Aggregate with categorical variables but without groupby
#### Code Sample, a copy-pastable example if possible

```python
import pandas as pd 

df = pd.DataFrame( {"col_1" : [1, 2, 3, 4, 5],
                  "col_2" : [3, 5, 3, 4, 9],
                  "col_3" : ["cat", "dog", "dog", "cat", "cat"],
                  "col_4" : ["feline", "canine", "canine", "feline", "feline"]})

func_list = [lambda x : len(x),
             lambda x : x.isnull().sum()]

num_col = df.select_dtypes(include="number").columns
cat_col = df.select_dtypes(include="object").columns

#works correctly for numeric columns
print(df[num_col].agg(func_list))
print(df[cat_col].agg(func_list))

```
#### Problem description

There is an issue with aggregating and applying a list of functions.  These functions should be able to be applied to categorical or object columns but cannot currently. 

#### Expected Output

I would expect the output for the categorical and numeric columns to be the same with these simple functions.

#### Output of ``pd.show_versions()``

INSTALLED VERSIONS
------------------
commit           : None
python           : 3.7.4.final.0
python-bits      : 64
OS               : Darwin
OS-release       : 19.0.0
machine          : x86_64
processor        : i386
byteorder        : little
LC_ALL           : None
LANG             : en_US.UTF-8
LOCALE           : en_US.UTF-8

pandas           : 0.25.1
numpy            : 1.17.2
pytz             : 2019.3
dateutil         : 2.8.0
pip              : 19.2.3
setuptools       : 41.4.0
Cython           : 0.29.13
pytest           : 5.2.1
hypothesis       : None
sphinx           : 2.2.0
blosc            : None
feather          : None
xlsxwriter       : 1.2.1
lxml.etree       : 4.4.1
html5lib         : 1.0.1
pymysql          : None
psycopg2         : None
jinja2           : 2.10.3
IPython          : 7.8.0
pandas_datareader: None
bs4              : 4.8.0
bottleneck       : 1.2.1
fastparquet      : None
gcsfs            : None
lxml.etree       : 4.4.1
matplotlib       : 3.1.1
numexpr          : 2.7.0
odfpy            : None
openpyxl         : 3.0.0
pandas_gbq       : None
pyarrow          : None
pytables         : None
s3fs             : None
scipy            : 1.3.1
sqlalchemy       : 1.3.9
tables           : 3.5.2
xarray           : None
xlrd             : 1.2.0
xlwt             : 1.3.0
xlsxwriter       : 1.2.1

