Re: [Gretl-devel] Small bug
On Thu, 5 May 2011, Sven Schreiber wrote:
Am 05.05.2011 07:32, schrieb Marcin Błażejowski:
> Hi,
> simple script:
>
> <script>
> set echo off
> set messages off
>
> function void FOO (matrix mat)
> printf "%d\n", nelem(mat)
> end function
>
> nulldata 10
>
> matrix foo = zeros(2,1)
> FOO(foo)
>
> foo[1,1] = 1
> FOO(foo)
> </script>
>
> In both situations we get what we excpect: 2
I'm surprised it works at all, according to the docs nelem() is only for
lists, not for matrices.
Sven is right: in concept, nelem() is only for lists. For
matrices, use rows() or cols(). However, to facilitate
manipulating lists, it's possible to "cast" from a (suitable)
matrix to a list, where a suitable matrix is a vector containing
nothing but non-negative integers.
What's happening here is that Marcin's matrix looks OK as a
representation of a list, but if it's interpreted that way then in
the second case it references the non-existent series 2.
I think it might be better (to avoid confusing error messages) to
modify "genr" so that the cast from a matrix to a list must be
done explicitly. In that case you'd get a "non-conformable types"
error if you try using nelem() on any object that's not already
defined as a list.
Allin