如何从CSV的键标题下的字典中将列表值写入列

Question

我正在尝试从字典中创建一个csv文件，其中每个值都是一个数字列表。

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我希望csv像这样：

example = {"A" : [1,2,3], "B" : [1], "C": [4,5,6,7,8,9]}

我尝试做类似的事情：

A,B,C
1,1,4
2, ,5
3, ,6
 , ,7
 , ,8
 , ,9

但是最终在excel中出现了这样的情况：

with open("example.csv", "w", newline='') as f:
    headers = example.keys()
    writer = csv.DictWriter(f, fieldnames=headers)
    writer.writeheader()
    writer.writerow(example)

我可以考虑做的一些可能的事情是在较小的列表值上添加一个空格，使其与最长的列表值具有相同的长度，然后基于索引值进行zip，然后将每个元组都排成一行。如果我以这种方式这样做，是否会找到一种有效的方法来找到最大的列表大小并在没有很多for循环和附加的情况下附加空白？列表大小可以达到65000。此外，字典中的条目数是可变的，这意味着它永远不会设置常量。

Answer 1

仅带有标准库（假设python 3.7+-用于保留标头中键的正确顺序所必需的dict的顺序保留功能）

import csv
from itertools import zip_longest

example = {"A" : [1,2,3], "B" : [1], "C": [4,5,6,7,8,9]}
keys, values = zip(*example.items())
data = (dict(zip(keys, row)) for row in zip_longest(*values, fillvalue=''))
with open('output.csv', 'w') as f:
    wrtr = csv.DictWriter(f, fieldnames=keys)
    wrtr.writeheader()
    wrtr.writerows(data)

编辑：对于3.7 *之前的python版本，您不能依赖保留顺序，因此您需要按所需顺序显式提供标头（即，它不能来自dict.keys（））

import csv
from itertools import zip_longest

header = ['A', 'B', 'C']
example = {"A" : [1,2,3], "B" : [1], "C": [4,5,6,7,8,9]}

values = (example.get(key, []) for key in header)
data = (dict(zip(header, row)) for row in zip_longest(*values, fillvalue=''))
with open('output.csv', 'w') as f:
    wrtr = csv.DictWriter(f, fieldnames=header)
    wrtr.writeheader()
    wrtr.writerows(data)

• 3.6保留订单功能中的内容被认为是实现细节，因此不应依赖。

Answer 2

如果您可以使用pandas库，请尝试以下操作，

import pandas as pd

example = {"A" : [1,2,3], "B" : [1], "C": [4,5,6,7,8,9]}
df = pd.DataFrame({ key:pd.Series(value) for key, value in example.items() })
df.to_csv('example_dict.csv', index=False)

Answer 3

解决方案之一是将字典转换为数据帧，然后将其用于csv文件，但是请记住，仍然没有办法为非等长数组赋空白值，它将是NaN。

import pandas as pd 
df = pd.DataFrame.from_dict(example, orient='index') 
df = df.T           # Transpose dataframe to get same orientation as required

Answer 4

尝试一下：

import csv
from itertools import zip_longest
example = {"A" : [1,2,3], "B" : [1], "C": [4,5,6,7,8,9]}

v = list(zip_longest(example['A'], example['B'], example['C'], fillvalue=' '))
print(v)

with open("example.csv", "w", newline='') as f:
    headers = example.keys()
    writer = csv.DictWriter(f, fieldnames=headers)
    writer.writeheader()

    for row in v:
        d = {header:value for header, value in zip(headers, row)}
        writer.writerow(d)

example.csv输出：

A,B,C
1,1,4
2, ,5
3, ,6
 , ,7
 , ,8
 , ,9