在嵌套列表的第二列中查找最大值？

Question

I have a list like this:

alkaline_earth_values = [['beryllium',  4], 
                         ['magnesium', 12],
                         ['calcium',   20],
                         ['strontium', 38], 
                         ['barium',    56], 
                         ['radium',    88]]

If I simply use the max(list) method, it will return the answer 'strontium' , which would be correct if I was trying to find the max name , however I'm trying to return the element whose integer is highest.

Answer 1

max(alkaline_earth_values, key=lambda x: x[1])

The reason this works is because the key argument of the max function specifies a function that is called when max wants to know the value by which the maximum element will be searched. max will call that function for each element in the sequence. And lambda x: x[1] creates a small function which takes in a list and returns the first (counting starts from zero) element. So

k = lambda x: x[1]

is the same as saying

def k(l):
  return l[1]

but shorter and nice to use in situations like this.

Answer 2

使用key参数。

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

Answer 3

it is rather tricky to assume that an item in a list is actually still a number. If the numbers have become strings, the max() will return the 'value' with the highest first number:

alkaline_earth_values = [['beryllium', '9'], ['magnesium', '12'],['calcium', '20'],
                         ['strontium', '38'], ['barium', '56'], ['radium', '88']]
max(alkaline_earth_values, key=lambda x: x[1])

returns ['beryllium', '9']

max(alkaline_earth_values, key=lambda x: float(x[1]))

will do the trick, when you are sure it will be a number

Answer 4

For high speed consider pandas or numpy:

Import pandas as pd
alkaline_earth_values = [['beryllium', 4], ['magnesium', 12],['calcium', 20],
                     ['strontium', 38], ['barium', 56], ['radium', 88]]
pd.DataFrame(alkaline_earth_values)[1].max()

Answer 5

You could convert your list of lists to a Counter and the call the .most_common() method. This easily allow you to find the maximum or top n values:

>>> from collections import Counter
>>> Counter(dict(alkaline_earth_values)).most_common(1)
[('radium', 88)]
>>> Counter(dict(alkaline_earth_values)).most_common(3)
[('radium', 88), ('barium', 56), ('strontium', 38)]