seq_along and rep_along

Hi all,

A couple of ideas for improving seq_along:

* It would be really useful to have a second argument dim:

     seq_along(mtcars, 1)
     seq_along(mtcars, 2)
     # equivalent to
     seq_len(dim(mtcars)[1])
     seq_len(dim(mtcars)[2])

   I often find myself wanting to iterate over the rows or column of a
data frame, and there isn't a particularly nice idiom if you want to
avoid problems with zeros - you have to use seq_len(nrow(df)) etc

* To me, it would seem be very natural to have a rep_along function:

   rep_along<- function(x, y) rep(x, length.out = length(y))

   possibly with more checking for the case where the lengths aren't
integer multiples.

I'd be happy to submit proposed implementations/documentation if there
was interest.

Hadley

I don't see the benefit of seq_along(mtcars, 1) versus seq_len(nrow(df)) in
readability.

but it is frustrating when base
functionality only works with vectors, not matrices, or arrays. It
would be more compelling if (e.g.) t and rev also had dimension
arguments.

Hadley

--

Assistant Professor / Dobelman Family Junior Chair
Department of Statistics / Rice University
http://had.co.nz/

well put! ?I would add, though, that t() generalizes to aperm(),
and the magic package contains ?arev() ?which is a generalization
of rev().

I'm always on the lookout for other array functionality of this type
that might sit well with magic. ?Anyone?

There are the flip operators of matlab, and rotating matrices/array by
multiples of 90 degrees.

I'm always on the lookout for other array functionality of this type
that might sit well with magic. ?Anyone?

Have you considered pulling out the matric manipulation functions from
magic? ?I think they'd do well in their own package, and would be more
findable.

Hadley

--
Assistant Professor / Dobelman Family Junior Chair
Department of Statistics / Rice University
http://had.co.nz/