Python：在 for 循环中和 out 中添加到列表列表

Question

I want to create a new list with the 0-indexed value outside a for loop, then add to that same list using a for loop. My toy example is:

import random

data = ['t1', 't2', 't3']

masterlist = [['col1', 'animal1', 'animal2', 'animal3']]
animals = ['cat', 'dog', 'chinchilla']

for item in data:
    masterlist.append([item])
    for animal in animals:
        number1 = random.randint(1, 100)
        number2 = random.randint(1, 100)
        masterlist.append([str(number1) + ',' + str(number2)])

masterlist  

but this outputs:

[['col1', 'animal1', 'animal2', 'animal3'],
 ['t1'],
 ['52,69'],
 ['8,77'],
 ['75,66'],
 ['t2'],
 ['67,33'],
 ['85,60'],
 ['98,12'],
 ['t3'],
 ['60,34'],
 ['25,27'],
 ['100,25']]

My desired output is:

[['col1', 'animal1', 'animal2', 'animal3'],
 ['t1', '52,69', '8,77', '75,66'], 
 ['t2', '67,33', '85,60', '98,12'],
 ['t3', '60,34', '25,27', '100,25']]

Answer 1

What about this solution which refactors your code a bit?

Solution 1

import random

data = ['t1', 't2', 't3']

masterlist = [['col1', 'animal1', 'animal2', 'animal3']]
animals = ['cat', 'dog', 'chinchilla']

for item in data:
    rv = []
    rv.append(item)
    for animal in animals:
        number1 = random.randint(1, 100)
        number2 = random.randint(1, 100)
        rv.append(str(number1) + ',' + str(number2))
    masterlist.append(rv)

Output:

>>> masterlist
[['col1', 'animal1', 'animal2', 'animal3'],
 ['t1', '88,43', '85,62', '84,21'],
 ['t2', '44,99', '32,54', '83,50'],
 ['t3', '82,87', '90,83', '91,84']]

Alternatively, the following would give the same result.

Solution 2

import random

data = ['t1', 't2', 't3']

masterlist = [['col1', 'animal1', 'animal2', 'animal3']]
animals = ['cat', 'dog', 'chinchilla']

for item in data:
    masterlist.append([item] + [f"{random.randint(1, 100)},{random.randint(1, 100)}" for animal in animals])

Answer 2

You can do something like this. Use a temp list to store items of each iteration. Moreover you were using to many square brackets while appending, this caused the too nested list.

import random

data = ['t1', 't2', 't3']

masterlist = [['col1', 'animal1', 'animal2', 'animal3']]
animals = ['cat', 'dog', 'chinchilla']

for item in data:
    temp = []
    temp.append(item)
    for animal in animals:
        number1 = random.randint(1, 100)
        number2 = random.randint(1, 100)
        temp.append(str(number1) + ',' + str(number2))
    masterlist.append(temp)

print(masterlist)

Answer 3

You can also use list comprehension as follows:

import random

data = ['t1', 't2', 't3']

masterlist = [['col1', 'animal1', 'animal2', 'animal3']]
animals = ['cat', 'dog', 'chinchilla']

for d in data:
     rv = [d] + [str(random.randint(1, 100)) + ',' + str(random.randint(1, 100)) for a in animals]

masterlist.append(rv)

Or even more hardcore in a single list comprehension:

masterlist+= [[d] + [str(random.randint(1, 100)) + ',' + str(random.randint(1, 100)) for a in animals] for d in data]