I'd like to second Vincent's appeal.
Before 'head' and 'tail' were added to package:utils, I had versions that allowed negative subscripts.
And I found the code rendered by them readable and less subject to mental or typographical errors.
I think all that is needed for the versions in package::utils is:
if (n < 0 ) n <- length(x) + n
or
if (n < 0 ) n <- nrow(x) + n
as the first line of the body of each method except head.function.
Chuck
On Wed, 20 Apr 2005, Vincent Goulet wrote:
Le 20 Avril 2005 16:05, A.J. Rossini a écrit :x[-length(x)] ?
I feel idiot from that one, but hold on to my point. ;-)
Better example, then: how about a compact way to drop, say, the last 3 elements of a vector? I think
tail(x, -3)
would be nicer --- and more readable --- than
x[-((length(x)-2):length(x))]
or
x[0:3 -length(x)]
or some other convoluted way to achieve the same result.
(BTW, dropping the last element of a vector would be 'tail(x, -1)., not 'tail(x, -length(x))' as stated in my original post. The latter would drop all the elements.)
On 4/20/05, Vincent Goulet <[EMAIL PROTECTED]> wrote:Dear R developers,
I'm a former APL programmer. In that language, the "take" (up arrow) and "drop" (down arrow) operators were extensively used to, well, take and drop elements of vectors. Functions head() and tail() are equivalents in R for the "take" operator, but nothing seems to mimic the "drop" operator. I think it would be useful.
For example, is there any simpler way to extract all elements of a vector but the last one than doing
x[1:(length(x) - 1)] ?
An equivalent of "drop" would make this easy.
Now, I think this could be easily implemented with the existing functions by allowing negative arguments to head() and tail(). For example,
head(x, -1)
would drop the first element of a vector and
tail(x, -length(x))
the last one.
Is there any interest for such an extension?
I would be very willing to contribute a patch, although I don't have much experience in doing so.
Best regards,
-- Vincent Goulet, Associate Professor École d'actuariat Université Laval, Québec [EMAIL PROTECTED] http://vgoulet.act.ulaval.ca
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-- Vincent Goulet, Professeur agrégé École d'actuariat Université Laval, Québec [EMAIL PROTECTED] http://vgoulet.act.ulaval.ca
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Charles C. Berry (858) 534-2098 Dept of Family/Preventive Medicine E mailto:[EMAIL PROTECTED] UC San Diego http://biostat.ucsd.edu/~cberry/ La Jolla, San Diego 92093-0717
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