Add column to Pandas DataFrame created by function?

Question

There is a csv file with following urls inside:

1;https://www.one.de 
2;https://www.two.de 
3;https://www.three.de
4;https://www.four.de
5;https://www.five.de

Then I load it to a pandas dataframe df.

cols = ['nr','url']
df = pd.read_csv("listing.csv", sep=';', encoding = "utf8", dtype=str, names=cols)

Then I like to add another col 'domain_name' corresponding to the nr.

def takedn(url):
    m = urlsplit(url)
    return m.netloc.split('.')[-2]

df['domain_name'] = takedn(df['url'].all())
print(df.head())

But it takes the last domain_name for all nr's.

Output:
  nr                   url domain_name
0  1    https://www.one.de        five
1  2    https://www.two.de        five
2  3  https://www.three.de        five
3  4   https://www.four.de        five
4  5   https://www.five.de        five

I try this to learn vectorizing. It will not work as I think. First line the domain_name should be one, second two and so on.

Ynjxsjmh · Accepted Answer · 2021-04-22 14:12:31Z

1

To operate on element, you can use apply().

def takedn(url):
    m = urlsplit(url)
    return m.netloc.split('.')[-2]

df['domain_name'] = df['url'].apply(takedn)

answered Apr 22, 2021 at 14:12

Ynjxsjmh

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4 Comments

orgen Over a year ago

Thanks, perfect answer. Is there a good tutorial or explanation for vectorization? Just for understanding.

Ynjxsjmh Over a year ago

@orgen Not know what do you mean by vectorization. But there is book called Python for Data Analysis teaching you how to use pandas to handle data.

orgen Over a year ago

Found a link here for vectorizing: stackoverflow.com/questions/1422149/what-is-vectorization

Ynjxsjmh Over a year ago

@orgen That seems unrelated with pandas. But if you mainly want to apply functions on pandas. There are mainly three functions apply, map and applymap. For the difference among them, you can refer to stackoverflow.com/questions/19798153.

BENY · Accepted Answer · 2021-04-22 14:23:29Z

1

We have built-in function in tldextract

import tldextract
df['domain'] = df.url.map(lambda x : tldextract.extract(x).domain)
df
   nr                   url domain_name domain
0   1    https://www.one.de        five    one
1   2    https://www.two.de        five    two
2   3  https://www.three.de        five  three
3   4   https://www.four.de        five   four
4   5   https://www.five.de        five   five

answered Apr 22, 2021 at 14:23

BENY

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