Thanks Richard and the others who responded to my query.
I truly appreciate you taking the time and effort to respond to me (and the
community) with your thoughts.
I had been reading about recursion, and was thinking only of that approach
to solve this.
My main reson for looking into Haskell is
Christopher Tauss schrieb:
I am a professional programmer with 11 years experience, yet I just do
not seem to be able to get the hang of even simple things in Haskell. I
am trying to write a function that takes a list and returns the last n
elements.
Looking through the glasses of lazy
2010/9/18 Daniel Fischer daniel.is.fisc...@web.de
n_lastn n = reverse . take n . reverse
Which is the most elegant definition, but it's an O(length list) space
operation (as are all others proposed so far). T
No!. You forget laziness!. it is 0(n) with n= the parameter passed to
Luke Palmer schrieb:
I think this is O(n) time, O(1) space (!).
lastk :: Int - [a] - [a]
lastk k xs = last $ zipWith const (properTails xs) (drop k xs)
where properTails = tail . tails
If (drop k xs) is empty, this yields an error when calling 'last'. This
might be a bug or a feature.
Hi Alberto,
On 20.09.2010, at 10:53, Alberto G. Corona wrote:
2010/9/18 Daniel Fischer daniel.is.fisc...@web.de
n_lastn n = reverse . take n . reverse
Which is the most elegant definition, but it's an O(length list) space
operation (as are all others proposed so far). T
No!. You
On Sep 20, 2010, at 5:10 AM, Jean-Marie Gaillourdet wrote:
Hi Alberto,
On 20.09.2010, at 10:53, Alberto G. Corona wrote:
2010/9/18 Daniel Fischer daniel.is.fisc...@web.de
n_lastn n = reverse . take n . reverse
Which is the most elegant definition, but it's an O(length list) space
Hi James,
On 20.09.2010, at 15:20, James Andrew Cook wrote:
Lazyness helps helps to reduce work if your input list is lazily constructed
and your function forces the returned element. Then you don't have to force
all elements of the list, only the last one. Let's say l = [e_0, ..., e_n].
On Monday 20 September 2010 15:20:53, James Andrew Cook wrote:
On Sep 20, 2010, at 5:10 AM, Jean-Marie Gaillourdet wrote:
Hi Alberto,
On 20.09.2010, at 10:53, Alberto G. Corona wrote:
2010/9/18 Daniel Fischer daniel.is.fisc...@web.de
n_lastn n = reverse . take n . reverse
Have we put off the ultra-newbie by derailing his simple question into a
discussion on subtle issues he shouldn't care about this early on?
On Mon, Sep 20, 2010 at 3:49 PM, Daniel Fischer daniel.is.fisc...@web.dewrote:
On Monday 20 September 2010 15:20:53, James Andrew Cook wrote:
On Sep 20,
On Sep 20, 2010, at 9:49 AM, Daniel Fischer wrote:
which I am inclined to believe. Your 'f' should also run in O(1) space.
Alas, no. At least with GHC (and I don't see how it could be otherwise),
reverse is always an O(length xs) space operation.
reverse :: [a] - [a]
On Sep 18, 2010, at 7:51 PM, Christopher Tauss wrote:
Hello Haskell Community -
I am a professional programmer with 11 years experience, yet I just do not
seem to be able to get the hang of even simple things in Haskell. I am
trying to write a function that takes a list and returns the
I like this one!
Here's a variant using fold:
lastk :: Int - [a] - [a]
lastk k xs = foldl' (const.tail) xs (drop k xs)
or point free:
lastk = ap (foldl' (const. tail)). drop
Hallo Luke Palmer, je schreef op 18-09-10 22:42:
I think this is O(n) time, O(1) space (!).
lastk :: Int - [a] - [a]
Hello Haskell Community -
I am a professional programmer with 11 years experience, yet I just do not
seem to be able to get the hang of even simple things in Haskell. I am
trying to write a function that takes a list and returns the last n
elements.
There may be a function which I can just call
On 18 September 2010 17:51, Christopher Tauss ctau...@gmail.com wrote:
Hello Haskell Community -
I am a professional programmer with 11 years experience, yet I just do not
seem to be able to get the hang of even simple things in Haskell. I am
trying to write a function that takes a list and
Here is a more manual way to do it, hopefully this shows the approach
required. You don't need to store anything, just keep removing the
head of the list until its of the size you want.
n_lastn :: Int - [a] - [a]
n_lastn n xs =
let len = length xs - n
drp = if len 0 then 0 else len
Am 18.09.2010 09:51, schrieb Christopher Tauss:
I am trying to write a function that takes a list and returns the last n
elements.
last_n n = fst . foldr step ([], n)
where
step _ (xs, 0) = (xs, 0)
step x (xs, n) = (x:xs, n-1)
___
On 09/18/2010 02:51 AM, Christopher Tauss wrote:
I am trying to write a function that takes a list and returns the last n
elements.
This may just be for the sake of learning, in which case this is fine,
but usually, needing to do this would be a sign that you are using lists
improperly
Thanks you Ivan and David for clarifying this.
Best Regards,
Chris
On Sat, Sep 18, 2010 at 3:55 AM, Ivan Lazar Miljenovic
ivan.miljeno...@gmail.com wrote:
On 18 September 2010 17:51, Christopher Tauss ctau...@gmail.com wrote:
Hello Haskell Community -
I am a professional programmer
On Saturday 18 September 2010 19:44:38, Jake McArthur wrote:
On 09/18/2010 02:51 AM, Christopher Tauss wrote:
I am trying to write a function that takes a list and returns the last
n elements.
This may just be for the sake of learning, in which case this is fine,
but usually, needing to do
I think this is O(n) time, O(1) space (!).
lastk :: Int - [a] - [a]
lastk k xs = last $ zipWith const (properTails xs) (drop k xs)
where properTails = tail . tails
Luke
On Sat, Sep 18, 2010 at 1:51 PM, Daniel Fischer
daniel.is.fisc...@web.de wrote:
On Saturday 18 September 2010 19:44:38,
On Saturday 18 September 2010 22:42:57, Luke Palmer wrote:
I think this is O(n) time, O(1) space (!).
lastk :: Int - [a] - [a]
lastk k xs = last $ zipWith const (properTails xs) (drop k xs)
where properTails = tail . tails
Luke
No, it's O(k) too. You zip [[x_n, x_{n+1}, ... ], ... ]
On Sep 18, 2010, at 12:51 AM, Christopher Tauss wrote:
I am a professional programmer with 11 years experience, yet I just
do not seem to be able to get the hang of even simple things in
Haskell. I am trying to write a function that takes a list and
returns the last n elements.
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