return default if pandas dataframe.loc location doesn't exist

Question

I find myself often having to check whether a column or row exists in a dataframe before trying to reference it. For example I end up adding a lot of code like:

Answer 1

There is a method for Series:

So you could do:

df.mycol.get(myIndex, NaN)

Example:

In [117]:

df = pd.DataFrame({'mycol':arange(5), 'dummy':arange(5)})
df
Out[117]:
   dummy  mycol
0      0      0
1      1      1
2      2      2
3      3      3
4      4      4

[5 rows x 2 columns]
In [118]:

print(df.mycol.get(2, NaN))
print(df.mycol.get(5, NaN))
2
nan

Answer 2

Python has this mentality to ask for forgiveness instead of permission. You'll find a lot of posts on this matter, such as this one.

In Python catching exceptions is relatively inexpensive, so you're encouraged to use it. This is called the EAFP approach.

For example:

try:
    x = df.loc['myindex', 'mycol']
except KeyError:
    x = mydefault