Slice series based on values in another series of the same data frame

Question

I have a data frame sample below and trying to get to the following output. Have looked through a lot of examples but none seem to handle this specific scenario. See the sample data.

Not sure if there is a way to achieve this using apply or map but I am not tied to it.


df = pd.DataFrame({'collen': [5, 3, 2, None, 3], 'colstr': ['turquoise', 'white', 'blue', 'red',None]})

    collen  colstr
0   5.0     turquoise
1   3.0     white
2   2.0     blue
3   NaN     red
4   3.0     None

Expected outcome:

    collen  colstr      new_col_str
0   5.0     turquoise   turqu
1   3.0     white       whi
2   2.0     blue        bl
3   NaN     red         red
4   3.0     None        None

Haleemur Ali · Accepted Answer · 2020-11-06 03:44:44Z

1

if you're on a recent version of pandas supporting nullale integers (Int64), then first cast collen to Int64. Then use that as for string slicing.

df.collen = df.collen.astype('Int64')

next, use the following lambda to generate the new column

df['new_col_str'] = df.apply(
    lambda x: x.colstr if pd.isnull(x.colstr) or pd.isnull(x.collen) else x.colstr[:x.collen], 
    axis=1
    )

answered Nov 6, 2020 at 3:44

Haleemur Ali

28.6k6 gold badges67 silver badges89 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Drj Over a year ago

on the same note, is there a way to do a contain search across series? i.e the output is a boolean flag if the string of col1 in given row is contained within the string of col2 of the same row.

Haleemur Ali Over a year ago

@Drj, not sure what you mean, please make a full post with example input output & attempt to help SO community answer your question

BENY · Accepted Answer · 2020-11-06 03:45:20Z

1

Try with two condition here :-)

df['new'] = df.apply(lambda x : x['colstr'] if pd.isnull(x['collen']) or pd.isnull(x['colstr']) else x['colstr'][:int(x['collen'])],axis=1)
df
Out[98]: 
   collen     colstr    new
0     5.0  turquoise  turqu
1     3.0      white    whi
2     2.0       blue     bl
3     NaN        red    red
4     3.0       None   None

answered Nov 6, 2020 at 3:45

BENY

324k22 gold badges176 silver badges250 bronze badges

Comments

Bill Huang · Accepted Answer · 2020-11-06 03:44:52Z

0

def f(row):
    if row["colstr"] is None:
        return None
    elif pd.isna(row["collen"]):
        return row["colstr"]
    else:
        return row["colstr"][:int(row["collen"])]

df.apply(f, axis=1)

Result

0    turqu
1      whi
2       bl
3      red
4     None
dtype: object

answered Nov 6, 2020 at 3:44

Bill Huang

4,6772 gold badges15 silver badges37 bronze badges

Collectives™ on Stack Overflow

Slice series based on values in another series of the same data frame

3 Answers 3

2 Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

2 Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related