Question

Suppose I have a nested list as the one below:

[[['a'],[24],214,1] ,[['b'],[24],312,1] ,[['a'],[24],3124,1] , [['c'],[24],34,1]]

and suppose I want to remove from the list all the items EXCEPT the one that has the maximum value for item[2] among items sharing the same letter in item[0]

So for example in the previous list I have two items sharing the same letter in item[0]:

[ ['a'],[24],214,1], [['a'],[24],3124,1] ]

and I want to remove the former since it has a lower value for item[2].

The output list should then be:

[ [['b'],[24],312,1] ,[['a'],[24],3124,1] , [['c'],[24],34,1] ]

Can you suggest me a compact way to do it?

Answer 1

As your question is confusing, I have given the possibility of removing both the max and the min elements

>>> def foo(some_list, fn = max):
    #Create a dictionary, default dict won;t help much as 
    #we have to refer back to the value for an existing key
    #The dictionary would have item[0] as key
    foo_dict = dict()
    #Iterate through the list
    for e in some_list:
            #Check if the key exist
        if e[0][0] in foo_dict:
                    #and if it does, find the max of the existing value and the 
                    #new element. The key here is the second item
            foo_dict[e[0][0]] = fn(foo_dict[e[0][0]], e, key = lambda e:e[2])
        else:
                    #else consider the new element as the current max
            foo_dict[e[0][0]] = e
    return foo_dict.values()

>>> foo(somelist)
[[['a'], [24], 3124, 1], [['c'], [24], 34, 1], [['b'], [24], 312, 1]]
>>> foo(somelist,min)
[[['a'], [24], 214, 1], [['c'], [24], 34, 1], [['b'], [24], 312, 1]]