[R] matrix from list

Olivier Lefevre lefevrol at yahoo.com
Sat Apr 26 17:53:05 CEST 2008

Martin Maechler wrote:
>   The difference to as.matrix() is that data.matrix() also
>   produces a numeric matrix in the case the data frame contains
>   factors.

Thanks, that is useful but it is becoming a little rococo: so may ways to 
do this. Also, what if I have a list, not a data frame? read.table returns 
a data frame but a select from a spreadsheet (via RODBC) returns a list.

> - I don't understand why you want to throw away the dimnames of
>   the resulting numeric matrix.  Rather, in general you'd want
>   to keep them.

Merely because I find it confusing. When printing, which you do a lot of 
when developing in interactive languages like R, list and as.matrix(list) 
look absolutely the same, which is irksome and confusing since you have to 
resort to mode to check what you've got, under penalty of strange errors 
farther down. So I stick to the convention of unattributed matrices and 
arrays in my code: that way it's easy to know which is which.


-- O.L.

More information about the R-help mailing list