Python/Pandas:从列表中的字符串匹配中删除数据框中的行 [英] Python/Pandas: Drop rows from data frame on string match from list

问题描述

我有一个联系信息的.csv文件，我将其导入为熊猫数据框.

I have a .csv file of contact information that I import as a pandas data frame.

>>> import pandas as pd
>>> 
>>> df = pd.read_csv('data.csv')
>>> df.head()

  fName   lName                    email   title
0  John   Smith         [e-mail]     CEO
1   Joe   Schmo      [e-mail]  Bagger
2  Some  Person  [e-mail]   Clerk

导入数据后，我想删除其中一个字段包含列表中多个子字符串之一的行.例如:

After importing the data, I'd like to drop rows where one field contains one of several substrings in a list. For example:

to_drop = ['Clerk', 'Bagger']

for i in range(len(df)):
    for k in range(len(to_drop)):
        if to_drop[k] in df.title[i]:
            # some code to drop the rows from the data frame

df.to_csv("results.csv")

在Pandas中执行此操作的首选方法是什么?这是否应该是一个后处理步骤，还是最好先将其过滤后再写入数据帧?我的想法是，一旦在数据框对象中操作起来会更容易.

What is the preferred way to do this in Pandas? Should this even be a post-processing step, or is it preferred to filter this prior to writing to the data frame in the first place? My thought was that this would be easier to manipulate once in a data frame object.

推荐答案

使用

Use isin and pass your list of terms to search for you can then negate the boolean mask using ~ and this will filter out those rows:

In [6]:

to_drop = ['Clerk', 'Bagger']
df[~df['title'].isin(to_drop)]
Out[6]:
  fName  lName             email title
0  John  Smith  [e-mail]   CEO

另一种方法是加入术语，使其成为正则表达式，并使用矢量化的

Another method is to join the terms so it becomes a regex and use the vectorised str.contains:

In [8]:

df[~df['title'].str.contains('|'.join(to_drop))]
Out[8]:
  fName  lName             email title
0  John  Smith  [e-mail]   CEO

IMO，作为后处理步骤执行过滤将更加容易，并且可能更快，因为如果您决定在读取时进行过滤，那么您将迭代地增加效率不高的数据帧.

IMO it will be easier and probably faster to perform the filtering as a post processing step because if you decide to filter whilst reading then you are iteratively growing the dataframe which is not efficient.

或者，您可以分块读取csv，过滤掉不需要的行，然后将这些块附加到输出csv中

Alternatively you can read the csv in chunks, filter out the rows you don't want and append the chunks to your output csv

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