How to check if a column exists in Pandas

Is there a way to check if a column exists in a Pandas DataFrame?

Suppose that I have the following 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']

But first I want to check if df['A'] exists, and if not, I want to calculate df['sum'] = df['B'] + df['C'] instead.

4 Answers

This will work:

if 'A' in df:

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

if 'A' in df.columns:

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']):

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:

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

The DataFrame get method has similar behavior as python dictionaries.

You can use the set's method issuperset:

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