I am trying to translate this elegant Erlang-code for finding all the
permutations of a list.
I think it is the same function as is but it doesn't work in Python.
-- is upd in Python. It works as it should.
perms([]) -[[]];
perms(L) -[[H|T] || H <- L, T <- perms(L--[H])].
def perms(lista):
if lista == []:
return [[]]
else:
for h in lista:
return [([h]+[t]) for t in perms(upd(lista, h))]
def upd(lista, elem, acc=tuple([])):
lista = tuple(lista)
if lista == ():
return list(acc)
if lista[0] == elem:
return list(acc + tuple(lista[1:]))
else:
return upd(lista[1:], elem, acc + tuple([lista[0]])) 2 883
Hi,
Here's a (better?) function:
def permutate(seq):
if not seq:
return [seq]
else:
temp = []
for k in range(len(seq)):
part = seq[:k] + seq[k+1:]
for m in permutate(part):
temp.append(seq[k:k+1] + m)
return temp
cheers
James
On Mon, Sep 8, 2008 at 6:47 AM, cnb <ci**********@yahoo.sewrote:
I am trying to translate this elegant Erlang-code for finding all the
permutations of a list.
I think it is the same function as is but it doesn't work in Python.
-- is upd in Python. It works as it should.
perms([]) -[[]];
perms(L) -[[H|T] || H <- L, T <- perms(L--[H])].
def perms(lista):
if lista == []:
return [[]]
else:
for h in lista:
return [([h]+[t]) for t in perms(upd(lista, h))]
def upd(lista, elem, acc=tuple([])):
lista = tuple(lista)
if lista == ():
return list(acc)
if lista[0] == elem:
return list(acc + tuple(lista[1:]))
else:
return upd(lista[1:], elem, acc + tuple([lista[0]]))
-- http://mail.python.org/mailman/listinfo/python-list
--
--
-- "Problems are solved by method"
cnb <ci**********@yahoo.sewrites:
perms([]) -[[]];
perms(L) -[[H|T] || H <- L, T <- perms(L--[H])].
I think the most direct transcription might be:
def perms(xs):
if len(xs)==0: return [[]]
return [([h]+t) for h in xs
for t in perms([y for y in xs if y not in [h]])]
But it is rather inefficient, as is the Erlang version. This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics
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