array.py

# Arrays (called lists in python)
arr = [1, 2, 3]
print(arr)

# Can be used as a stack
arr.append(4)
arr.append(5)
print(arr)

arr.pop()
print(arr)

arr.insert(1, 7)
print(arr)

arr[0] = 0
arr[3] = 0
print(arr)

# Initialize arr of size n with default value of 1
n = 5
arr = [1] * n
print(arr)
print(len(arr))

# Careful: -1 is not out of bounds, it's the last value
arr = [1, 2, 3]
print(arr[-1])

# Indexing -2 is the second to last value, etc.
print(arr[-2])

# Sublists (aka slicing)
arr = [1, 2, 3, 4]
print(arr[1:3])

# Similar to for-loop ranges, last index is non-inclusive
print(arr[0:4])

# But no out of bounds error
print(arr[0:10])

# Unpacking
a, b, c = [1, 2, 3]
print(a, b, c)

# Be careful though
# a, b = [1, 2, 3]

# Loop through arrays
nums = [1, 2, 3]

# Using index
for i in range(len(nums)):
    print(nums[i])

# Without index
for n in nums:
    print(n)

# With index and value
for i, n in enumerate(nums):
    print(i, n)

# Loop through multiple arrays simultaneously with unpacking
nums1 = [1, 3, 5]
nums2 = [2, 4, 6]
for n1, n2 in zip(nums1, nums2):
    print(n1, n2)

# Reverse
nums = [1, 2, 3]
nums.reverse()
print(nums)

# Sorting
arr = [5, 4, 7, 3, 8]
arr.sort()
print(arr)

arr.sort(reverse=True)
print(arr)

arr = ["bob", "alice", "jane", "doe"]
arr.sort()
print(arr)

# Custom sort (by length of string)
arr.sort(key=lambda x: len(x))
print(arr)


# List comprehension
arr = [i for i in range(5)]
print(arr)

# 2-D lists / Matrix
# creating 4 unique rows
arr = [[0] * 4 for i in range(4)]
print(arr)
print(arr[0][0], arr[3][3])

# This won't work
# arr = [[0] * 4] * 4

# 3 (row) * 4 (col) matrix 
mat = [[0] * 4 for row in range(3)]
print(mat)