源：DataCamp

datacamp 的 DAILY PRACTICE + 日常收集。

List of lists

As a data scientist, you'll often be dealing with a lot of data, and it will make sense to group some of this data.

Instead of creating a flat list containing strings and floats, representing the names and areas of the rooms in your house, you can create a list of lists. The script on the right can already give you an idea.

Don't get confused here: "hallway" is a string, while hall is a variable that represents the float 11.25 you specified earlier.

# area variables (in square meters)

hall = 11.25

kit = 18.0

liv = 20.0

bed = 10.75

bath = 9.50

# house information as list of lists

house = [["hallway", hall],

         ["kitchen", kit],

         ["living room", liv],

         ["bedroom", bed],

         ["bathroom", bath]]

# Print out house

print(house)

# Print out the type of house

print(type(house))

Subset and conquer

一个元素毫无疑问也是一个子集，因此不论是取一段或者随机访问一个元素都叫做 subsetting

# Create the areas list

areas = ["hallway", 11.25, "kitchen", 18.0, "living room", 20.0, "bedroom", 10.75, "bathroom", 9.50]

# Print out second element from areas

print(areas[1])

# Print out last element from areas

print(areas[-1])

# Print out the area of the living room

print(areas[5])

#Subset and calculate

# Create the areas list

areas = ["hallway", 11.25, "kitchen", 18.0, "living room", 20.0, "bedroom", 10.75, "bathroom", 9.50]

# Sum of kitchen and bedroom area: eat_sleep_area

eat_sleep_area = areas[3] + areas[-3]

# Print the variable eat_sleep_area

print(eat_sleep_area)

Slicing and dicing

Selecting single values from a list is just one part of the story. It's also possible to slice your list, which means selecting multiple elements from your list. Use the following syntax:

my_list[start:end]

The start index will be included, while the end index is not.

# Create the areas list

areas = ["hallway", 11.25, "kitchen", 18.0, "living room", 20.0, "bedroom", 10.75, "bathroom", 9.50]

# Use slicing to create downstairs

downstairs = areas[0:6]

# Use slicing to create upstairs

upstairs = areas[6:10]

# Print out downstairs and upstairs

print(downstairs)

print(upstairs)

However, it's also possible not to specify these indexes. If you don't specify the begin index, Python figures out that you want to start your slice at the beginning of your list. If you don't specify the end index, the slice will go all the way to the last element of your list.

# Create the areas list

areas = ["hallway", 11.25, "kitchen", 18.0, "living room", 20.0, "bedroom", 10.75, "bathroom", 9.50]

# Alternative slicing to create downstairs

downstairs = areas[:6]

# Alternative slicing to create upstairs

upstairs = areas[6:]

List Manipulation

1、反向选就不用考虑 0 了，数到几就是几

2、如下操作也可以增加元素

In [3]: x

Out[3]: ['a', 'b', 's', 't']

In [4]: x[2:] = ["s", "t", "hi"]

In [5]: x

Out[5]: ['a', 'b', 's', 't', 'hi']

Extend a list

# Create the areas list and make some changes

areas = ["hallway", 11.25, "kitchen", 18.0, "chill zone", 20.0,

         "bedroom", 10.75, "bathroom", 10.50]

# Add poolhouse data to areas, new list is areas_1

areas_1 = areas + ["poolhouse", 24.5]

# Add garage data to areas_1, new list is areas_2

areas_2 = areas_1 + ["garage", 15.45]

Delete list elements

del(areas[-4:-2])

Inner workings of lists

Change the second command, that creates the variable areas_copy, such that areas_copy is an explicit copy of areas

# Create list areas

areas = [11.25, 18.0, 20.0, 10.75, 9.50]

# Create areas_copy

# areas_copy = areas

areas_copy = list(areas)

# Change areas_copy

areas_copy[0] = 5.0

# Print areas

print(areas)

areas_copy = areas[:] 也是可以的！

巴特西

Python笔记 #02# Inner workings of lists