Op woensdag 30 april 2014 09:58:26 UTC+2 schreef James Reeves:
>
> On 30 April 2014 07:49, Roelof Wobben <rwo...@hotmail.com <javascript:>>wrote:
>>
>>
>> Op woensdag 30 april 2014 08:21:40 UTC+2 schreef James Reeves:
>>
>>>
>>> 1. How do you find the last element of a seq with exactly one element?
>>>
>>
>> the last and the first element are the same
>>
>
> Right. So to formalise it:
>
> (defn last* [coll]
> (first coll))
>
> I'm using "last*" as the name so that it doesn't conflict with the
> function "last" in clojure.core.
>
>
> 2. How do you find out whether a seq has one element, or more than one
>>> element?
>>>
>>
>> Look at the length of the seq
>>
>
> Unlike vectors, seqs are simple structures and don't know their own length.
>
> You can count seqs, but this involves iterating through every element in
> turn. If all you want to do is find out whether there is more than one
> element, there's a much simpler and more efficient way.
>
>
>
Yep, if there is only 1 item is a list (rest coll) is nil.
> In code, this would be:
>
> (defn last* [coll]
> (if (more-than-one-element? coll)
> (first (rest coll))
> (first coll)))
>
> The "more-than-one-element?" to be replaced with the answer to question 2,
> of course.
>
> Can you think of a way of making this function recursive to work with any
> number of elements?
>
I think I can but I have to try some things but untested it looks like this
(defn last* [coll]
(if (nil? (rest coll)
(first coll)))
> (last* (rest coll))
>
Now I wonder how I can make it work if I want to find lets say the 5th
value of a array of any number of elements
Then rest is never nil. So at first glance if I do not know the length it
cannnot be done recursive.
I have to do it in a for loop.
> - James
>
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