Find maximum value and index in a python list? [duplicate]

Question

I have a python list that is like this,

[[12587961, 0.7777777777777778], [12587970, 0.5172413793103449], [12587979, 0.3968253968253968], [12587982, 0.88], [12587984, 0.8484848484848485], [12587992, 0.7777777777777778], [12587995, 0.8070175438596491], [12588015, 0.4358974358974359], [12588023, 0.8985507246376812], [12588037, 0.5555555555555555], [12588042, 0.9473684210526315]]

This list can be up to thousand elements in length, how can I get the maximum value in the list according to the second item in the sub-array, and get the index of the maximum value which is the fist element in the sub-array in python?

You are right @unwind. I think he wants to find all the elements with maximum value according to the second element and find the maximum out of them based on the first value. — thefourtheye
– thefourtheye, Commented Sep 28, 2016 at 13:43
well sorry if you guys didn't get it, it's like this I want the subarray with the maximum second value, second value means the [1]th item in a subarray — rksh
– rksh, Commented Sep 28, 2016 at 13:51
Okay ... I still struggle to understand. A small example on e.g. a four or five element list would be helpful. But I guess it's already solved. — unwind
– unwind, Commented Sep 28, 2016 at 13:52
@rksh What if more than one subarray has got the maximum second value? — thefourtheye
– thefourtheye, Commented Sep 28, 2016 at 13:54

thefourtheye · Accepted Answer · 2016-09-28 13:47:10Z

Use the max function and its key parameter, to use only the second element to compare elements of the list.

For example,

>>> data = [[12587961, 0.7777777777777778], [12587970, 0.5172413793103449], [12587979, 0.3968253968253968].... [12588042, 0.9473684210
526315]]
>>> max(data, key=lambda item: item[1])
[12588042, 0.9473684210526315]

Now, if you want just the first element, then you can simply get the first element alone, or just unpack the result, like this

>>> index, value = max(data, key=lambda item: item[1])
>>> index
12588042
>>> value
0.9473684210526315

Edit: If you want to find the maximum index (first value) out of all elements with the maximum value (second value), then you can do it like this

>>> _, max_value = max(data, key=lambda item: item[1])
>>> max(index for index, value in data if value == max_value)

You can do the same in a single iteration, like this

max_index = float("-inf")
max_value = float("-inf")

for index, value in data:
      if value > max_value:
          max_value = value
          max_index = index
      elif value == max_value:
          max_index = max(max_index, index)

Thanks actually what I wanted was the something like you mentioned in the original answer, the subarray with the maxumum second value in a subarray :) is there a way to get the n number of arrays with the maximum value, like top 10 highest values :)
@rksh You should give proper examples. The words are simply confusing.
ok i will take a simple example if there is an array like this data = [1,2,5,7,6,8,3,9,4] how can i get the three maximum values? in this case it's 7,8,9

Patrick Haugh · Accepted Answer · 2016-09-28 13:30:28Z

5

Use max with a key.

l = [[12587961, 0.7777777777777778], [12587970, 0.5172413793103449], [12587979, 0.3968253968253968], [12587982, 0.88], [12587984, 0.8484848484848485], [12587992, 0.7777777777777778], [12587995, 0.8070175438596491], [12588015, 0.4358974358974359], [12588023, 0.8985507246376812], [12588037, 0.5555555555555555], [12588042, 0.9473684210526315]]
max_sub = max(l, key=lambda x: x[1])
max_val = max_sub[1]
max_index = max_sub[0]

answered Sep 28, 2016 at 13:30

Patrick Haugh

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Alicia Garcia-Raboso · Accepted Answer · 2016-09-28 13:29:35Z

1

from operator import itemgetter

a = [[12587961, 0.7777777777777778], [12587970, 0.5172413793103449], [12587979, 0.3968253968253968], [12587982, 0.88], [12587984, 0.8484848484848485], [12587992, 0.7777777777777778], [12587995, 0.8070175438596491], [12588015, 0.4358974358974359], [12588023, 0.8985507246376812], [12588037, 0.5555555555555555], [12588042, 0.9473684210526315]]

max(a, key=itemgetter(1))[0]
// => 12588042

answered Sep 28, 2016 at 13:29

Alicia Garcia-Raboso

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Janarthanan .S · Accepted Answer · 2016-09-28 13:58:52Z

allData = [[12587961, 0.7777777777777778], [12587970, 0.5172413793103449], [12587979, 0.3968253968253968], [12587982, 0.88], [12587984, 0.8484848484848485], [12587992, 0.7777777777777778], [12587995, 0.8070175438596491], [12588015, 0.4358974358974359], [12588023, 0.8985507246376812], [12588037, 0.5555555555555555], [12588042, 0.9473684210526315]]

listOfSecondData = [i[1] for i in allData]
result = allData[listOfSecondData.index(max(listOfSecondData))][0]

print(result)
#Output: 12588042

TanJay · Accepted Answer · 2016-10-01 03:27:27Z

Simple

list = [[12587961, 0.7777777777777778], [12587970, 0.5172413793103449], [12587979, 0.3968253968253968], [12587982, 0.88], [12587984, 0.8484848484848485], [12587992, 0.7777777777777778], [12587995, 0.8070175438596491], [12588015, 0.4358974358974359], [12588023, 0.8985507246376812], [12588037, 0.5555555555555555], [12588042, 0.9473684210526315]]
list2 = []

for x in list:
    list2.append(x[1])
print "index->" + str(list[list2.index(max(list2))][0])
print "max value->" + str(list[list2.index(max(list2))][1])

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