Syntax#

This notebook briefly goes over basic syntax in Julia.

Differences from Python#

This page summarises the main differences between Julia and Python: https://docs.julialang.org/en/v1/manual/noteworthy-differences/#Noteworthy-differences-from-Python

Basic Types#

A = 3.14  # `Float64`

3.14

B = 10  # `Int64`

10

C = "hello"  # `String`

"hello"

'h'  # `Character`

'h': ASCII/Unicode U+0068 (category Ll: Letter, lowercase)

D = C[1]  # Strings are collections of `Character`s

'h': ASCII/Unicode U+0068 (category Ll: Letter, lowercase)

E = true  # `Boolean`

true

typeof(A)  # Find the type of a variable

Float64

supertype(Integer)  # Find supertypes

Real

subtypes(Integer)  # Find subtypes

3-element Vector{Any}:
 Bool
 Signed
 Unsigned

Integer <: Real  # Check if something is a “Subtype of”

true

:something  # Symbol for a name or label

:something

Arithmetic#

2 + 2 - 1 == 3

true

2^2 == 4

true

sqrt(9) == 3

true

10 / 2 == 5.0

true

exp(π * im) ≈ -1  # NB: this is `\approx` (≈) not equals

true

Containers#

Lists, arrays, dictionaries, tuples, etc…

t = (1, 2, 3)  # Tuple (immutable)

(1, 2, 3)

t = (a=2, b=1 + 2)  # Named tuple, access: t.a

(a = 2, b = 3)

d = Dict(:A => 1, :B => 2)  # Dictionary

Dict{Symbol, Int64} with 2 entries:
  :A => 1
  :B => 2

a = [1, 2, 3, 4]  # 4-element Vector{Int64}

4-element Vector{Int64}:
 1
 2
 3
 4

Vector{Int64}(undef, 10)  # undef 1-D array length n

10-element Vector{Int64}:
 140308137896976
 140308137897008
 140308137897040
 140308137897072
 140308137897104
 140308137897136
 140308137897168
 140308137897200
 140308137897232
 140308137897264

Float64[1, 2]  # 2-element Vector{Float64}

2-element Vector{Float64}:
 1.0
 2.0

Array(1:5)  # 5-element Array{Int64,1}

5-element Vector{Int64}:
 1
 2
 3
 4
 5

[1:5;]  # 5-element Array{Int64,1}

5-element Vector{Int64}:
 1
 2
 3
 4
 5

[1:5]  # 1-element vector with a range

1-element Vector{UnitRange{Int64}}:
 1:5

a = [i^3 for i in [1, 2, 3]]  # Array comprehension

3-element Vector{Int64}:
  1
  8
 27

[range(0, stop=2π, length=5);]  # 5-element Vector{Float64}

5-element Vector{Float64}:
 0.0
 1.5707963267948966
 3.141592653589793
 4.71238898038469
 6.283185307179586

rand(5)  # random 5-elem vector in [0,1)

5-element Vector{Float64}:
 0.5191453942059896
 0.1172917547222545
 0.400891263220127
 0.46935731766886424
 0.6427127357180475

rand(Int, 5)  # random vector with integers

5-element Vector{Int64}:
  9023148357981655655
 -9209514901102199357
 -4932026185504444220
  3427665566901318944
  6579442520360223700

ones(5)  # 5-elem vector with FP64 ones

5-element Vector{Float64}:
 1.0
 1.0
 1.0
 1.0
 1.0

zeros(5)  # 5-elem vector with FP64 zeros

5-element Vector{Float64}:
 0.0
 0.0
 0.0
 0.0
 0.0

[1, 2, 3] .^ 2  # Element-wise dot-operation

3-element Vector{Int64}:
 1
 4
 9

Array{Float16,2}(undef, 2, 3)  # New undef array type `T`, elements `dims`

2×3 Matrix{Float16}:
 -0.004456  NaN    1.13e-6
 -0.0637      0.0  0.0

mat = [1 2; 3 4]  # 2×2 Matrix{Int64}

2×2 Matrix{Int64}:
 1  2
 3  4

zeros(4, 4, 4, 4)  # Zero 4×4×4×4 Array{Float64,4}

4×4×4×4 Array{Float64, 4}:
[:, :, 1, 1] =
 0.0  0.0  0.0  0.0
 0.0  0.0  0.0  0.0
 0.0  0.0  0.0  0.0
 0.0  0.0  0.0  0.0

[:, :, 2, 1] =
 0.0  0.0  0.0  0.0
 0.0  0.0  0.0  0.0
 0.0  0.0  0.0  0.0
 0.0  0.0  0.0  0.0

