I know that it has been discussed in the past, but I wanted to ask
to revisit the idea of exporting
is.formula <- function(x) inherits(x, "formula")
from 'stats', parallel to is.data.frame() in 'base', given how
widely formulae are used these days in conjunction with data frames,
even outside of model fitting functions (e.g., for split-apply).
One could argue that today data frames and formulae go hand in hand,
and that the lack of is.formula() is a rather ugly asymmetry ...
Furthermore, 'formula' is one of the only S3 classes generated by way
of a primitive (the `~` operator, calling do_tilde() in names.c), so
it is really in some sense "special" { compared to 'factor',
'POSIXlt',
etc. }.
What do people think?
In case it helps, I've gathered some data from 'base' and the
so-called
'defaultPackages', reproduced by the attached R script ... see below.
Mikael
----------------------------
1. For which X does is.X() have no corresponding as.X()?
[1] "R" "atomic" "element"
"finite" "hashtab" "infinite"
[7] "language" "leaf" "loaded"
"mts" "na" "nan"
[13] "object" "primitive" "recursive"
"tskernel" "unsorted"
2. For which Y does as.Y() have no corresponding is.Y()?
[1] "Date" "POSIXct" "POSIXlt"
"dendrogram"
[5] "difftime" "dist" "formula"
"graphicsAnnot"
[9] "hclust" "hexmode" "octmode"
"person"
[13] "personList" "roman"
3. For which Z does is.Z() just call inherits(., "Z")?
[1] "data.frame" "factor"
"numeric_version" "ordered"
[5] "package_version" "raster"
"relistable" "table"
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