Vanilla Flashcards
what native class method can you call to convert the object to a float?
.to_f
what type of quotes can be used for string interpolation ?
only double quotes, normally double or single can be used to create a string
describe and name all the methods to add and remove elements to the beginning and end of an Array
push/pop will add/remove from the end of an Array
shift/unshift will remove/add from the beginning of an Array
what Array method can we use to remove duplicates?
Array.uniq
what native class method can you call to convert the object to a string?
to_s
e.g. [1] pry(main)> 40.to_s => “40” [2] pry(main)> 40 => 40
how do we create or use a range in Ruby?
(1..5) or (1…5) create a range that can be iterated over in a for loop with the items 1 to 5 inclusive and 1 to 4 inclusive respectively
we can also create an array out of them by doing (1..5).to_a
can you access a variable created in a while loop from outside that loop?
no, it must be declared before going into the while loop if you want to do so. otherwise it is confined to the scope of that while loop
how create blocks of comments?
=begin
kjsanfafdjsankfnkdjkjndfsa
=end
how can we create a method that mutates a variable? (modifies in place)
with the .replace method. this will only work on string and arrays though, integers for example are too primative to be worked with in this way as they don’t store state (note the bang! isn’t required, but probably good practice
e.g.
def lev_pop!(array)
new_array = []
removed = array[-1]
array.each_with_index {
|element, i|
if i != array.length - 1
new_array.push(element)
end
}
array.replace(new_array)
return removed
end
array = (“a”..”f”).to_a
popped_elements = lev_pop!(array)
popped_array = array
p popped_elements
p popped_array
terminal:
“f”
[“a”, “b”, “c”, “d”, “e”]
how to remove letters from a String?
String.slice, the argument is the index for the letter (if it was an array), can use ranges and negatives as well. it will return what was removed. slice! will also modify the String in place, leaving the “left over” letters
[248] pry(main)> test = “string”
=> “string”
[249] pry(main)> test.slice(0)
=> “s”
[250] pry(main)> test.slice(1)
=> “t”
[251] pry(main)> test.slice(1..3)
=> “tri”
[252] pry(main)> test.slice(-1)
=> “g”
[253] pry(main)> test.slice(-2..-1)
=> “ng”
what is a class constructor and how do we use it?
a class contructor is used to instantiate a class into and object.
when we (or Ruby) define the class, there is a constructor method that must be called initialize, initialize is a reserved word. in here we define attributes and any arguments required to instantiate.
in order to create an object of class Foobar, we write: some\_object = Foobar.new()
how does the <=> aka spaceship operator work?
also generally what can it be useful for?
a <=> b :=
if a < b then return -1
if a = b then return 0
if a > b then return 1
if a and b are not comparable then return nil
it is useful for sorting an array
how do we print to terminal in ruby code
puts e.g. puts 1+1
what are the rules of thumb for where to put exception handling?
rule of thumb for where to put exception handling:
- anywhere that requires user input where they can input something that your code cannot accept or support or do anything with
- anything that uses some sort of database where a value or the class of the value could potentially be something unsupported or left blank etc
- anything using APIs to return results and anything using those results
- anything attempting internet/network communication
native type method to remove trailing and leading white space?
native type method to remove only trailing white space?
String.strip
and
String.chomp
describe the gotchya when using ARGV and there is a gets in your script
gets must be changed to STDN.gets
what is another name for instance variable?
attribute
how do we make an instance variable and how does it work?
putting an @ infront of the variable and it is accessable instance wide (each of object of that calss has it’s own independent @variable
how access an index of an array where you know the contents but not the index value?
four_letter_animals[four_letter_animals.index(“elephant”)]
what is an easy way in ruby to create a break point ?
add the line binding.pry (must require ‘pry’) first
you can check what values a variable is at this break point by simply typing in it’s name
e.g.
require ‘pry’
x = 0
until x == 5
p x
x += 1
binding.pry
y = 0
end
how does Array.pop work?
pop with remove the last (or more with an integer argument) element of an array in place.
it will also return all the popped elements in an array
describe how we can use instance variables
an instance variable has class scope
it cannot be used as a paremeter for a method in the class, but it can be passed as an argument to the method
can you string together ruby methods?
yes
e.g.
some_string.reverse.downcase
what Array method can we use to concatonate an array of strings and create a single string?
.join
e.g.
array_of_strings.join
what is the inverse of #reject?
#select
what does the gets method stand for and do
GET String, waits for user input
what is another name for attribute?
instance variable
what is ARGV
it is an argument that can be given at runtime via the command line running the script.
it can be accessed with ARGV[0], ARGV[1], etc
e.g.
ruby some_script -t
where in some_script, there is a conditional somewhere that executes if ARGV[0] == “-t”
in what scenario would we definetly want to use Array.each to iterate rather than for item in array?
when we want to also receive the iterations index
in ruby what is truthy and what is falsey?
literallyt everything that is no false or nil is truthy, even the integer 0 is truthy
what is a String class method that can replace all occurances of one string with another?
