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March 03, 2025 00:19
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Julia Cheatsheet

A comprehensive cheat sheet for the Julia programming language, covering syntax, data types, control flow, functions, and more. Designed for quick reference and efficient learning.

Basics and Syntax

Basic Syntax

Comments

# Single-line comment
#= … =# Multi-line comment

Variables

x = 10 Assignment
x Variable name (case-sensitive)

Operators

+, -, *, /, ^ Arithmetic operators
==, !=, <, >, <=, >= Comparison operators
&&, ||, ! Logical operators

Line Endings

Statements can be on the same line if separated by ;

String literals

"Hello, world!" String literals

String interpolation

"The value of x is $(x)"

Data Types

Numeric Types: Int64, Float64, ComplexF64, BigInt, BigFloat

Boolean: true, false

String: String

Character: Char

Arrays: Array{Type, N}

Tuples: Tuple{Type1, Type2, ...}

Dictionaries: Dict{KeyType, ValueType}

Symbols: :symbol

Control Flow

Conditional Statements 

if condition
  # code
elseif condition
  # code
else
  # code
end

condition ? value_if_true : value_if_false

Loops

For Loop

 
for i in 1:10
  println(i)
end

While Loop

 
i = 1
while i <= 10
  println(i)
  i += 1
end

Break/Continue

break - Exit the loop
continue - Skip to the next iteration

Exception Handling 

try
  # code that might throw an error
catch e
  # handle the error
finally
  # code that always runs
end

throw(ErrorException("message")) - Throw an exception

Functions

Function Definition 

function my_function(arg1, arg2)
  # function body
  return result
end

my_function(arg1, arg2) = arg1 + arg2  # Shorthand definition

Arguments

Positional Arguments

Arguments passed in the order they are defined.

Keyword Arguments

 
function my_function(; kwarg1=default_value, kwarg2)
  # function body
end

Default Argument Values

 
function my_function(arg1, arg2=default_value)
  # function body
end

Varargs

 
function my_function(args...)
  # function body
end

Return Values

return value - Explicitly return a value
If no return statement, the last evaluated expression is returned.

Multiple return values using tuples:

return (value1, value2)

Anonymous Functions 

x -> x^2  # Anonymous function that squares its argument

Arrays and Data Structures

Arrays

Creating Arrays

 
a = [1, 2, 3]        # 1D array
a = [1 2 3; 4 5 6]  # 2D array
a = Array{Float64}(undef, (3, 3)) # uninitialized 3x3 array

Indexing

Arrays are 1-indexed.
a[1] - First element
a[1:3] - Slice from 1 to 3
a[:, 1] - All rows, first column

Array Operations

+, -, *, / Element-wise operations
.*, ./, .^ Broadcasting operations
size(a) Dimensions of array a
length(a) Length of array a

Dictionaries

Creating Dictionaries

 
d = Dict("a" => 1, "b" => 2)

Accessing Values

d["a"] - Access value for key “a”

Adding/Updating Values

d["c"] = 3 - Add a new key-value pair
d["a"] = 4 - Update existing value

Checking for Key

haskey(d, "a") - Check if key “a” exists

Tuples 

t = (1, "hello", 3.14) # Creating a tuple

t[1] - Accessing tuple elements (1-indexed)

Tuples are immutable.