duplicate items in a list

[Shi Mu]

I used the following method to remove duplicate items in a list and
got confused by the error.
[color=blue][color=green][color=darkred]
>>> a[/color][/color][/color]
[[1, 2], [1, 2], [2, 3]][color=blue][color=green][color=darkred]
>>> noDups=[ u for u in a if u not in locals()['_[1]'] ][/color][/color][/color]
Traceback (most recent call last):
File "<interacti ve input>", line 1, in ?
TypeError: iterable argument required

[Daniel Schüle]

Re: duplicate items in a list

Shi Mu wrote:[color=blue]
> I used the following method to remove duplicate items in a list and
> got confused by the error.
>
>[color=green][color=darkred]
>>>>a[/color][/color]
>
> [[1, 2], [1, 2], [2, 3]]
>[color=green][color=darkred]
>>>>noDups=[ u for u in a if u not in locals()['_[1]'] ][/color][/color]
>
> Traceback (most recent call last):
> File "<interacti ve input>", line 1, in ?
> TypeError: iterable argument required[/color]
[color=blue][color=green][color=darkred]
>>> a[/color][/color][/color]
[[1, 2], [1, 2], [2, 3]][color=blue][color=green][color=darkred]
>>> c=[]
>>> for x in a:[/color][/color][/color]
.... if x not in c: c.append(x)
....[color=blue][color=green][color=darkred]
>>> c[/color][/color][/color]
[[1, 2], [2, 3]]

or (Python 2.4)

[color=blue][color=green][color=darkred]
>>> a[/color][/color][/color]
[[1, 2], [1, 2], [2, 3]][color=blue][color=green][color=darkred]
>>> set([frozenset(u) for u in a])[/color][/color][/color]
set([frozenset([1, 2]), frozenset([2, 3])])

hth Daniel

[Daniel Schüle]

Re: duplicate items in a list

Shi Mu wrote:[color=blue]
> I used the following method to remove duplicate items in a list and
> got confused by the error.
>
>[color=green][color=darkred]
>>>>a[/color][/color]
>
> [[1, 2], [1, 2], [2, 3]]
>[color=green][color=darkred]
>>>>noDups=[ u for u in a if u not in locals()['_[1]'] ][/color][/color]
>
> Traceback (most recent call last):
> File "<interacti ve input>", line 1, in ?
> TypeError: iterable argument required[/color]
[color=blue][color=green][color=darkred]
>>> a[/color][/color][/color]
[[1, 2], [1, 2], [2, 3]][color=blue][color=green][color=darkred]
>>> c=[]
>>> for x in a:[/color][/color][/color]
.... if x not in c: c.append(x)
....[color=blue][color=green][color=darkred]
>>> c[/color][/color][/color]
[[1, 2], [2, 3]]

or (Python 2.4)

[color=blue][color=green][color=darkred]
>>> a[/color][/color][/color]
[[1, 2], [1, 2], [2, 3]][color=blue][color=green][color=darkred]
>>> set([frozenset(u) for u in a])[/color][/color][/color]
set([frozenset([1, 2]), frozenset([2, 3])])

hth Daniel

[Steven D'Aprano]

Re: duplicate items in a list

On Mon, 21 Nov 2005 02:49:56 -0800, Shi Mu wrote:
[color=blue]
> I used the following method to remove duplicate items in a list and
> got confused by the error.
>[color=green][color=darkred]
>>>> a[/color][/color]
> [[1, 2], [1, 2], [2, 3]][color=green][color=darkred]
>>>> noDups=[ u for u in a if u not in locals()['_[1]'] ][/color][/color]
> Traceback (most recent call last):
> File "<interacti ve input>", line 1, in ?
> TypeError: iterable argument required[/color]

Confused by the error? I'm confused by your code!!!

If you want to remove duplicate items in a list, try something like this:


def remove_dups(L):
"""Removes duplicate items from list L in place."""
# Work backwards from the end of the list.
for i in range(len(L)-1, -1, -1):
# Check to see if the current item exists elsewhere in
# the list, and if it does, delete it.
if L[i] in L[:i]:
del L[i]

Instead of deleting duplicate items in place, we can create a new list
containing just the unique items:

def unique_items(L) :
"""Returns a new list containing the unique items from L."""
U = []
for item in L:
if item not in U:
U.append(item)
return U


The trick you are trying to do with _ is undocumented and, even if you get
it to work *now*, is probably not going to work in the future. Don't do it.


--
Steven.

[Steven D'Aprano]

Re: duplicate items in a list

On Mon, 21 Nov 2005 02:49:56 -0800, Shi Mu wrote:
[color=blue]
> I used the following method to remove duplicate items in a list and
> got confused by the error.
>[color=green][color=darkred]
>>>> a[/color][/color]
> [[1, 2], [1, 2], [2, 3]][color=green][color=darkred]
>>>> noDups=[ u for u in a if u not in locals()['_[1]'] ][/color][/color]
> Traceback (most recent call last):
> File "<interacti ve input>", line 1, in ?
> TypeError: iterable argument required[/color]

Confused by the error? I'm confused by your code!!!

If you want to remove duplicate items in a list, try something like this:


def remove_dups(L):
"""Removes duplicate items from list L in place."""
# Work backwards from the end of the list.
for i in range(len(L)-1, -1, -1):
# Check to see if the current item exists elsewhere in
# the list, and if it does, delete it.
if L[i] in L[:i]:
del L[i]

Instead of deleting duplicate items in place, we can create a new list
containing just the unique items:

def unique_items(L) :
"""Returns a new list containing the unique items from L."""
U = []
for item in L:
if item not in U:
U.append(item)
return U


The trick you are trying to do with _ is undocumented and, even if you get
it to work *now*, is probably not going to work in the future. Don't do it.


--
Steven.