Python

Question

我希望更精通列表理解的人可以提供一些建议。

考虑以下数据集：

Onions,copper,manganese,magnesium,phosphorus
Tomatoes,copper,manganese,potassium
Garlic,manganese
Celery,manganese,potassium,sodium,salt
Bell Peppers,copper,manganese
Butter,sodium,salt
Eggplant,copper,manganese
Grapes,copper,manganese,potassium

我需要制定一个字典，其中键是矿物质，值是一组含有该矿物质的食物-像这样：

{'copper': {'Tomatoes', 'Onions', 'Bell Peppers', 'Eggplant'}, 'maganeese': {'Onions', 'Tomatoes', 'Garlic', 'Celery', 'Bell Peppers', 'Eggplant', 'Grapes'}...  etc.}

您会注意到食物位于第一个位置，其次是它所含的矿物质。

我想我可能需要将食物和矿物质分成两个列表，食物列表和矿物质列表。从逻辑上讲，我完全不知道如何完成这项任务。

with open ('file.txt', 'r') as fp:
    D = dict()
    food_list = []
    mineral_list = []
    for line in fp:
        line = line.strip().split(",")
        line = [x for x in line if x]
        food_list.append(line[0])
    print(food_list)

有人可以在这里提供正确方向的推动吗？

Answer 1

你可以这样做：

import pprint

mineral_table = {}
with open("ip.txt") as infile:
    for line in infile:
        # split the line into vegetable and minerals
        vegetable, *minerals = line.strip().split(',')

        # for each mineral add the vegetable to the mineral list
        for mineral in minerals:
            mineral_table.setdefault(mineral, []).append(vegetable)

pprint.pprint(mineral_table)

输出

{'copper': ['Onions', 'Tomatoes', 'Bell Peppers'],
 'magnesium': ['Onions'],
 'manganese': ['Onions', 'Tomatoes', 'Garlic', 'Celery', 'Bell Peppers'],
 'phosphorus': ['Onions'],
 'potassium': ['Tomatoes', 'Celery'],
 'salt': ['Celery'],
 'sodium': ['Celery']}

行：

# split the line into vegetable and minerals
vegetable, *minerals = line.strip().split(',')

使用 extended iterable unpacking. The for loop uses setdefault，来自文档：

If key is in the dictionary, return its value. If not, insert key with a value of default and return default. default defaults to None.

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