根据列表的第一个元素从主列表创建子列表

Question

I have the below List:

master_list =[['Apple','Red','Fresh','CA'],['Banana','Yellow','Fresh','NY'],['Mandarin','Orange','Fresh','WA'],['Apple','Red','Fresh','NJ'],['Banana','Yellow','Fresh','TX'],
['Apple','Red','Old','CA'],['Mandarin','Orange','Fresh','CA'],['Pineapple''Yellow','Fresh','MI']]

I need to loop through the above list and create separate lists based on the 0th element of each sublist in the master_list

The expected output is

l_apple=[['Apple','Red','Fresh','CA'],['Apple','Red','Fresh','NJ'],['Apple','Red','Old','CA']]
l_banana=[['Banana','Yellow','Fresh','TX'],['Banana','Yellow','Fresh','NY']]
l_mandarin=[['Mandarin','Orange','Fresh','WA'],['Mandarin','Orange','Fresh','CA']]
l_pineapple=[['Pineapple''Yellow','Fresh','MI']]"

i would really appreciate any suggestions or tips to code it in Python in an efficient manner.

Please note:We do not have a fixed list of fruits.So the number of lists that need to be generated might change based on the unique values(sourced from the first element of the list in the nested list) of fruits. Thanks in advance for the help

Answer 1

Since you have a dynamic number of fruits, you don't want to give each one a statically named variable. Something like a dict is a better option:

>>> from collections import defaultdict
>>> fruit_dict = defaultdict(list)
>>> for fruit in master_list:
...     fruit_dict[fruit[0]].append(fruit)
...
>>> dict(fruit_dict)
{
    'Apple': [['Apple', 'Red', 'Fresh', 'CA'], ['Apple', 'Red', 'Fresh', 'NJ'], ['Apple', 'Red', 'Old', 'CA']], 
    'Banana': [['Banana', 'Yellow', 'Fresh', 'NY'], ['Banana', 'Yellow', 'Fresh', 'TX']], 
    'Mandarin': [['Mandarin', 'Orange', 'Fresh', 'WA'], ['Mandarin', 'Orange', 'Fresh', 'CA']], 
    'PineappleYellow': [['PineappleYellow', 'Fresh', 'MI']]
}

Answer 2

As it was well said by Samwise, this is better approached by using a dictionary. But in case you really need to create those variables, and if you are at module scope , you can achieve this by doing the following:

master_list =[['Apple','Red','Fresh','CA'],['Banana','Yellow','Fresh','NY'],['Mandarin','Orange','Fresh','WA'],['Apple','Red','Fresh','NJ'],['Banana','Yellow','Fresh','TX'], ['Apple','Red','Old','CA'],['Mandarin','Orange','Fresh','CA'],['Pineapple','Yellow','Fresh','MI']]

for list_ in master_list:
    name = f'l_{list_[0].lower()}'
    vars().setdefault(name, []).append(list_)

outputs

>>> l_apple
[['Apple', 'Red', 'Fresh', 'CA'], ['Apple', 'Red', 'Fresh', 'NJ'], ['Apple', 'Red', 'Old', 'CA']]
>>> l_pineapple
[['Pineapple', 'Yellow', 'Fresh', 'MI']]
>>> l_mandarin
[['Mandarin', 'Orange', 'Fresh', 'WA'], ['Mandarin', 'Orange', 'Fresh', 'CA']]
>>> l_banana
[['Banana', 'Yellow', 'Fresh', 'NY'], ['Banana', 'Yellow', 'Fresh', 'TX']]