Extracting columns values based on values in a list

Question

I need to extract values from a column in a dataframe based on the values of another column which I have extracted in a list.

import pandas as pd
data = [[1, 'john', 'kelly'], [2, 'john', 'raj'], [2, 'john', 'leonard'], [3, 'penny', 'stuart'], [3, 'penny', 'halley'], [3, 'penny', 'amy'], [4, 'sheldon', 'will'], [4, 'sheldon', 'richard']]
school = pd.DataFrame(data, columns=['teacher_id', 'teacher_name', 'student_name'])
print(school)

This is my dataframe.

   teacher_id teacher_name student_name
0           1         john        kelly
1           2         john          raj
2           2         john      leonard
3           3        penny       stuart
4           3        penny       halley
5           3        penny          amy
6           4      sheldon         will
7           4      sheldon      richard

From this data frame I have extracted the teacher_id occuring most number of times.

school.teacher_id.value_counts().head()
> 3    3
  2    2
  4    2
  1    1

Now using the above values(teacher_id) how can i get the teacher name?

Answer 1

Instead of using:-

school.teacher_id.value_counts().head()

Use this:-

school[['teacher_id','teacher_name']].value_counts().head()

Or

you can make use of groupby() method:-

school.groupby('teacher_id')['teacher_name'].value_counts().head()