Pythonic way to find maximum value and its index in a list

Question

If I want the maximum value in a list  I can just write max List   but what if I also need the index of the maximum value   I can write something like this   maximum 0 for i value in enumerate List       if value gt maximum          maximum value         index i   But it looks tedious to me   And if I write   List index max List     Then it will iterate the list twice   Is there a better way

User · Answer

With Python s built-in library  it s pretty easy   a    2  9  -10  5  18  9   max xrange len a    key   lambda x  a x     This tells max to find the largest number in the list  0  1  2       len a    using the custom function lambda x  a x   which says that 0 is actually 2  1 is actually 9  etc

User · Answer

I think the accepted answer is great  but why don t you do it explicitly  I feel more people would understand your code  and that is in agreement with PEP 8   max value   max my list  max index   my list index max value    This method is also about three times faster than the accepted answer   import random from datetime import datetime import operator  def explicit l       max val   max l      max idx   l index max val      return max idx  max val  def implicit l       max idx  max val   max enumerate l   key operator itemgetter 1       return max idx  max val  if   name         main         from timeit import Timer     t   Timer  explicit l     from   main   import explicit  implicit               import random  import operator              l    random random   for   in xrange 100         print  Explicit    2f usec pass     1000000   t timeit number 100000  100000       t   Timer  implicit l     from   main   import explicit  implicit               import random  import operator              l    random random   for   in xrange 100         print  Implicit    2f usec pass     1000000   t timeit number 100000  100000    Results as they run in my computer   Explicit  8 07 usec pass Implicit  22 86 usec pass   Other set   Explicit  6 80 usec pass Implicit  19 01 usec pass

User · Answer

max   v i  for i v in enumerate my list

User · Answer

sorry for reviving this thread  but thought my method was worth adding   The list name in this example  list   list sort   print list -1     That will print the highest value in the list easy as   list sort   sorts the list by the value of the item in the ASCII table  so effectively sorts the list lowest to highest  I then just print the last value in the list  which will be the greatest number  by using print list -1     Hope this helps

User · Answer

I would suggest a very simple way   import numpy as np l    10  22  8  8  11  print np argmax l   print np argmin l     Hope it helps

User · Answer

Here is a complete solution to your question using Python s built-in functions     Create the List numbers   input  Enter the elements of the list  Separate each value with a comma  Do not put a comma at the end  n   split          Convert the elements in the list  treated as strings  to integers numberL    int element  for element in numbers      Loop through the list with a for-loop  for elements in numberL      maxEle   max numberL      indexMax   numberL index maxEle   print maxEle  print indexMax

User · Answer

max   value index  for index value in enumerate your list     if maximum value is present more than once in your list then this will return index of the last occurrence   If maximum value in present more than once and you want to get all indices   max value   max your list  maxIndexList    index for index value in enumerate your list  if value  max your list

User · Answer

I made some big lists  One is a list and one is a numpy array  import numpy as np import random arrayv np random randint 0 10  100000000 1   listv    for i in range 0 100000000       listv append random randint 0 9    Using jupyter notebook s   time function I can compare the speed of various things  2 seconds    time listv index max listv    54 6 seconds    time listv index max arrayv    6 71 seconds    time np argmax listv   103 ms    time np argmax arrayv   numpy s arrays are crazy fast

User · Answer

There are many options  for example   import operator index  value   max enumerate my list   key operator itemgetter 1

User · Answer

This answer is 33 times faster than  Escualo assuming that the list is very large  and assuming that it s already an np array     I had to turn down the number of test runs because the test is looking at 10000000 elements not just 100   import random from datetime import datetime import operator import numpy as np  def explicit l       max val   max l      max idx   l index max val      return max idx  max val  def implicit l       max idx  max val   max enumerate l   key operator itemgetter 1       return max idx  max val  def npmax l       max idx   np argmax l      max val   l max idx      return  max idx  max val   if   name         main         from timeit import Timer  t   Timer  npmax l     from   main   import explicit  implicit  npmax           import random  import operator  import numpy as np          l   np array  random random   for   in xrange 10000000      print  Npmax    2f msec pass     1000    t timeit number 10  10    t   Timer  explicit l     from   main   import explicit  implicit           import random  import operator          l    random random   for   in xrange 10000000     print  Explicit    2f msec pass     1000    t timeit number 10  10    t   Timer  implicit l     from   main   import explicit  implicit           import random  import operator          l    random random   for   in xrange 10000000     print  Implicit    2f msec pass     1000    t timeit number 10  10     Results on my computer   Npmax  8 78 msec pass Explicit  290 01 msec pass Implicit  790 27 msec pass

User · Answer

Maybe you need a sorted list anyway   Try this    your list    13  352  2553  0 5  89  0 4  sorted list   sorted your list  index of higher value   your list index sorted list -1

[python] Pythonic way to find maximum value and its index in a list?

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