Python 如何检查 Pandas 中是否存在列
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How to check if a column exists in Pandas
提问by npires
Is there a way to check if a column exists in a Pandas DataFrame?
有没有办法检查 Pandas DataFrame 中是否存在列？
Suppose that I have the following DataFrame:
假设我有以下 DataFrame：
>>> import pandas as pd
>>> from random import randint
>>> df = pd.DataFrame({'A': [randint(1, 9) for x in xrange(10)],
'B': [randint(1, 9)*10 for x in xrange(10)],
'C': [randint(1, 9)*100 for x in xrange(10)]})
>>> df
A B C
0 3 40 100
1 6 30 200
2 7 70 800
3 3 50 200
4 7 50 400
5 4 10 400
6 3 70 500
7 8 30 200
8 3 40 800
9 6 60 200
and I want to calculate df['sum'] = df['A'] + df['C']
我想计算 df['sum'] = df['A'] + df['C']
But first I want to check if df['A']exists, and if not, I want to calculate df['sum'] = df['B'] + df['C']instead.
但首先我想检查是否df['A']存在，如果不存在，我想改为计算df['sum'] = df['B'] + df['C']。
采纳答案by chrisb
This will work:
这将起作用：
if 'A' in df:
But for clarity, I'd probably write it as:
但为了清楚起见，我可能会写成：
if 'A' in df.columns:
回答by C8H10N4O2
To check if one or morecolumns all exist, you can use set.issubset, as in:
要检查一列或多列是否都存在，您可以使用set.issubset，如下所示：
if set(['A','C']).issubset(df.columns):
df['sum'] = df['A'] + df['C']
As @brianpck points out in a comment, set([])can alternatively be constructed with curly braces,
正如@brianpck 在评论中指出的那样，set([])也可以用花括号构造，
if {'A', 'C'}.issubset(df.columns):
See this questionfor a discussion of the curly-braces syntax.
有关花括号语法的讨论，请参阅此问题。
Or, you can use a list comprehension, as in:
或者，您可以使用列表推导式，例如：
if all([item in df.columns for item in ['A','C']]):
回答by Gerges
Just to suggest another way without using if statements, you can use the get()method for DataFrames. For performing the sum based on the question:
只是为了建议不使用 if 语句的另一种方法，您可以使用s的get()方法DataFrame。根据问题执行求和：
df['sum'] = df.get('A', df['B']) + df['C']
The DataFrameget method has similar behavior as python dictionaries.
该DataFrameget方法也有类似的行为，Python字典。
