Extracting a Subset of a Dictionary

Problem

This is easily accomplished using a dictionary comprehension.

Solution

The easiest way to filter sequence data is often to use a list comprehension.



In [1]:

    
from pprint import pprint

prices = {
   'ACME': 45.23,
   'AAPL': 612.78,
   'IBM': 205.55,
   'HPQ': 37.20,
   'FB': 10.75
}

# Make a dictionary of all prices over 200
p1 = { key:value for key, value in prices.items() if value > 200 }

print("All prices over 200")
pprint(p1)









    



All prices over 200
{'AAPL': 612.78, 'IBM': 205.55}



In [2]:

    
# Make a dictionary of tech stocks
tech_names = { 'AAPL', 'IBM', 'HPQ', 'MSFT' }
p2 = { key:value for key,value in prices.items() if key in tech_names }

print("All techs")
pprint(p2)









    



All techs
{'AAPL': 612.78, 'HPQ': 37.2, 'IBM': 205.55}

Discussion

You can also use tuple() or another rewrite of dict comprehension



In [3]:

    
p1 = dict((key, value) for key, value in prices.items() if value > 200)
print(p1)









    



{'IBM': 205.55, 'AAPL': 612.78}



In [4]:

    
# Make a dictionary of tech stocks
tech_names = { 'AAPL', 'IBM', 'HPQ', 'MSFT' }
p2 = { key:prices[key] for key in prices.keys() & tech_names }
print(p2)









    



{'IBM': 205.55, 'HPQ': 37.2, 'AAPL': 612.78}