Intro to Python for Data Science Learning 2

List

from:https://campus.datacamp.com/courses/intro-to-python-for-data-science/chapter-2-python-lists?ex=2

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• Create a list

As opposed to int, bool etc., a list is a compound data type; you can group values together:

a = "is"
b = "nice"
my_list = ["my", "list", a, b]

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• Create list with different types

A list can contain any Python type. Although it's not really common, a list can also contain a mix of Python types including strings, floats, booleans, etc.

# area variables (in square meters)
hall = 11.25
kit = 18.0
liv = 20.0
bed = 10.75
bath = 9.50

# Adapt list areas
areas = ["hallway",hall, "kitchen",kit, "living room", liv, "bedroom",bed, "bathroom", bath]

# Print areas
print(areas)

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•  Select the valid list

• my_list = [el1, el2, el3]

 both of them are correct:A. [1, 3, 4, 2] B. [[1, 2, 3], [4, 5, 7]] C. [1 + 2, "a" * 5, 3]

Subsetting lists

• Subset and conquer

x = ["a", "b", "c", "d"]
x[1]
x[-3] # same result!

• Subset and calculate

x = ["a", "b", "c", "d"]
print(x[1] + x[3])

•  

• Slicing and dicing

x = ["a", "b", "c", "d"]
x[1:3]

The elements with index 1 and 2 are included, while the element with index 3 is not.



• Slicing and dicing (2)

x = ["a", "b", "c", "d"]
x[:2]
x[2:]
x[:]

•  

• Subsetting lists of lists

x = [["a", "b", "c"],
     ["d", "e", "f"],
     ["g", "h", "i"]]
x[2][0]
x[2][:2]

List Manipulation

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Replace list elements

x = ["a", "b", "c", "d"]
x[1] = "r"
x[2:] = ["s", "t"]


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Extend a list

x = ["a", "b", "c", "d"]
y = x + ["e", "f"]

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Delete list elements

x = ["a", "b", "c", "d"]
del(x[1])

Pay attention here: as soon as you remove an element from a list, the indexes of the elements that come after the deleted element all change!
The ; sign is used to place commands on the same line. The following two code chunks are equivalent:

# Same line
command1; command2

# Separate lines
command1
command2

So if delete two items, pay more attention here. better to use like this del(areas[-4:-2]), instead of "del(areas[10]); del(areas[11])","del(areas[10:11])" "del(areas[-3]); del(areas[-4])",

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Inner workings of lists

 if use "areas_copy = areas", then they are the same thing, when value in one of them changed, both of them will be changed.

if use "areas_copy = areas[:]", then they are not the same thing, when value in one of them changed, the other one will Not be changed.