[Rd] proposal for lower.tri and upper.tri value argument

[Prof Brian Ripley]

Is there a case to be made for this?  If so, where is it?

(I don't find x[lower.tri(x)] harder to write than lower.tri(x, 
value=TRUE), and wonder why you do?  For grep, one can argue that handling 
empty sets is clearer with value=, but I have seen quite a few uses where 
that is not used and could have been.)

On Sat, 5 Aug 2006, Patrick Burns wrote:

> I propose that a 'value' argument be added to
> 'lower.tri' and 'upper.tri'.  This is analogous to
> the 'value' argument of 'grep'.
> 
> Something like the following should work:
> 
>  > upper.tri
> function (x, diag = FALSE, value = FALSE)
> {
>     x <- as.matrix(x)
>     if (diag)
>         ans <- row(x) <= col(x)
>     else ans <- row(x) < col(x)
>     if(value) x[ans] else ans
> }
> <environment: namespace:base>

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595