How do I keep only min and max values of sublists within a list?

Question

I have a dataframe column as:

df = pd.DataFrame({'a':[1,3,5,7,4,5,6,4,7,8,9]})

My output list needed is (keeping the min max values of ranges):

[[1,4],[5,7],[8,9]]

Here's how far I got:

import pandas as pd
df = pd.DataFrame({'a':[1,3,5,7,4,5,6,4,7,8,9]})

# Convert df column to a unique value list and sort ascending
us = df['a'].unique().tolist()
us.sort()
lst1 = [int(v) for v in us]

# Create 3 groups of values
lst2 = [lst1[i:i + 3] for i in xrange(0, len(lst1), 3)]

# Keep only min and max of these groups

How do I convert this:

[[1,3,4],[5,6,7],[8,9]]  

to my desired output?

Answer 1

You can use a list comprehension for this:

lst3 = [[min(i), max(i)] for i in lst2]

Answer 2

You can use dataframe

df = df.sort_values("a").drop_duplicates().reset_index(drop=True)
df.groupby(df.index // 3).agg(['min', 'max']).values.tolist()