Staff Learn To Code // Chapter #1 - The Basics

01_intro_data_structures.rb

# NOTE: 
# for basic data structures such as strings, boolean and integers, 
# please have a look at week 1 day 2 lecture notes

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# ARRAYS: lists of things

# an array of names
names = ["Faisal", "Sara", "Jane"]

# an array of arrays
xy_data_points = [[1, 2], [2, 3], [3,4]]

# an array of mixed data types
mixed = [true, 45, "just a string"]

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# HASHES: key, value pairs

# hashes are great for representing objects that have attributes (referred to as `keys`) that have values
person_1 = {
	name: "Jane Doe",
	age: 32
}

# Each key (attribute) of a hash has a value which could be any data type
person_2 = {
	name: "John Doe",
	age: 24,
	hobbies: ["Tennis", "Soccer", "Basketball"] # notice how the value here is an array
}

person_3 = {
	name: "John Doe",
	age: 24,
	meta_data: { # notice how the value is a hash
		data_of_birth: "1992-01-01"
	}
}

02_reading_data.rb

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# ARRAYS

# let's say we have an array of names (where each name is a string)
names = ["Faisal", "Sara", "Jane"]

# arrays are 0 indexed, which means the index of the first item is 0
puts names[1] # prints "Sara" to the terminal

# in ruby, trying to access an array position that doesn't exist return nil
# may give you an error in other languages
puts names[500] # prints nil or nothing to the terminal

# to get the last item of an array without knowing the length
puts names[-1] # using -1 as index with automatically map to the last index in the array

# arrays come with methods defined by ruby out of the box
puts names.length # returns the number of items in an array

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# HASHES

# let's say we have a hash to represent a person
john = {
	name: "John Doe",
	age: 24,
	hobbies: ["Tennis", "Soccer", "Basketball"]
}

# if we need to access a specific property of a hash, we do it as follows
puts john[:name] # prints "John Doe" to the terminal
puts john[:hobbies] # prints the list of hobbies inside of our object

# we can also chain our accessors, ex: getting the first hobby in the hobbies list
puts john[:hobbies][0] # prints "Tennis" to the terminal

03_storing_data.rb

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# STORING DATA IN ARRAYS

# let's say we have an array of names (where each name is a string)
names = ["Faisal", "Sara", "Jane"]

# if we want to add more names to our array, we do it as follows:
names << "Vicky"
names << "Norman"
puts names # outputs a list of 5 names (including the 2 we added)

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# STORING DATA IN HASHES

# let's say we have a hash to represent a person
jane = {
	name: "Jane Doe",
	age: 32
}

# we can add another attribute to this hash, ex: if we want to add hobbies to this person
jane[:hobbies] = ["Basketball", "Painting"]
jane[:favourite_fruit] = "Orange"
puts jane # prints the jane object along with the new attributes (keys) we added along with their values

04_symbols_vs_strings.md

What are the differences between Symbols & Strings?

1. Symbols' values remain the same / constant (Technical Term: 'Immutable', we can say symbols are immutable).
2. Multiple uses of the same symbol have uses the same amount of memory (no new copies, single copy per symbol)
3. (For Future Ref. // Not discussed yet) You can't call any of the String methods like #upcase, #split on Symbols.