Python-修改一个csv文件 [英] Python- Modifying a csv file

问题描述

现在，我知道在读取csv文件时通常不可行，因此您需要创建一个新的csv文件并对其进行写入.我遇到的问题是保留数据的原始顺序.

Now I know it's usually not feasible to modify a csv file as you are reading from it so you need to create a new csv file and write to it. The problem I'm having is preserving the original order of the data.

输入的csv文件如下所示:

The input csv file looks like follows:

C1       C2         C3
apple    BANANA     Mango
pear     PineApple  StRaWbeRRy

我想将所有数据转换为小写并输出一个新的csv文件，如下所示:

I want to turn all the data into lower case and output a new csv file that looks like:

C1       C2         C3
apple    banana     mango
pear     pineapple  strawberry

到目前为止，我可以遍历输入的csv文件并将所有值都转换为小写，但是我不知道如何将其重新写成该格式的csv文件.我的代码是:

So far I can iterate through the input csv file and turn all the values into lower case but I don't know how to rewrite it back into a csv file in that format. The code I have is:

def clean (input)
  aList = []
  file = open(input, "r")
  reader = csv.reader(file, delimiter = ',')
  next(reader, None) # Skip the header but I want to preserve it in the output csv file
  for row in reader:
     for col in row:
        aList.append(col.lower())

所以现在我有了一个包含所有小写数据的列表，如何将其重写回与输入相同格式(行和列数相同)的csv文件中，包括我在代码中跳过的标题行

So now I have a list with all the lowercase data, how do I rewrite it back into a csv file of the same format (same number of rows and columns) as the input including the header row that I skipped in the code.

推荐答案

熊猫方式:

使用 pandas 读取文件并获取数据框.然后，您可以简单地使用 lower()

Read the file using pandas and get the dataframe. Then you can simply use lower()

import pandas as pd

def conversion(text):
    return text.lower()
    

df = pd.read_csv(file_path)
df[column_name] = df[column_name].map(conversion)

甚至是一个班轮:

df[column_name] = df[column_name].apply(lambda x: x.lower()) # If you have nan or other non-string values, you may need to convert x to string first like str(x).lower()

然后，您可以使用 to_csv 函数

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