Python. List of Lists

Question

I have a list of lists and I should find the sublist whose second element has the max value.

I implemented it as follows, but I would say it's a bit 'suboptimal' :-)

def max_value(inputlist):
    return max([sublist[-1] for sublist in inputlist])

and then

maxvalue = max_value(listofcounties)    
for result in listofcounties:
    if result[1] == maxvalue:
        return result[0]

There's a way to accomplish that in a more coincise form?

Thank you very much for any hint! Bye Fabio

Answer 1

max accepts an optional key parameter; max compares the return value of the key function to determine which one is larger.

maxvalue = max(listofcounties, key=lambda x: x[-1])

---

>>> listofcounties = [['county1', 10], ['county2', 20], ['county3', 5]]
>>> max(listofcounties, key=lambda x: x[-1])  # by using `key`, max compares 10, 20, 5
['county2', 20]

Answer 2

Here is another option (though not a very efficient one):

Find all the sub-lists whose second element has the maximum value:

[n for n in listofcounties if n[1] == max([k[1] for k in listofcounties])]

Find the first sub-list whose second element has the maximum value:

[n for n in listofcounties if n[1] == max([k[1] for k in listofcounties])][0]

---

Split it into two statements in order to improve efficiency:

Find all the sub-lists whose second element has the maximum value:

maxvalue = max([k[1] for k in listofcounties])

[n for n in listofcounties if n[1] == maxvalue]

Find the first sub-list whose second element has the maximum value:

maxvalue = max([k[1] for k in listofcounties])

[n for n in listofcounties if n[1] == maxvalue][0]

Answer 3

Another simple approach using sorted function:

# the exemplary list was borrowed from @falsetru answer
listofcounties = [['county1', 10], ['county2', 20], ['county3', 5]]
max_sequence = sorted(listofcounties, key=lambda l: l[1], reverse=True)[0]

print(max_sequence)

The output:

['county2', 20]

https://docs.python.org/3.5/library/functions.html#sorted