Introduction to arrays

Introduction to Julia

James Fulton

Climate informatics researcher

What is an array?

# Store run times with many variables
runtime1 = 33.1
runtime2 = 32.7
runtime3 = 34.2
runtime4 = 31.9

# Store runtimes in array
runtimes = [33.1, 32.7, 34.2, 31.9]

List of values
Surrounded by [ ]
With , in beween values

Arrays vs. vectors vs. matrices

# Store runtimes in array
runtimes = [33.1, 32.7, 34.2, 31.9]

println(typeof(runtimes))

Vector{Float64}

Arrays vs. vectors vs. matrices

The image shows a vector as a one-dimensional line of values.

Arrays vs. vectors vs. matrices

The image shows a matrix as a two-dimensional grid of values.

Arrays vs. vectors vs. matrices

The image shows an array as a many-dimensional grid of values.

Array data types

# Store runtimes in array
runtimes = [33.1, 32.7, 34.2, 31.9]

println(typeof(runtimes))

Vector{Float64}

Array data types

# Store runtimes in array
runtimes = [33.1, 32.7, 34.2, 31.9]

println(eltype(runtimes))

Float64

Array data types

# Store integers in array
number_of_customers = [11, 19, 31, 27]

println(typeof(number_of_customers))

Vector{Int64}

# Store strings in array
names = ["Amit", "Barbara", "Carlos"]

println(typeof(names))

Vector{String}

# Store characters in array
grades = ['A', 'B', 'B', 'A']

println(typeof(grades))

Vector{Char}

# Store booleans in array
correct_answers = [true, false, true]

println(typeof(correct_answers))

Vector{Bool}

Mixed data types

# Store multiple types in array
#        string   bool  int char float
items = ["James", true, 10, 'B', -20.3]

println(typeof(items))

Vector{Any}

Mixed data types

# Store array of item names
item_names = ["chalk", "cheese", "eggs", "ham"]

# Store array of item prices
item_prices = [2.30, 3.50, 4.25, 2.00]

println(typeof(item_names))
println(typeof(item_prices))

Vector{String}
Vector{Float64}

Indexing arrays

# Index:         1        2        3       4
item_names = ["chalk", "cheese", "eggs", "ham"]

# Index:         1     2     3     4
item_prices = [2.30, 3.50, 4.25, 2.00]

println(item_names[1])
println(item_prices[1])

chalk
2.30

Indexing arrays

# Index:         1        2        3       4
item_names = ["chalk", "cheese", "eggs", "ham"]

# Index:         1     2     3     4
item_prices = [2.30, 3.50, 4.25, 2.00]

println(item_names[end])
println(item_prices[end])

ham
2.00

Indexing arrays

# Index:         1        2        3       4
item_names = ["chalk", "cheese", "eggs", "ham"]

# Index:         1     2     3     4
item_prices = [2.30, 3.50, 4.25, 2.00]

println(item_names[end-1])
println(item_prices[end-1])

eggs
4.25

Slicing arrays

# Index:         1        2        3       4
item_names = ["chalk", "cheese", "eggs", "ham"]

# Index:         1     2     3     4
item_prices = [2.30, 3.50, 4.25, 2.00]

println(item_names[1:2])

["chalk", "cheese"]

Let's practice!

Introduction to Julia