Re: [Tutor] Need help combining elements of a list of lists
On 07/10/2018 11:03 PM, Mats Wichmann wrote:
On 07/10/2018 09:09 PM, Steven D'Aprano wrote:
On Tue, Jul 10, 2018 at 09:46:57PM -0500, Jim wrote:
Say I have a list like ltrs and I want to print out all the possible 3
letter combinations. I want to combine letters from each inner list but
not combine any letters within the inner list itself. So ACF and ADF
would be ok but ABC would not.
I can lay it out manually and see the pattern, I cannot figure out how
to do it programically. Just in case this looks like homework it is not.
It's a small test case I devised to try to figure it out so I can apply
it to a bigger real world problem I am working on.
ltrs = [['A', 'B'], ['C', 'D', 'E'], ['F', 'G', 'H', 'I']]
If you know that there are just three sublists, then you can do this:
for a in ltrs[0]:
for b in ltrs[1]:
for c in ltrs[2]:
print(a + b + c)
I trust that's easy enough to understand.
But here's a more general technique, where you don't need to know up
front how many nested lists there are:
from itertools import product # short for "Cartesian Product"
for s in product(*ltrs):
print(''.join(s))
This is one of those cases where: if it's homework, getting the nested
loops right is almost certainly the way to go. If it isn't, then
itertools (that is, "using an available library solution") is almost
certainly the way to go :)
If the eventual case is not just "letters", and a list of combined lists
is the eventual goal, then the concise stanza is:
prods = list(product(*ltrs))
print(prods) then gives you:
[('a', 'c', 'f'), ('a', 'c', 'g'), ('a', 'c', 'h'), ('a', 'c', 'i'),
('a', 'd', 'f'), ('a', 'd', 'g'), ('a', 'd', 'h'), ('a', 'd', 'i'),
('a', 'e', 'f'), ('a', 'e', 'g'), ('a', 'e', 'h'), ('a', 'e', 'i'),
('b', 'c', 'f'), ('b', 'c', 'g'), ('b', 'c', 'h'), ('b', 'c', 'i'),
('b', 'd', 'f'), ('b', 'd', 'g'), ('b', 'd', 'h'), ('b', 'd', 'i'),
('b', 'e', 'f'), ('b', 'e', 'g'), ('b', 'e', 'h'), ('b', 'e', 'i')]
if you want them concatenated, then of course join is the way to do that.
Steven & Mats thanks for your replies.
It is more that just letters. I was reading Al Sweigart's book Cracking
Codes with Python. I got to the chapter on substitution cyphers and
wondered if his program could solve the daily Crypto Quips in the
newspaper. Turns out it did not do a very good job because the quips
were to short.
It did produce a dictionary where the keys are the letters of the
alphabet and the items are a list of possible letters to substitute. If
a key has no possible letters it is ignored, if a key has only one
possible letter it considered a solution and plugged into the cypher.
the keys with multiple possible letters are ones I am interested in.
I know you cannot brute force a substitution cypher but maybe I could
loop over and combine the possible substitution letters and crack it
that way. That's why I made up the letter problem, I wanted to see how
to do it on a simple data set before attempting much more complex one.
It looks like the library solution is the way for me to try.
Regards, Jim
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Re: [Tutor] Need help combining elements of a list of lists
On 07/10/2018 10:09 PM, David Rock wrote: On Jul 10, 2018, at 22:04, David Rock wrote: On Jul 10, 2018, at 21:46, Jim wrote: ltrs = [['A', 'B'], ['C', 'D', 'E'], ['F', 'G', 'H', 'I']] A fairly straightforward way is to use nested loops: for l in ltrs[0]: ... for j in ltrs[1]: ... for k in ltrs[2]: ... print l,j,k Sorry, let’s try to make that a little cleaner-looking for x in ltrs[0]: for y in ltrs[1]: for z in ltrs[2]: print x,y,z Seeing it in front of me it does look straight forward, I was having difficulty visualizing how to solve it. thanks, Jim ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Need help combining elements of a list of lists
On 07/10/2018 09:09 PM, Steven D'Aprano wrote:
> On Tue, Jul 10, 2018 at 09:46:57PM -0500, Jim wrote:
>
>> Say I have a list like ltrs and I want to print out all the possible 3
>> letter combinations. I want to combine letters from each inner list but
>> not combine any letters within the inner list itself. So ACF and ADF
>> would be ok but ABC would not.
>>
>> I can lay it out manually and see the pattern, I cannot figure out how
>> to do it programically. Just in case this looks like homework it is not.
