x, a...)
x = [x..., a...]
x = vcat(x, a)

Upvotes: 0

japamat
japamat

Reputation: 720

I am somewhat new to Julia and came across this question after getting a similar error. To answer the original question for Julia version 1.2.0, all that is missing are ():

x = Vector{Float64}()
append!(x, rand(10))

This solution (unlike x=zeros(0)) works for other data types, too. For example, to create an empty vector to store dictionaries use:

d = Vector{Dict}()
push!(d, Dict("a"=>1, "b"=>2))

A note regarding use of push! and append!:

According to the Julia help, push! is used to add individual items to a collection, while append! adds an collection of items to a collection. So, the following pieces of code create the same array:

Push individual items:

a = Vector{Float64}()
push!(a, 1.0)
push!(a, 2.0)

Append items contained in an array:

a = Vector{Float64}()
append!(a, [1.0, 2.0])

Upvotes: 50

chasmani
chasmani

Reputation: 2510

New answer, for Julia 1. append! is deprecated, you now need to use push!(array, element) to add elements to an array

my_stuff = zeros()
push!(my_stuff, "new element")

Upvotes: 8

Daniel Høegh
Daniel Høegh

Reputation: 716

You can initialize an empty Vector of any type by typing the type in front of []. Like:

Float64[] # Returns what you want
Array{Float64, 2}[] # Vector of Array{Float64,2}
Any[] # Can contain anything

Upvotes: 15

Vincent Zoonekynd
Vincent Zoonekynd

Reputation: 32351

Your variable x does not contain an array but a type.

x = Vector{Float64}
typeof(x)  # DataType

You can create an array as Array(Float64, n) (but beware, it is uninitialized: it contains arbitrary values) or zeros(Float64, n), where n is the desired size.

Since Float64 is the default, we can leave it out. Your example becomes:

x = zeros(0)
append!( x, rand(10) )

Upvotes: 58

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