string split with expand=True. Can anyone explain what is the meaning?

Question

all_data['Title']= all_data['Name'].str.split(', ', expand=True)[1].str.split('.', expand=True)[0]

Can anyone explain what is the meaning of this line of code? Especially with the expand=True and [1] [0].

Answer 1

Take a look here: pandas.Series.str.split

Expand the split strings into separate columns.

If True, return DataFrame/MultiIndex expanding dimensionality.

If False, return Series/Index, containing lists of strings.

s = pd.Series(
    [
        "this is a regular sentence",
    ]
)    
s.str.split(expand=True)

0 1 2 3 4
this is a regular sentence

Answer 2

If you are using Pandas it is likely that you know also Jupyter Notebooks. So, for simplicity and readability let's complete the code you've posted with some additional information in a Notebook-like format:

(this markdown is here to override an error in the answer window interpreter)

```lang-python
    import pandas as pd
    
    raw_name = ['Bob, Mr. Ross', 'Alice, Mrs. Algae', 'Larry, Mr. lemon', 'John, Mr. Johnson']
    all_data = pd.DataFrame({'Name': raw_name})
    
    # This the OP's line
    all_data['Title'] = all_data['Name'].str.split(', ', expand=True)[1].str.split('.', expand=True)[0]
    
    all_data

	Name	Title
0	Bob, Mr. Ross	Mr
1	Alice, Mrs. Algae	Mrs
2	Larry, Mr. Lemon	Mr
3	John, Mr. Johnson	Mr

Where the expand=True renders a set of columns of strings. Therefore, after the first split, you may apply again another str.split method since the first split has rendered dataframe of strings as columns. This would have been a little more complicated with a regular split (or expand=False) which renders a series of lists.

Better explained with code examples:

    all_data['Name'].str.split(', ', expand=False) # or no expand at all

	0
0	[Bob, Mr. Ross]
1	[Alice, Mrs. Algae]
2	[Larry, Mr. Lemon]
3	[John, Mr. Johnson]

    all_data['Name'].str.split(', ', expand=True) 

	0	1
0	Bob	Mr. Ross
1	Alice	Mrs. Algae
2	Larry	Mr. Lemon
3	John	Mr. Johnson

    all_data['Name'].str.split(', ', expand=True)[1].str.split('.', expand=False)

	0
0	[Mr, Ross]
1	[Mrs, Algae]
2	[Mr, Lemon]
3	[Mr, Johnson]

    all_data['Name'].str.split(', ', expand=True)[1].str.split('.', expand=True)

	0	1
0	Mr	Ross
1	Mrs	Algae
2	Mr	Lemon
3	Mr	Johnson

Reference: https://pandas.pydata.org/pandas-docs/stable/reference/api/pandas.Series.str.split.html