>> It's a small test case I devised to try to figure it out so I can apply
>> it to a bigger real world problem I am working on.
>>
>> ltrs = [['A', 'B'], ['C', 'D', 'E'], ['F', 'G', 'H', 'I']]
>
> If you know that there are just three sublists, then you can do this:
>
> for a in ltrs[0]:
> for b in ltrs[1]:
> for c in ltrs[2]:
> print(a + b + c)
>
> I trust that's easy enough to understand.
>
> But here's a more general technique, where you don't need to know up
> front how many nested lists there are:
>
>
> from itertools import product # short for "Cartesian Product"
> for s in product(*ltrs):
> print(''.join(s))
This is one of those cases where: if it's homework, getting the nested
loops right is almost certainly the way to go. If it isn't, then
itertools (that is, "using an available library solution") is almost
certainly the way to go :)
If the eventual case is not just "letters", and a list of combined lists
is the eventual goal, then the concise stanza is:
prods = list(product(*ltrs))
print(prods) then gives you:
[('a', 'c', 'f'), ('a', 'c', 'g'), ('a', 'c', 'h'), ('a', 'c', 'i'),
('a', 'd', 'f'), ('a', 'd', 'g'), ('a', 'd', 'h'), ('a', 'd', 'i'),
('a', 'e', 'f'), ('a', 'e', 'g'), ('a', 'e', 'h'), ('a', 'e', 'i'),
('b', 'c', 'f'), ('b', 'c', 'g'), ('b', 'c', 'h'), ('b', 'c', 'i'),
('b', 'd', 'f'), ('b', 'd', 'g'), ('b', 'd', 'h'), ('b', 'd', 'i'),
('b', 'e', 'f'), ('b', 'e', 'g'), ('b', 'e', 'h'), ('b', 'e', 'i')]
if you want them concatenated, then of course join is the way to do that.
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Re: [Tutor] Need help combining elements of a list of lists
> On Jul 10, 2018, at 22:04, David Rock wrote: > >> On Jul 10, 2018, at 21:46, Jim wrote: >> >> ltrs = [['A', 'B'], ['C', 'D', 'E'], ['F', 'G', 'H', 'I']] > > A fairly straightforward way is to use nested loops: > for l in ltrs[0]: > ... for j in ltrs[1]: > ... for k in ltrs[2]: > ... print l,j,k > Sorry, let’s try to make that a little cleaner-looking for x in ltrs[0]: for y in ltrs[1]: for z in ltrs[2]: print x,y,z — David Rock da...@graniteweb.com ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Need help combining elements of a list of lists
On Tue, Jul 10, 2018 at 09:46:57PM -0500, Jim wrote:
> Say I have a list like ltrs and I want to print out all the possible 3
> letter combinations. I want to combine letters from each inner list but
> not combine any letters within the inner list itself. So ACF and ADF
> would be ok but ABC would not.
>
> I can lay it out manually and see the pattern, I cannot figure out how
> to do it programically. Just in case this looks like homework it is not.
> It's a small test case I devised to try to figure it out so I can apply
> it to a bigger real world problem I am working on.
>
> ltrs = [['A', 'B'], ['C', 'D', 'E'], ['F', 'G', 'H', 'I']]
If you know that there are just three sublists, then you can do this:
for a in ltrs[0]:
for b in ltrs[1]:
for c in ltrs[2]:
print(a + b + c)
I trust that's easy enough to understand.
But here's a more general technique, where you don't need to know up
front how many nested lists there are:
from itertools import product # short for "Cartesian Product"
for s in product(*ltrs):
print(''.join(s))
The *ltrs syntax might be a bit mysterious: it is called "sequence
unpacking", and tells the interpreter to use each item from ltrs as a
separate argument:
product(*ltrs)
=> product(ltrs[0], ltrs[1], ltrs[2])
--
Steve
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Re: [Tutor] Need help combining elements of a list of lists
> On Jul 10, 2018, at 21:46, Jim wrote: > > ltrs = [['A', 'B'], ['C', 'D', 'E'], ['F', 'G', 'H', 'I']] A fairly straightforward way is to use nested loops: >>> for l in ltrs[0]: ... for j in ltrs[1]: ... for k in ltrs[2]: ... print l,j,k A C F A C G A C H A C I A D F A D G A D H A D I A E F A E G A E H A E I B C F B C G B C H B C I B D F B D G B D H B D I B E F B E G B E H B E I Not the most elegant, but probably the easiest to follow. — David Rock da...@graniteweb.com ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
