Check if dataframe column is Categorical

Question

I can\'t seem to get a simple dtype check working with Pandas\' improved Categoricals in v0.15+. Basically I just want something like is_categorical(column) -> True

Answer 1

First, the string representation of the dtype is 'category' and not 'categorical', so this works:

In [41]: df.cat_column.dtype == 'category'
Out[41]: True

But indeed, as you noticed, this comparison gives a TypeError for other dtypes, so you would have to wrap it with a try .. except .. block.

---

Other ways to check using pandas internals:

In [42]: isinstance(df.cat_column.dtype, pd.api.types.CategoricalDtype)
Out[42]: True

In [43]: pd.api.types.is_categorical_dtype(df.cat_column)
Out[43]: True

For non-categorical columns, those statements will return False instead of raising an error. For example:

In [44]: pd.api.types.is_categorical_dtype(df.x)
Out[44]: False

For much older version of pandas, replace pd.api.types in the above snippet with pd.core.common.