如何检查 Pandas 中是否存在列

Question

How do I check if a column exists in a Pandas DataFrame df ?

   A   B    C
0  3  40  100
1  6  30  200

How would I check if the column "A" exists in the above DataFrame so that I can compute:

df['sum'] = df['A'] + df['C']

And if "A" doesn't exist:

df['sum'] = df['B'] + df['C']

Answer 1

This will work:

if 'A' in df:

But for clarity, I'd probably write it as:

if 'A' in df.columns:

Answer 2

To check if one or more columns all exist, you can use set.issubset , as in:

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,

if {'A', 'C'}.issubset(df.columns):

See this question for a discussion of the curly-braces syntax.

Or, you can use a generator comprehension, as in:

if all(item in df.columns for item in ['A','C']):

Answer 3

Just to suggest another way without using if statements, you can use the get() method for DataFrame s. For performing the sum based on the question:

df['sum'] = df.get('A', df['B']) + df['C']

The DataFrame get method has similar behavior as python dictionaries.

Answer 4

You can use the set's method issuperset :

set(df).issuperset(['A', 'B'])
# set(df.columns).issuperset(['A', 'B'])

Answer 5

You can also call isin() on the columns to check if it exists and call any() on the result to reduce it to a single boolean value ¹ :

if df.columns.isin(['A', 'C']).any():
    # do something

To check if a column name is not present, you can use the not operator in the if-clause:

if 'A' not in df:
    # do something

or along with the isin().any() call.

if not df.columns.isin(['A', 'C']).any():
    # do something

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^{1: isin() call on the columns returns a boolean array whose values are True if it's either A or C and False otherwise. The truth value of an array is ambiguous, so any() call reduces it to a single True/False value.}