[Rd] abline and its documentation

François Pinard pinard at iro.umontreal.ca
Thu May 4 00:04:36 CEST 2006

Hi, people.  The documentation of abline says:


     abline(a, b, untf = FALSE, ...)
     abline(h=, untf = FALSE, ...)
     abline(v=, untf = FALSE, ...)
     abline(coef=, untf = FALSE, ...)
     abline(reg=, untf = FALSE, ...)

so suggesting that h= and v= usages are exclusive.  There are examples 
in the mailing list archives of using both at the same time, and I find 
convenient, for example, doing:

    abline(h=0, v=0, ...)

for bolding the position of the origin or the axes through the origin.

By doing so, we are using undocumented capabilities of abline and 
consequently, writing bugged R code.  It does not matter so much 
interactively, but scripts may be more sensitive.

Would it be acceptable to amend abline documentation, so to commit the 
capability of abline to do both h= and v= at once?   Or even combined 
with intercept and slope?  (abline is able to do all three at once 
already!)  Then, R users and code could more safely rely on this.

Just a suggestion, and not a big matter, of course! :-)

François Pinard   http://pinard.progiciels-bpi.ca

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