Python – Limit the values to keys in a Dictionary List

When working with a list of dictionaries, you often need to find the minimum and maximum values for each key across all dictionaries. Python provides the min() and max() functions to efficiently limit values to their bounds.

Example

Below is a demonstration of finding min/max values for each key ?

my_list = [{"python": 4, "is": 7, "best": 10},
           {"python": 2, "is": 5, "best": 9},
           {"python": 1, "is": 2, "best": 6}]

print("The list is :")
print(my_list)

my_result = dict()

keys = list(my_list[0].keys())

for my_elem in keys:
    my_result[my_elem] = [min(sub[my_elem] for sub in my_list), max(sub[my_elem] for sub in my_list)]

print("The result is :")
print(my_result)

Output

The list is :
[{'python': 4, 'is': 7, 'best': 10}, {'python': 2, 'is': 5, 'best': 9}, {'python': 1, 'is': 2, 'best': 6}]
The result is :
{'python': [1, 4], 'is': [2, 7], 'best': [6, 10]}

How It Works

• A list of dictionaries is defined with three dictionaries containing the same keys

• An empty dictionary my_result is created to store the results

• The keys from the first dictionary are extracted using keys() method

• For each key, we use generator expressions with min() and max() to find bounds

• The result stores each key mapped to a list containing [minimum_value, maximum_value]

Alternative Approach Using Dictionary Comprehension

You can achieve the same result more concisely using dictionary comprehension ?

my_list = [{"python": 4, "is": 7, "best": 10},
           {"python": 2, "is": 5, "best": 9},
           {"python": 1, "is": 2, "best": 6}]

result = {key: [min(d[key] for d in my_list), max(d[key] for d in my_list)] 
          for key in my_list[0].keys()}

print("The result is :")
print(result)

The result is :
{'python': [1, 4], 'is': [2, 7], 'best': [6, 10]}

Conclusion

Use min() and max() with generator expressions to efficiently find value bounds across dictionary lists. Dictionary comprehension provides a more concise alternative for the same operation.