.gsub (as in Global Substitute)
e. g.
poem. gsub(“toast”, “honey”)
what native class method can you call to convert the object to a array?
what native class method can you call to convert the object to a integer?
to_i
how do we run a command in the terminal using ruby
em { background-color: lightgray; padding: 10px; border-radius: 10px; }
put the command in a backtick e.g.
touch example.txt
or
touch #{var_name}.txt
before doing anything with an any enumerable, what should be the first step?
go to the documentation for enumerable and then the type of enumerable, e.g. array, range, hash, etc and see if it can be done via one of those methods first.
how do we allow an instance method to be chainable?
by using
return self
what is the result of “some string”.to_i ?
0
how can we pass in and use an operator in a method?
we can use symbols and the .send method
e.g.
def arithmetic(num0, num1, operator)
result = num0.to_f.send(operator, num1.to_f)
return result
end
p arithmetic(1, 2, :+)
p arithmetic(4, 2, “-“)
p arithmetic(6, 4, :*)
p arithmetic(7, 3, “/”)
how do you do less than and greater then in a case statement?
you can’t, you have to use a range
e.g.
case distance
when (0…10)
puts “long way to go but you’re doing amazing!”
when (10…20)
puts “almost halfway now, killing it!”
when (20…30)
puts “now for the final push, keep going!”
when (30…40)
puts “sprint!!!!”
end
ruby naming convention?
name_variables_with_snake_case
ClassesUseCapitalCamelCase
what does the .each method return?
it returns the original array, it does not return a modified array or anything at all in the block statement
how to print a block of text in ruby?
print “””
somet text
some more
blah blah bhlah
“””
map_with_index doesn’t exist as a core method, so what is the easy work around?
map.with_index
hash keys can be defined in what way to save memory?
using symbols, like so
some_hash = {
symb: value
}
reference_a_hash = some_hash[:symb]
as opposed to
some_hash = {
“string_key” => value
23 => value
}
reference_a_hash = some_hash[“string_key”]
reference_a_hash = some_hash[23]
what do you call the equivalent of a dictionary in Ruby?
a Hash
difference between String.chomp and String.strip?
chomp gets rid of whitespace at the end, strip gets rid of leading and trailing white space
do ruby methods need a return statement?
no. they will automatically return the last statement in the method if no return is provided
How do we represent infinity in ruby?
-Float::INFINITY
and
Float::INFINITY
what class does every class created by Ruby or a user inherit from?
the Object class
what is a deep copy and how can we avoid them if desired?
a deep copy is when one variable is assigned to another, and then modifying one of those variables also modifies the other.
most common example is with arrays
[114] pry(main)> a = (0…10).to_a
=> [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
[115] pry(main)> b = a
=> [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
[116] pry(main)> a.pop
=> 9
[117] pry(main)> a
=> [0, 1, 2, 3, 4, 5, 6, 7, 8]
[118] pry(main)> b
=> [0, 1, 2, 3, 4, 5, 6, 7, 8]
we can avoid this with the .dup method:
[119] pry(main)> a = (0…10).to_a
=> [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
[120] pry(main)> b = a.dup
=> [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
[121] pry(main)> b
=> [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
[122] pry(main)> a.pop
=> 9
[123] pry(main)> a
=> [0, 1, 2, 3, 4, 5, 6, 7, 8]
[124] pry(main)> b
=> [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
[125] pry(main)>
difference between p, puts, print
p and puts includes a new line character, print does not.
p prints the “quotes”, good for debugging so it is clear if something is a string or not (example an integer)
how do we make a class variable and how does it work?
using @@ syntax
this variable is shared across all instances of the class, the value is the same across all sintances and changing the value in on instance changes it in all the others
what is a Hash in ruby?
it is like a dictionary
what do methods with a ! or an ? at the end do?
? simply indicates that a true or false will be returned
! indicates that this is a “dangerous method”, basically it will modify the object it is called on, instead of simply outputing a result of the method being called on the object
when doing a begin and rescue, what is the difference between using p and puts for the error?
puts will just give the contents of the raise statement as defined by the script
p will give you the full error type and message generated by ruby
what expression can you use as a shortcut for .push on an Array?
<<
inside #{} what can be written?
any ruby code at all, it will be executed and whatever it returns is printed as a string where the #{} was
what is the inverse of #select?
#reject
How do you work with the Hash#each block?
meals = {
breakfast: “oats”,
lunch: “curry”,
dinner: “ramen”
}
meals.each do |key, value|
puts value
end
how can you do an each over just a range of indexes?
just put a range in the index like so:
start_index = train_line.stops.find_index { |stop| stop[:name] == station_start }
finish_index = train_line.stops.find_index { |stop| stop[:name] == station_finish }
stops = []
train_line.stops[start_index..finish_index].each do |stop|
stops << stop[:name]
end
what does This::Syntax mean?
e. g.
* robot = ToyRobot::Robot.new*
it the Syntax class from the This module
e.g.
*module ToyRobot class Robot attr\_reader :north, :east, :facing*
def initialize(north = 0, east = 0, facing = “north”)
@north = north
@east = east
@facing = facing
end
- . . .*
- . . .*
- . . .*
