I have a pandas dataframe with year in one column, and a text field in another.

I have a series of keywords.

I wish to return the amount of rows containing each keyword grouped by year.

How can I do this?

e.g.

```py
import pandas as pd

txt = """2019  'an example sentence'
2019  'another sentence'
2020  'fox trot'
2020  'this sentence has some new words'
2020  'new and old example words here'
2021  'the fox jumps for example'
2021  'a different example sentence'"""

df = pd.DataFrame([x.split('  ') for x in txt.split('\n')], columns=['year','text'])

```

```
keywords = ['example', 'sentence', 'fox']

```

Output:

```
year  example  sentence  fox 
2019  1        2         0
2020  0        1         1
2021  2        0         1

```