Find maximum value and index in a python list?

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?

Answer 1

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 

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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) 

Answer 2

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]