CODEWITHSUNDEEP
pythonpython-3.xset
virmis_007
virmis_007

Reputation: 173

Delete last element of set in python

How can I delete the last element of a set, or create a new set without last element? Sets do not support indexing. I have a set of integers, and want to remove the largest.

Upvotes: 2

Views: 13192

Answers (4)

Prune
Prune

Reputation: 77850

You can remove any specified element with the remove method:

>>> s = {3, 'a', True}
>>> s
{'a', True, 3}
>>> s.remove(3)
>>> s
{'a', True}

However, any concept of "last" must come from beyond the set itself, since a set does not implement the idea of a fixed order. Note the difference above between the assigned value and the printed value.

Update after OP clarification

To remove the numerically largest element of the set:

s.remove(max(s))

You commented:

if a set contains only integers, then the elements are by default listed in ascending order.

This is incorrect. For example:

>>> lll = [3**n for n in range(10)]
>>> sss = set(lll)
>>> sss
{1, 6561, 3, 19683, 9, 2187, 81, 243, 729, 27}

Perhaps you're confused by some of the effects of small integers in Python. The integer constants up to (usually) 256 are pre-allocated by the run-time system, stored in numerical order in memory, with special hash handling. One effect of this is that their hash values are in order. Once you go beyond that range, the hashing is different, as seen above:

Upvotes: 5

maor10
maor10

Reputation: 1784

As everyone here has said, sets are unordered, but if you want to remove an element from the set you could do the following (let's call the set a_set):

a_set = set(list(a_set)[:-1])

I want to make it clear- you're not removing the last element of the set, because there is no such thing, but you're converting it to a list, removing the last element, then converting back

Upvotes: 0

Hermis14
Hermis14

Reputation: 204

The sets are unordered collections. Refer to https://docs.python.org/3/tutorial/datastructures.html#sets. Try using List instead to do what you intended. Then variable.pop(0) method will do the job.

Upvotes: 0

Kenan
Kenan

Reputation: 14104

I don't think you can do that since there is no last element of a set. As you can see from the documentation https://docs.python.org/2/library/sets.html, sets are unordered.

Upvotes: 0

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