Sort List of Lists of Lists Python

Question

I have a List of Lists of Lists in python. I need to sort the highest level of lists based on one of the values in the lowest levels.

For a toy model, my list is created first with list small, which is a list containing lists with three items each:

    small = [["dog", 5, 6], ["cat", 391, 130], ["pig", 45, 2]...]`

Then there is a larger list, large, that is created by appending the small list and another item together:

    large.append([["category 1"], small])`

This is done in a loop, so if the loop has a counter of 5, it will proceed through a function that creates a list small 5 times, each time, appending it to list large.

My goal is to sort the final list based on an element in the smallest list (the list that comprises the small list). I am currently printing the large list out line by line, with the small list ordered by the index 1 of the lists within it (see: 5,10,15 in order, 1,3,6 in order, etc), so my output is this:

    >category 1:
    >['Dog', 5, 6]
    >['Pig', 10, 2]
    >['Cat', 15, 130]
    >['Buffalo', 20, 1]
    >['Newt', 25, 45]

    >category 2:
    >['Newt', 1, 1092]
    >['Cat', 3, 352]
    >['Pig', 6, 34]
    >['Buffalo', 9, 12]
    >['Dog', 12, 5]

    >category 3:
    >['Buffalo', 2, 12]
    >['Pig', 4, 37]
    >['Cat', 6, 34]
    >['Newt', 8, 150]
    >['Dog', 10, 52]

However, i would like to print the large list in order of smallest to largest when looking at the element in index 1 in the list that makes up the smallest array. So my ideal output would be this:

    >category 2:
    >['Newt', 1, 1092]
    >['Cat', 3, 352]
    >['Pig', 6, 34]
    >['Buffalo', 9, 12]
    >['Dog', 12, 5]

    >category 3:
    >['Buffalo', 2, 12]
    >['Pig', 4, 37]
    >['Cat', 6, 34]
    >['Newt', 8, 150]
    >['Dog', 10, 52]

    >category 1:
    >['Dog', 5, 6]
    >['Pig', 10, 2]
    >['Cat', 15, 130]
    >['Buffalo', 20, 1]
    >['Newt', 25, 45]

I have tried sorting with itemgetter(), however, when sorting large with itemgetter(), i can only sort the items in list large, which are [category x] and [[a,b,c], [a,b,c]]. Is there a way to access the lowest level of elements for itemgetter? or another way to go about sorting this list?

Thanks.

Answer 1

This can be done in one line:

sorted_large = sorted(large, key=lambda item: item[1][0][1])

The sorted built-in function takes a key parameter:

key specifies a function of one argument that is used to extract a comparison key from each list element

Using a lambda expression, the sorting key can be extracted.