How to use certain elements in a list to compare elements in other lists and output a certain element if duplicates are found in Python?

Question

I am new here (and new to programming). I have tried to locate the relevant questions with no luck.

Basically, I got some lists shown below:

[0, 'a', 1, 3, 3.3, 220, 22.27]
[0, 'b', 1, 13, 3.3, 220, 23.19]
[0, 'c', 1, 23, 3.3, 220, 24.11]
[1, 'a', 1, 3, 3.5, 200, 20.02]
[1, 'b', 1, 43, 3.3, 220, 25.94]
[2, 'a', 1, 3, 3.3, 250, 26.86]

I would like to use list items of indices 1, 2 and 3 as the comparison key and search within all the lists available with the given key.

If found, then I need it the output to be made up of the list items of indices 0, 4, 5 and -1.

So, with the given lists, the desired procedure is shown below.

First round:

comparison key : 'a', 1, 3
go through the available lists
found the same key in

[0, 'a', 1, 3, 3.3, 220, 22.27]

[1, 'a', 1, 3, 3.5, 200, 20.02]

[2, 'a', 1, 3, 3.3, 250, 26.86]
then create the output

0, 3.3, 220, 22.27

1, 3.5, 200, 20.02

2, 3.3, 250, 26.86

I have no idea how to code this yet, so could anyone help me please?

Thanks in advance

What have you tried so far? Please provide any code you got so far. Are you looking for groups of three, only? — albert, Jul 21 '16 at 16:48
I would try to break this problem down a bit conceptually and then build each part up in sections. 1. You want to be able to search a list to see if it contain a subset 2. You want to be able remove a subset if it is contained in a list 3. You want to run this filter over multiple lists 4. You want to print the output of a set of lists. Try solving the parts individually and then combine the individual parts to form the full solution — Selecsosi, Jul 21 '16 at 16:51

score 0 · Accepted Answer · answered Jul 21 '16 at 16:55

@wagaman: Hi Pal, Here a little snippet to do this job:

universe = []
universe.append([0, 'a', 1, 3, 3.3, 220, 22.27])
universe.append([0, 'b', 1, 13, 3.3, 220, 23.19])
universe.append([0, 'c', 1, 23, 3.3, 220, 24.11])
universe.append([1, 'a', 1, 3, 3.5, 200, 20.02])
universe.append([1, 'b', 1, 43, 3.3, 220, 25.94])
universe.append([2, 'a', 1, 3, 3.3, 250, 26.86])


def extract_from_lists(universe, keys=[1,2,3], matches=['a',1,3]):
    if len(keys) == len(matches):
        for l in universe:
            valid = True
            for i in range(len(keys)):
                if l[keys[i]] != matches[i]:
                    valid = False
                    break
            if valid:
                print("{},{},{},{}".format(l[0],l[4],l[5],l[-1]))
    else:
        print('Keys List and Matches List length must be equal.')


extract_from_lists(universe)

If you need further information about it, let me know, it's a very simple comparison and use basic concepts of python as default values of arguments, iteration and so.

score 0 · Answer 2 · edited May 23 '17 at 12:32

Let us first define the input data:

some_lists = [[0, 'a', 1, 3, 3.3, 220, 22.27],
              [0, 'b', 1, 13, 3.3, 220, 23.19],
              [0, 'c', 1, 23, 3.3, 220, 24.11],
              [1, 'a', 1, 3, 3.5, 200, 20.02],
              [1, 'b', 1, 43, 3.3, 220, 25.94],
              [2, 'a', 1, 3, 3.3, 250, 26.86]]

We have to iterate over the sublists of some_lists. To that end we will use an index variable, say x. For each sublist x we need to check whether x[1] == 'a' and x[2] == 1 and x[3] == 3 is fulfilled or not. This logical expression can be simplified through slice notation to x[1:4] == ['a', 1, 3]. For those x that match the condition, we create the desired output by selecting the specified items, namely [x[0], x[4], x[5], x[-1]]. All this logic can be readily implemented through a list comprehension in just one line of code:

In [253]: [[x[0], x[4], x[5], x[-1]] for x in some_lists if x[1:4] == ['a', 1, 3]]              
Out[253]: [[0, 3.3, 220, 22.27], [1, 3.5, 200, 20.02], [2, 3.3, 250, 26.86]]

How to use certain elements in a list to compare elements in other lists and output a certain element if duplicates are found in Python?

2 Answers2