Pythonic way to get the largest item in a list

Question

Is there a better way of doing this? I don't really need the list to be sorted, just scanning through to get the item with the greatest specified attribute. I care most about readability but sorting a whole list to get one item seems a bit wasteful.

>>> import operator
>>> 
>>> a_list = [('Tom', 23), ('Dick', 45), ('Harry', 33)]
>>> sorted(a_list, key=operator.itemgetter(1), reverse=True)[0]
('Dick', 45)

I could do it quite verbosely...

>>> age = 0
>>> oldest = None
>>> for person in a_list:
...     if person[1] > age:
...             age = person[1]
...             oldest = person
... 
>>> oldest
('Dick', 45)

fengb · Accepted Answer · 2012-07-03 17:35:55Z

54

max(a_list, key=operator.itemgetter(1))

edited Jul 3, 2012 at 17:35

user142162

answered Dec 9, 2009 at 14:21

fengb

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2 Comments

Noah Over a year ago

Nice, didn't know that max had an optional key argument!

Stephen Paulger Over a year ago

Ah, brilliant! Good python makes me happy.

tgray · Accepted Answer · 2009-12-09 14:23:06Z

8

You could use the max function.

Help on built-in function max in module __builtin__:

max(...)

max(iterable[, key=func]) -> value

max(a, b, c, ...[, key=func]) -> value

With a single iterable argument, return its largest item. With two or more arguments, return the largest argument.

max_item = max(a_list, key=operator.itemgetter(1))

answered Dec 9, 2009 at 14:23

tgray

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Comments

Richard Shepherd · Accepted Answer · 2013-11-23 15:20:06Z

The key can also be a lambda, for example:

people = [("Tom", 33), ("Dick", 55), ("Harry", 44)]
oldest = max(people, key=lambda p: p[1])

For some reason, using a lambda makes it feel more like "my code" is doing the work, compared with itemgetter. I think this feels particularly nice when you have a collection of objects:

class Person(object):
    def __init__(self, name, age):
        self.name = name
        self.age = age

people = [Person("Tom", 33), Person("Dick", 55), Person("Harry", 44)]
oldest = max(people, key=lambda p: p.age)

Emil Ivanov · Accepted Answer · 2009-12-09 14:59:20Z

2

Use the max() function or do it FP style:

reduce(lambda max, c: max if c <= max else c, [1, 6, 9, 2, 4, 0, 8, 1, 3])

edited Dec 9, 2009 at 14:59

answered Dec 9, 2009 at 14:23

Emil Ivanov

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Comments

David Shaked · Accepted Answer · 2016-01-27 19:10:20Z

0

Some people mentioned the following solution:

max(nameOfList, key=len)

However, this solution only returns the first sequential element of largest size. So, for example, in the case of list ["ABC","DCE"], only the first item of the list is returned.

To remedy this, I found the following workaround using the filter function:

filter((lambda x: len(x)==len(max(nameOfList, key=len))),nameOfList)

answered Jan 27, 2016 at 19:10

David Shaked

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