Getting a list out of nested list in python-CodePudding

I am getting list out of a nested list.

list_of_data = [{'id':99,
                 'rocketship':{'price':[10, 10, 10, 10, 10], 
                               'ytd':[1, 1, 1.05, 1.1, 1.18]}},
                {'id':898,
                 'rocketship':{'price':[10, 10, 10, 10, 10], 
                               'ytd':[1, 1, 1.05, 1.1, 1.18]}},
                {'id':903,
                 'rocketship':{'price':[20, 20, 20, 10, 10], 
                               'ytd':[1, 1, 1.05, 1.1, 1.18]}},
                {'id':999,
                 'rocketship':{'price':[20, 20, 20, 10, 10], 
                               'ytd':[1, 3, 4.05, 1.1, 1.18]}},
                ]

price, ytd = map(list, zip(*((list_of_data[i]['rocketship']['price'], list_of_data[i]['rocketship']['ytd']) for i in range(0, len(list_of_data)))))

My expected output is below (But, I am getting something different):

price = [10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 20, 20, 20, 10, 10, 20, 20, 20, 10, 10]

ytd = [1, 1, 1.05, 1.1, 1.18, 1, 1, 1.05, 1.1, 1.18, 1, 1, 1.05, 1.1, 1.18, 1, 3, 4.05, 1.1, 1.18]

But, I am getting this:
price
Out[19]: 
[[10, 10, 10, 10, 10],
 [10, 10, 10, 10, 10],
 [20, 20, 20, 10, 10],
 [20, 20, 20, 10, 10]]

Expected output:

price = [10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 20, 20, 20, 10, 10, 20, 20, 20, 10, 10]

ytd = [1, 1, 1.05, 1.1, 1.18, 1, 1, 1.05, 1.1, 1.18, 1, 1, 1.05, 1.1, 1.18, 1, 3, 4.05, 1.1, 1.18]

CodePudding user response：

I traded a bit of readability for performance here

import itertools

tuples = ((item['rocketship']['price'], item['rocketship']['ytd']) for item in list_of_data)
price, ytd = functools.reduce(lambda a, b: (a[0]   b[0], a[1]   b[1]), tuples, ([], []))

I tried to keep things in a single loop and use generator to optimize memory use. But if the data is big, the resulting price and ytd are also big too, hopefully you thought about that already.

CodePudding user response：

try this:

list_of_data = [{'id': 99,
             'rocketship': {'price': [10, 10, 10, 10, 10],
                            'ytd': [1, 1, 1.05, 1.1, 1.18]}},
            {'id': 898,
             'rocketship': {'price': [10, 10, 10, 10, 10],
                            'ytd': [1, 1, 1.05, 1.1, 1.18]}},
            {'id': 903,
             'rocketship': {'price': [20, 20, 20, 10, 10],
                            'ytd': [1, 1, 1.05, 1.1, 1.18]}},
            {'id': 999,
             'rocketship': {'price': [20, 20, 20, 10, 10],
                            'ytd': [1, 3, 4.05, 1.1, 1.18]}},
            ]
price = []
ytd = []
for i in list_of_data:
    price.extend(i.get('rocketship').get('price'))
    ytd.extend(i.get('rocketship').get('ytd'))
print(price)
print(ytd)

>>> [10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 20, 20, 20, 10, 10, 20, 20, 20, 10, 10]
>>> [1, 1, 1.05, 1.1, 1.18, 1, 1, 1.05, 1.1, 1.18, 1, 1, 1.05, 1.1, 1.18, 1, 3, 4.05, 1.1, 1.18]

CodePudding user response：

Perform a list comprehension and flatten your result.

ytd = sum([d['rocketship']['ytd'] for d in list_of_data], [])
price = sum([d['rocketship']['price'] for d in list_of_data], [])

CodePudding user response：

Using list comprehension:

price, ytd = [i for item in list_of_data for i in item["rocketship"]["price"]],
             [i for item in list_of_data for i in item["rocketship"]["ytd"]]

Output

price: [10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 20, 20, 20, 10, 10, 20, 20, 20, 10, 10] 

ytd: [1, 1, 1.05, 1.1, 1.18, 1, 1, 1.05, 1.1, 1.18, 1, 1, 1.05, 1.1, 1.18, 1, 3, 4.05, 1.1, 1.18]

CodePudding user response：

I try to use a double comprehension. I don't know it's a good idea as it could hurt code readibility, maybe.

price = [
    item
    for sublist in [rocket["rocketship"]["price"] for rocket in list_of_data]
    for item in sublist
]

ytd = [
    item
    for sublist in [rocket["rocketship"]["ytd"] for rocket in list_of_data]
    for item in sublist
]

print(price)
print(ytd)