How to find the min/max value of a common key in a list of dicts?

I have a list of dictionaries like so:

[{'price': 99, 'barcode': '2342355'}, {'price': 88, 'barcode': '2345566'}]

I want to find the min() and max() prices. Now, I can sort this easily enough using a key with a lambda expression (as found in another Stack Overflow post), so if there is no other way I’m not stuck. However, from what I’ve seen there is almost always a direct way in Python, so this is an opportunity for me to learn a bit more.

Answers:

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Method 1

lst = [{'price': 99, 'barcode': '2342355'}, {'price': 88, 'barcode': '2345566'}]

maxPricedItem = max(lst, key=lambda x:x['price'])
minPricedItem = min(lst, key=lambda x:x['price'])

This tells you not just what the max price is but also which item is most expensive.

Method 2

There are several options. Here is a straight-forward one:

seq = [x['the_key'] for x in dict_list]
min(seq)
max(seq)

[Edit]
If you only wanted to iterate through the list once, you could try this (assuming the values could be represented as ints):

import sys

lo,hi = sys.maxint,-sys.maxint-1
for x in (item['the_key'] for item in dict_list):
    lo,hi = min(x,lo),max(x,hi)

Method 3

I think the most direct (and most Pythonic) expression would be something like:

min_price = min(item['price'] for item in items)

This avoids the overhead of sorting the list — and, by using a generator expression, instead of a list comprehension — actually avoids creating any lists, as well. Efficient, direct, readable… Pythonic!

Method 4

One answer would be mapping your dicts to the value of interest inside a generator expression, and then applying the built-ins min and max.

myMax = max(d['price'] for d in myList)
myMin = min(d['price'] for d in myList)

Method 5

can also use this:

from operator import itemgetter

lst = [{'price': 99, 'barcode': '2342355'}, {'price': 88, 'barcode': '2345566'}]  
max(map(itemgetter('price'), lst))

All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0