Re: [Gretl-users] saving the row/col names of a matrix
On Tue, 1 Nov 2011, artur bala wrote:
Another point (which was my original one): the [column or row]
names are not saved when a matrix is returned from a function.
True. Here's a minimal case:
<hansl>
function matrix mnames (void)
matrix m = I(3)
colnames(m, "col1 col2 col3")
print m
return m
end function
matrix m = mnames()
print m
</hansl>
Initially I thought this might be a simple bug that could easily be
fixed, but actually it turns out it's a design issue (and hence I'm
copying gretl-devel, hoping for comments).
The point is that the gretl_matrix type knows nothing about column
or row names. These names reside at the level of the "user_matrix"
struct which wraps a locally named gretl_matrix for ease of use. But
when a function returns a matrix, it returns a plain gretl_matrix:
the names are destroyed and not returned.
The main reason that the names are attached to the "user_matrix"
wrapper and not the gretl_matrix itself is to keep the gretl_matrix
type lean and mean. After all, it's used internally in many contexts
where column/row names are never wanted, and it's also offered as a
type for matrix operations by third parties (the libgretl API)
where, again, name-pointers are likely to be just a deadweight.
On the other hand, I can see a use-case for wanting to return a
matrix from a user-defined function with row and/or column names
attached. Right now, I'm not sure how to resolve this.
Allin