From maechler at lynne.stat.math.ethz.ch  Mon May 18 14:14:04 2015
From: maechler at lynne.stat.math.ethz.ch (Martin Maechler)
Date: Mon, 18 May 2015 14:14:04 +0200
Subject: [Rd] \alias{} --> rather \concept{} for conceptual "links" to help
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>From R-help, subject  "Variable number of loops"
I've opened a new thread, moving from R-help to R-devel ..

>>>>> Jim Lemon <drjimlemon at gmail.com>
>>>>>     on Sun, 17 May 2015 09:19:06 +1000 writes:

    > Hi all, Given the number of help requests that involve
    > permutations/combinations, and the less than obvious
    > naming of the expand.grid function, perhaps adding an
    > alias such as "permute.elements" or "combine.elements"
    > might ease the tasks of both searchers and those offering
    > help. Neither of the above names appear to be used at
    > present.

    > Jim


Using \alias{} is not a very good thing here, since as you know they
are *key*s that must remain unique if possible and they can be
linked to -- which I think would not be helpful for  'expand.grid'.

Rather, for quite a few years now, we have had \concept{} for
adding "search keywords", i.e., things that 
help.search()  and hence ??<topic>  will find.

The other advantage of \concept{} is that you can use short
phrases, i.e., 

\concept{all variable combinations}

would be possible here.

(Better wording proposals for this specific case are welcome! --
 maybe privately).

Martin Maechler, ETH Zurich


    > On Sun, May 17, 2015 at 5:54 AM, Bert Gunter
    > <gunter.berton at gene.com> wrote:
    >> 1. Please always reply to the list unless there is a
    >> compelling reason to keep the discussion private. You
    >> will have a better chance of getting something useful
    >> that way.
    >> 
    >> 2. I don't know what you mean by "I don't have a fixed
    >> number of variables." You have to specify at least the
    >> number of variables and how many levels each has in order
    >> to work out what you requested, which is **NOT** the
    >> number of permutations but the number of combinations
    >> AFAICS, which is exactly what expand.grid will give you.
    >> 
    >> 3. Maybe what you're looking for is the ... arguments in
    >> function calls, which would be used along the lines of:
    >> 
    >> myfun <- function( x,y,...)  { ## some code combs <-
    >> expand.grid(...)  ## some more code }
    >> 
    >> Any good R tutorial will tell you about this if this is
    >> unfamiliar.
    >> 
    >> 4. Another possibility might be to deliver a list of
    >> named variables as an argument and then use do.call, e.g.
    >> 
    >> myfun <- (x,y, alist) { ## some code combs <-
    >> do.call(expand.grid, alist) ## some more code }
    >> 
    >> ?do.call and/or a tutorial for details.
    >> 
    >> 5. Otherwise, maybe someone else can figure out what
    >> you're looking for.
    >> 
    >> Cheers, Bert
    >> 
    >> 
    >> 
    >> Bert Gunter Genentech Nonclinical Biostatistics (650)
    >> 467-7374
    >> 
    >> "Data is not information. Information is not
    >> knowledge. And knowledge is certainly not wisdom."
    >> Clifford Stoll
    >> 
    >> 
    >> 
    >> 
    >> On Sat, May 16, 2015 at 11:16 AM, WRAY NICHOLAS
    >> <nicholas.wray at ntlworld.com> wrote:
    >>> I might be but doesn't expand.grid need a defined and
    >>> listed number of inputs?  The problem I'm having is that
    >>> the number of variables is not fixed, so I'm not sure
    >>> whether I can reference the variable number of variables
    >>> by using a vector -- haven't had time to try yet But
    >>> thanks anyway Nick Wray
    >>> 
    >>> On 16 May 2015 at 14:28, Bert Gunter
    >>> <gunter.berton at gene.com> wrote:
    >>>> 
    >>>> Are you trying to reinvent ?expand.grid ?
    >>>> 
    >>>> -- Bert
    >>>> 
    >>>> Bert Gunter Genentech Nonclinical Biostatistics (650)
    >>>> 467-7374
    >>>> 
    >>>> "Data is not information. Information is not
    >>>> knowledge. And knowledge is certainly not wisdom."
    >>>> Clifford Stoll
    >>>> 
 [...............]



[Rd] \alias{} --> rather \concept{} for conceptual "links" to help pages
Martin Maechler