Calculating with Dictionaries

Problem

You want to perform various calculations on a dictionary of data.

Solution

In order to perform useful calculations on the dictionary contents, it is often useful to invert the keys and values of the dictionary using zip().



In [1]:

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



In [4]:

    
# Find the minimum and maximum price and stock name
min_price = min(zip(prices.values(), prices.keys())) # min_price is (10.75, 'FB')
max_price = max(zip(prices.values(), prices.keys())) # max_price is (612.78, 'AAPL')

print(min_price)
print(max_price)









    



(10.75, 'FB')
(612.78, 'AAPL')



In [5]:

    
# Ranking
prices_sorted = sorted(zip(prices.values(), prices.keys())) 
# prices_sorted is [(10.75, 'FB'), (37.2, 'HPQ'),
#                   (45.23, 'ACME'), (205.55, 'IBM'),
#                   (612.78, 'AAPL')]
print(prices_sorted)









    



[(10.75, 'FB'), (37.2, 'HPQ'), (45.23, 'ACME'), (205.55, 'IBM'), (612.78, 'AAPL')]

Be aware that zip() creates an iterator that can only be consumed once.



In [7]:

    
prices_and_names = zip(prices.values(), prices.keys()) 
print(min(prices_and_names)) # OK
print(max(prices_and_names)) # ValueError: max() arg is an empty sequence









    



(10.75, 'FB')






    



---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-7-79e371c3f80e> in <module>()
      1 prices_and_names = zip(prices.values(), prices.keys())
      2 print(min(prices_and_names)) # OK
----> 3 print(max(prices_and_names)) # ValueError: max() arg is an empty sequence

ValueError: max() arg is an empty sequence