[:, :, 3, 1] =
 0.0  0.0  0.0  0.0
 0.0  0.0  0.0  0.0
 0.0  0.0  0.0  0.0
 0.0  0.0  0.0  0.0

[:, :, 4, 1] =
 0.0  0.0  0.0  0.0
 0.0  0.0  0.0  0.0
 0.0  0.0  0.0  0.0
 0.0  0.0  0.0  0.0

[:, :, 1, 2] =
 0.0  0.0  0.0  0.0
 0.0  0.0  0.0  0.0
 0.0  0.0  0.0  0.0
 0.0  0.0  0.0  0.0

[:, :, 2, 2] =
 0.0  0.0  0.0  0.0
 0.0  0.0  0.0  0.0
 0.0  0.0  0.0  0.0
 0.0  0.0  0.0  0.0

[:, :, 3, 2] =
 0.0  0.0  0.0  0.0
 0.0  0.0  0.0  0.0
 0.0  0.0  0.0  0.0
 0.0  0.0  0.0  0.0

[:, :, 4, 2] =
 0.0  0.0  0.0  0.0
 0.0  0.0  0.0  0.0
 0.0  0.0  0.0  0.0
 0.0  0.0  0.0  0.0

[:, :, 1, 3] =
 0.0  0.0  0.0  0.0
 0.0  0.0  0.0  0.0
 0.0  0.0  0.0  0.0
 0.0  0.0  0.0  0.0

[:, :, 2, 3] =
 0.0  0.0  0.0  0.0
 0.0  0.0  0.0  0.0
 0.0  0.0  0.0  0.0
 0.0  0.0  0.0  0.0

[:, :, 3, 3] =
 0.0  0.0  0.0  0.0
 0.0  0.0  0.0  0.0
 0.0  0.0  0.0  0.0
 0.0  0.0  0.0  0.0

[:, :, 4, 3] =
 0.0  0.0  0.0  0.0
 0.0  0.0  0.0  0.0
 0.0  0.0  0.0  0.0
 0.0  0.0  0.0  0.0

[:, :, 1, 4] =
 0.0  0.0  0.0  0.0
 0.0  0.0  0.0  0.0
 0.0  0.0  0.0  0.0
 0.0  0.0  0.0  0.0

[:, :, 2, 4] =
 0.0  0.0  0.0  0.0
 0.0  0.0  0.0  0.0
 0.0  0.0  0.0  0.0
 0.0  0.0  0.0  0.0

[:, :, 3, 4] =
 0.0  0.0  0.0  0.0
 0.0  0.0  0.0  0.0
 0.0  0.0  0.0  0.0
 0.0  0.0  0.0  0.0

[:, :, 4, 4] =
 0.0  0.0  0.0  0.0
 0.0  0.0  0.0  0.0
 0.0  0.0  0.0  0.0
 0.0  0.0  0.0  0.0

rand(12, 4);  # Random 12×4 Matrix{Float64}

Indexing#

a[1]  # first element

1

a[1:3]  # 3-element vector

3-element Vector{Int64}:
  1
  8
 27

a[3:end]  # end is last element

1-element Vector{Int64}:
 27

a[1:2:end]  # step size of 2

2-element Vector{Int64}:
  1
 27

a[3:end]  # end is last element

1-element Vector{Int64}:
 27

Functions#

length(a)

3

first(a)

1

last(a)

27

minimum(a)

1

maximum(a)

27

argmin(a)

1

argmax(a)

3

size(a)

(3,)

push!(a, 10)  # Append in-place

4-element Vector{Int64}:
  1
  8
 27
 10

insert!(a, 1, 42)  # Insert in given position

5-element Vector{Int64}:
 42
  1
  8
 27
 10

append!(a, [3, 5, 7])  # Append another array

8-element Vector{Int64}:
 42
  1
  8
 27
 10
  3
  5
  7

splice!(a, 3, -1)  # Rm in given pos and replace

8

Loops and Conditionals#

# Basic looping over a list
for i in [1, 2, 3, 4, 5]
    println("i = $i")
end

i = 1
i = 2
i = 3
i = 4
i = 5

# Looping over a list, by index
A = [1 2; 3 4]
for i in eachindex(A)
    println("i = $i, A[i] = $(A[i])")
end

i = 1, A[i] = 1
i = 2, A[i] = 3
i = 3, A[i] = 2
i = 4, A[i] = 4

# Loop through key-value pairs in a dictionary
for (k, v) in Dict("A" => 1, "B" => 2, "C" => 3)
    println("$k is $v")
end

B is 2
A is 1
C is 3

if 1 == 10
    println("Something is wrong")
elseif 1 == 1
    println("Sounds right!")
end

Sounds right!

References#