Question

This query is somewhat related to this earlier one on sorting

where, it was required to sort the following list,

data = [[1, .45, 0], [2, .49, 2], [3, .98, 0], [4, .82, 1], [5, .77, 1], [6, .98, 2] ]

first by the values of the last member of the inner list like this way,

[[1, .45, 0], [3, .98, 0],[4, .82, 1], [5, .77, 1], [2, .49, 2], [6, .98, 2]]

and then sort within the sub-lists i.e. first sort the list with its last member as '0' using the middle member as the key, in descending order, then the sub-list with last member as '1' and so on.

Now, instead of first sorting by the values of the last member, I would like like to sort based upon the order of these elements present in an external list. i.e. if the external list is List_1

`List_1 = [2, 0, 1]`

Sorting should produce

[[2, .49, 2], [6, .98, 2] [1, .45, 0], [3, .98, 0], [4, .82, 1], [5, .77, 1]]

Finally, sorting the sub-lists based upon the middle element in descending order should produce:

[ [6, .98, 2],[2, .49, 2],   [3, .98, 0], [1, .45, 0], [4, .82, 1], [5, .77, 1]]

Any suggestions on how to go about this ?

Answer 1

Use list.index in the key:

>>> data = [[1, .45, 0], [2, .49, 2], [3, .98, 0], [4, .82, 1],
            [5, .77, 1], [6, .98, 2]]
>>> List_1 = [2, 0, 1]
>>> sorted(data, key=lambda e: (List_1.index(e[2]), -e[1]))
[[6, 0.98, 2], [2, 0.49, 2], [3, 0.98, 0], [1, 0.45, 0],
 [4, 0.82, 1], [5, 0.77, 1]]