For a package providing 'virtual' data.frames backed by MonetDB database
tables, we want to make some functions generic, to implement versions that
work on single or multiple database columns.

My approach was

sd <- function(x, na.rm=TRUE,...) UseMethod("sd")

sd.default<- base::sd

I've done that before to make dotchart() generic in the 'survey' package.

With dotchart() (and even sd()) there still doesn't seem to be a problem
(based on the CRAN check results), but with var() we get a note

Found .Internal call in the following function:
  ‘var.default’
with calls to .Internal functions
  ‘cov’

because base::var contains calls to .Internal.  These seems harmless to me
-- the package is only calling .Internal() through base functions in usual
way.

We could use
   var.default<-function(x, y=NULL, na.rm=TRUE, ...)
base::var(x,y,na.rm,...)

but it seems that could have different lazy-evaluation behaviour.

    -thomas

-- 
Thomas Lumley
Professor of Biostatistics
University of Auckland

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