Human: filter based on list index. Assistant: 
Here is a Python code for a filter based on list index

import pandas as pd

def filter_by_index(l, index):
    """
    Filter a list based on list index
    """
    return [item for item in l if item[0] == index]

# Enter the list
l = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]

# Enter the index
index = 1

# Calling the function
print((filter_by_index(l, index)))

#Example Output
# [[1, 2, 3]]

#Remember to inspect code for bugs.