Python Question
How can you find the most common sets using python?
I have a pandas dataframe where one column is a list of all courses taken by a student. The index is the student's ID.
I'd like to find the most common set of courses across all students. For instance, if the dataframe looks like this:
ID | Courses
1 [A, C]
2 [A, C]
3 [A, C]
4 [B, C]
5 [B, C]
6 [K, D]
...
Then I'd like the output to return the most common sets and their frequency, something like:
{[A,C]: 3, [B,C]: 2}
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Answer Source
import pandas as pd
# create example data
a = range(6)
b = [['A', 'C'], ['A', 'C'], ['A', 'C'], ['B', 'C'], ['B', 'C'], ['K', 'D']]
df = pd.DataFrame({'ID': a, 'Courses': b})
# convert lists in Courses-column to tuples (which some parts of pandas need)
df['Courses'] = df['Courses'].apply(lambda x: tuple(x))
print(df.Courses.value_counts())
Output:
(A, C) 3
(B, C) 2
(K, D) 1
Name: Courses, dtype: int64
Edit (as my answer was accepted):
jezrael describes (first as a comment to my answer) a much more compact version of the same approach:
a = range(6)
b = [['A', 'C'], ['A', 'C'], ['A', 'C'], ['B', 'C'], ['B', 'C'], ['K', 'D']]
df = pd.DataFrame({'ID': a, 'Courses': b})
print(df.Courses.value_counts()) # list->tuple and counting in one line!
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