OneHotEncoder only a single feature which is string

Question

I want one of my ONLY ONE of my features to be converted to a separate binary features:

df["pattern_id"]
Out[202]: 
0       3
1       3
...
7440    2
7441    2
7442    3
Name: pattern_id, Length: 7443, dtype: int64 
df["pattern_id"]
Out[202]: 
0       0 0 1
1       0 0 1
...
7440    0 1 0
7441    0 1 0
7442    0 0 1
Name: pattern_id, Length: 7443, dtype: int64 

I want to use OneHotEncoder, data is int, so no need to encode it:

onehotencoder = OneHotEncoder(categorical_features=["pattern_id"])
df = onehotencoder.fit_transform(df).toarray()

ValueError: could not convert string to float: 'http://www.zaragoza.es/sedeelectronica/'

Interesting enough I receive an error... sklearn tried to encode another column, not the one I wanted.

We have to encode pattern_id to be an integer value

I used this link: Issue with OneHotEncoder for categorical features

#transform the pattern_id feature to int
encoding_feature = ["pattern_id"]
enc = LabelEncoder()
enc.fit(encoding_feature)
working_feature = enc.transform(encoding_feature)
working_feature = working_feature.reshape(-1, 1)
ohe = OneHotEncoder(sparse=False)


#convert the pattern_id feature to separate binary features
onehotencoder = OneHotEncoder(categorical_features=working_feature, sparse=False)
df = onehotencoder.fit_transform(df).toarray()

And I get the same error. What am I doing wrong ?

Edit

source: https://github.com/martin-varbanov96/scraper/blob/master/logo_scrape/logo_scrape/analysis.py

df
Out[259]: 
      found_img  is_http                                           link_img  \
0          True        0                                  img/aahoteles.svg   
//www.zaragoza.es/cont/paginas/img/sede/logo_e...   

      pattern_id                                       current_link  site_id  \
0              3             https://www.aa-hoteles.com/es/reservas        3   
6              3      https://www.aa-hoteles.com/es/ofertas-hoteles        3   
7              2           http://about.pressreader.com/contact-us/        4   
8              3           http://about.pressreader.com/contact-us/        4   

      status                                   link_id  
0        200               https://www.aa-hoteles.com/  
1        200               https://www.365travel.asia/  
2        200               https://www.365travel.asia/  
3        200               https://www.365travel.asia/  
4        200               https://www.aa-hoteles.com/  
5        200               https://www.aa-hoteles.com/  
6        200               https://www.aa-hoteles.com/  
7        200              http://about.pressreader.com  
8        200              http://about.pressreader.com  
9        200               https://www.365travel.asia/  
10       200               https://www.365travel.asia/  
11       200               https://www.365travel.asia/  
12       200               https://www.365travel.asia/  
13       200               https://www.365travel.asia/  
14       200               https://www.365travel.asia/  
15       200               https://www.365travel.asia/  
16       200               https://www.365travel.asia/  
17       200               https://www.365travel.asia/  
18       200              http://about.pressreade 

[7443 rows x 8 columns]

Answer 1

If you take a look at the documentation for OneHotEncoder you can see that the categorical_features argument expects '“all” or array of indices or mask' not a string. You can make your code work by changing to the following lines

import pandas as pd
from sklearn.preprocessing import OneHotEncoder
# Create a dataframe of random ints
df = pd.DataFrame(np.random.randint(0, 4, size=(100, 4)),
                  columns=['pattern_id', 'B', 'C', 'D'])
onehotencoder = OneHotEncoder(categorical_features=[df.columns.tolist().index('pattern_id')])
df = onehotencoder.fit_transform(df)

However df will no longer be a DataFrame, I would suggest working directly with the numpy arrays.

Answer 2

You can also do it like this

import pandas as pd
from sklearn.preprocessing import OneHotEncoder
onehotenc = OneHotEncoder()
X = onehotenc.fit_transform(df.required_column.values.reshape(-1, 1)).toarray()

We need to reshape the column, because fit_transform requires a 2-D array. Then you can add columns to this numpy array and then merge it with your DataFrame.

Seen from this link here