Python's most efficient way to choose longest string in list?

Question

I have a list of variable length and am trying to find a way to test if the list item currently being evaluated is the longest string contained in the list. And I am using Python 2.6.1

For example:

mylist = ['abc','abcdef','abcd']

for each in mylist:
    if condition1:
        do_something()
    elif ___________________: #else if each is the longest string contained in mylist:
        do_something_else()

Surely there's a simple list comprehension that's short and elegant that I'm overlooking?

Paolo Bergantino · Accepted Answer · 2009-05-16 21:19:46Z

781

From the Python documentation itself, you can use max:

>>> mylist = ['123','123456','1234']
>>> print max(mylist, key=len)
123456

answered May 16, 2009 at 21:19

Paolo Bergantino

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8 Comments

Kumba Over a year ago

Won't work for Python 2.4. See this post and this post for code to implement under 2.4.

Anderson Green Over a year ago

It only returns the first longest string: for example, print(max(["this", "does", "work"], key=len)) only returns "this" instead of returning all of the longest strings.

David Shaked Over a year ago

ditto @AndersonGreen. Can the method be redeployed in a way that captures two+ elements of the list meeting the call (key) equally well?

David Shaked Over a year ago

Following up on my question from earlier, I've linked a response that remedies the first-item-if-all-else-equal problem...

Thomas Ahle Over a year ago

To get every largest element, in linear time, you have to do m=max(map(len,xs)); [x for x in xs if len(x) == m]. I don't think it can be done nicely in one line.

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pableiros · Accepted Answer · 2016-12-15 00:16:38Z

16

def longestWord(some_list): 
    count = 0    #You set the count to 0
    for i in some_list: # Go through the whole list
        if len(i) > count: #Checking for the longest word(string)
            count = len(i)
            word = i
    return ("the longest string is " + word)

or much easier:

max(some_list , key = len)

edited Dec 15, 2016 at 0:16

pableiros

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answered Dec 14, 2016 at 23:26

Savo Vukovic

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1 Comment

Wayne Workman Over a year ago

The logestWord definition here should be the accepted answer because it handles strings with spaces. The max() function does not handle this.

Elazar Leibovich · Accepted Answer · 2009-05-16 21:22:37Z

9

What should happen if there are more than 1 longest string (think '12', and '01')?

Try that to get the longest element

max_length,longest_element = max([(len(x),x) for x in ('a','b','aa')])

And then regular foreach

for st in mylist:
    if len(st)==max_length:...

answered May 16, 2009 at 21:22

Elazar Leibovich

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Comments

Sergey Bushmanov · Accepted Answer · 2020-12-11 17:55:56Z

4

To get the smallest or largest item in a list, use the built-in min and max functions:

 lo = min(L)
 hi = max(L)

As with sort, you can pass in a "key" argument that is used to map the list items before they are compared:

 lo = min(L, key=int)
 hi = max(L, key=int)

http://effbot.org/zone/python-list.htm

Looks like you could use the max function if you map it correctly for strings and use that as the comparison. I would recommend just finding the max once though of course, not for each element in the list.

edited Dec 11, 2020 at 17:55

Sergey Bushmanov

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answered May 16, 2009 at 21:20

Gavin H

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1 Comment

daddyodevil Over a year ago

1) doesn't work for string with spaces, 2) throws err using list of strings from my example: ValueError: invalid literal for int() with base 10: 'dd'

HarryM · Accepted Answer · 2009-05-16 21:20:36Z

3

len(each) == max(len(x) for x in myList) or just each == max(myList, key=len)

answered May 16, 2009 at 21:20

HarryM

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1 Comment

David Shaked Over a year ago

can you provide a brief explanation?

daddyodevil · Accepted Answer · 2023-07-03 05:28:16Z

1

This is a linear time implementation I came up with. If there exists multiple elements of the same size, then will return the first element with the largest size. :

s = ["a", "b", "c", "d", "aa", "bb", "cc", "dd", "ddd", "dd d"]
maxl = ""
for i in s:
    if len(i) > len(maxl):
        maxl = i
print(maxl)

If you want the index of the string with max length you can use the following:

s = ["a", "b", "c", "d", "aa", "bb", "cc", "dd", "ddd", "dd d"]
shuffle(s)   #from random import shuffle
print(s)
maxl_idx = 0
for i,j in enumerate(s):
    if len(j) > len(s[maxl_idx]):
        maxl_idx = i
print(maxl_idx, '\t', s[maxl_idx])

edited Jul 3, 2023 at 5:28

answered Jun 28, 2023 at 7:39

daddyodevil

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Comments

Stijn Van den Bruel · Accepted Answer · 2011-10-21 23:21:47Z

0

def LongestEntry(lstName):
  totalEntries = len(lstName)
  currentEntry = 0
  longestLength = 0
  while currentEntry < totalEntries:
    thisEntry = len(str(lstName[currentEntry]))
    if int(thisEntry) > int(longestLength):
      longestLength = thisEntry
      longestEntry = currentEntry
    currentEntry += 1
  return longestLength

answered Oct 21, 2011 at 23:21

Stijn Van den Bruel

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