Julia cheatsheet

Docs: https://docs.julialang.org/en/v1/

Data types

Data structure reference: https://juliacollections.github.io/DataStructures.jl/stable/

Array

create new array

a = Int64[]

or initialize directly

a = [] >> create new empty arraya = [1,2,3] >> create array of integers

create an array from 1 to 10

a = collect(1:10)print(a) >> [1,2,3,4,5,6,7,8,9,10]

create array of arrays (Vector)

vector = (Array{Int64, 1})[]

add to array

a = [1,2,3]push!(a, 5) >> [1,2,3,5]

add to Vector

vector = (Array{Int64, 1})[]push!(vector, [1,2,3], [25,26,27) >> [[1,2,3], [25,26,27]]

Dictionary

d = Dict(1=>"one", 2=>"two")

create with explicity type

d = Dict{Int64, String}()
d[0] = "joe"
d[1] = "mary"

check if dict has key

print(haskey(d, 1)) >> true

print dict values

print(values(d)) >> ["joe", "mary"]

loop thru Dict

for k in sort(collect(keys(d))) print(k, ": ", d[k])end

Structs

mutable struct Person name::String male::Bool age::Int children::Intendp = Person("Julia", false, 23, 3)people = Person[]push!(people, Person("Joe", true, 30, 2))push!(people, Person("Mary", false, 18, 0))

Utilities

get type of variable

typeof(myvar)

Map

get square root of each number

a = map((x) -> x^2, [1,2,3,4,5])print(a) >> [1,4,9,16,25]

Strings

mystring = "some text"

print a string

print(mystring)print("this is a variable here, ", mystring, " within a string")

upper case / lower case

print(uppercase(mystring))
print(lowercase(mystring))

get substring of string based on letter position

print(show(mystring[4])) >> "e"print(show(mystring[3:8])) >> "me tex"

string interpolation (include variable inside string)

a = "welcome"b = "julia"print("$a to $b, everybody") >> "welcome to julia, everybody"

run operation inside string

print("1+2 = $(1+2)") >> 1+2=3

concat string

s = string("to", "infinity", "and", "beyond")
print(s) >> "to infinity and beyond"

replace string

s = "the big black bear"print(replace(s, "black" => "polar")) >> "the big polar bear"

replace string with regex

print(replace(s, r"b[\w]*k" => "red")) >> "the big red bear"

split string into array

print(split(s)) >> ["the", "big", "black", "bear"]

split by delimeter

s = "blue, red, green"print(split(s, ",")) >> ["blue", "red", "green"]

combine an array into a String

r = join(collect(1:10), ", ") >> "1,2,3,4..10"

Conditional Statements

if / then

if var > 5 var = 0else print("continue")end

for loops

names = ["joe", "bob", "frank"]for name in names print(name)end

loop thru a range

x = 0

for k in 1:100

x = x + (1/k)^2

end

nested loop

for i in 1:3, j in 1:3

print("i = ", i, "j=", j, "\n")
end

break out of loop

for i in 1:100

if (i == 5) break end

end

continue next iteration

for i in [1,2,3]

if (i == 5) continue end

i = i + 2

end

Packages

install a new package into ~/.julia

import Pkg

Pkg.add("LinearAlgebra")

to use a pkg

using LinearAlgebra

install from REPL (cmd line)

julia

enter "]" key to get into pkg console

pkg> add <Package name>
pkg> rm <Package name>
pkg> update <pkg name> # or just "update" to update all pkgs

create a virtual env

julia # enter ] to enter pkg mode

pkg> generate <project name>

or 1 liner

julia -e 'using Pkg; Pkg.generate("my project name")'

activate virtualenv

cd to project root and
julia --project=.

now install packages within virtual env

julia, ]
pkg>add <pkg name>

force project to use pinned version of dependency

julia> Pkg.add("Pipe", preserve=PRESERVE_DIRECT)

or create a packages.jl file and execute to install

using Pkg

dependencies = ["IJulia", "Genie"]

Pkg.add(dependencies)

Logging

levels: warn, info, error, debug

@warn "test warning"

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