05-Lists

Lists

• are data structures to store other different data type collections
• there are a whole lot of methods for lists

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List Methods

• append - inserts a new item at the end
• extend - inserts the given items(or a new list) at the end and extends the original one
• insert - inserts an item at the specified index
• clear - removes all the items from the list
• pop - removes and returns an item from the given index (by default removes from the last)
• remove(x) - removes the first instance of the given item
• index(x) - returns the index of the specified item
• count - returns how many times an item occurs in a list
• reverse - reverses the list w/o creating a new one
• sort - sorts item based on asc order
• join - technically a string method but is used to combine/concatenate items of a list

  words = ["Coding", "is", "fun!"]
  text = " ".join(words) # joins the words with a space
  print(text)

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List Comprehension

• does a specific task for every iteration when looping over a list and it creates a new list

  nums = [1, 2, 3]
  # create a new list where the items are doubles
  doubled_nums = [num*2  for num in nums]
  print(doubled_nums)

• technically, we can do the same using loops but that'd be a bit tedious
• used a lot with data science, web deb, etc.

LS with Conditional Logic

numbers = [1,2,3,4,5,6]

# store even values
evens = [num for num in numbers if num % 2 == 0] # [2,4,6]

# if even, double it and if odd, half it
weird = [num*2 if num%2==0 else num/2 for num in numbers] # [.5, 4, 1.5, 8, 2.5, 12]

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Nested Lists

• lists inside lists

• used a lot in almost all of the fields

  nested_list = [[1,2,3], [4,5,6], [7,8,9]]
  
  print(nested_list[0][1]) #2
  print(nested_list[1][-1]) #6
  

• we'll have to use nested loops to iterate over these

• List Comprehension in Nested Loop

  empty_board = [['x' for x in range(1,4)] for n in range(1,4)]
  print(empty_board)