human
join column entried.
assistant
Here is a Python code to join columns entered into a column

import pandas as pd

def join_column_entries(column_entries):
    """
    Given a list of column entries, will return a list of
    column entries with the same order as the input list,
    but with the duplicate entries removed.
    """
    dedup = set()
    return [ x for x in column_entries if not (x in dedup or dedup.add(x))]

# Enter the data
column_entries = ['a', 'a', 'b', 'b', 'c', 'c', 'd', 'd', 'e', 'e', 'f', 'f']

# Calling the function
print((join_column_entries(column_entries)))

#Example Output
# ['a', 'b', 'c', 'd', 'e', 'f']

#Remember to inspect code for bugs.