I have a pandas dataframe with various columns, one of which is a string that I split into a list, using the split command:

```
    import Pandas as pd

    csvRead = pd.read_csv('../data/Data.csv')
    df = pd.DataFrame(csvRead)

    df['split_string'] = df['string'].str.split(r'[ ]')

    idx = 0
    for i in df['split_string']:
        df['split_string_counts'][idf] = len(i)
        i += 1

```

Now I want to vectorize the for statement, because there is no standard command in the Pandas.Series pacakge that can count the number of elements for the list given by the split command. The dataframe df has more than 2 million entries, so the for is very inefficient.