Re: list to array conversion?

["G. Milde" <g.milde@xxxxxx>]

On 12.04.06, John E. Davis wrote:
> Marko Mahnic <marko.mahnic@xxxxxxxx> wrote:
> >Maybe there could be a where() version for lists:
> >
> >   where([DataType_Type type,] condition)
> >
> >? It would only perform a test on a certain type of elements.
> 
> I eventually plan to extend the comparison operators to lists.  Then
> you would be able to do something like:
> 
>     i = where (list > 3);
> For this to be useful, list[i] should return a "sublist".  

Slicing via array args as e.g. liste[[1:3]] would indeed be a very nice
feature, not only for where() results. 

(This slicing notation is even more powerfull than the one used in
Python, as it allows "arbitrary spare" sublists|subarrays as with
liste[[1,4,5,22]].)

> Of course this will not work if a list consists of datatypes where the
> comparison makes no sense.  For this reason, my inclination would be to
> throw an exception if a comparison were made on a list containing such
> elements.

However, one could consider extending the `case' like comparision, say a
function wherecase(container, comparator), where

     wherecase({0,1,2,3,"vier",5,2}, 2)
   
would return [2,6] instead of throwing an exception. It should also work
for Any_Type arrays.

And how about a list_map() alongside array_map() or maybe a map()
replacing both?

Guenter

-- 
Milde ife.et.tu-dresden.de

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