model_offset() extracts a numeric offset from a model frame. It is
inspired by stats::model.offset(), but has nicer error messages and
is slightly stricter.
Arguments
- terms
A
"terms"object corresponding todata, returned from a call tomodel_frame().- data
A data frame returned from a call to
model_frame().
Details
If a column that has been tagged as an offset is not numeric, a nice error message is thrown telling you exactly which column was problematic.
stats::model.offset() also allows for a column named "(offset)" to be
considered an offset along with any others that have been tagged by
stats::offset(). However, stats::model.matrix() does not recognize
these columns as offsets (so it doesn't remove them as it should). Because
of this inconsistency, columns named "(offset)" are not treated specially
by model_offset().
Examples
x <- model.frame(Species ~ offset(Sepal.Width), iris)
model_offset(terms(x), x)
#> [1] 3.5 3.0 3.2 3.1 3.6 3.9 3.4 3.4 2.9 3.1 3.7 3.4 3.0 3.0 4.0 4.4 3.9
#> [18] 3.5 3.8 3.8 3.4 3.7 3.6 3.3 3.4 3.0 3.4 3.5 3.4 3.2 3.1 3.4 4.1 4.2
#> [35] 3.1 3.2 3.5 3.6 3.0 3.4 3.5 2.3 3.2 3.5 3.8 3.0 3.8 3.2 3.7 3.3 3.2
#> [52] 3.2 3.1 2.3 2.8 2.8 3.3 2.4 2.9 2.7 2.0 3.0 2.2 2.9 2.9 3.1 3.0 2.7
#> [69] 2.2 2.5 3.2 2.8 2.5 2.8 2.9 3.0 2.8 3.0 2.9 2.6 2.4 2.4 2.7 2.7 3.0
#> [86] 3.4 3.1 2.3 3.0 2.5 2.6 3.0 2.6 2.3 2.7 3.0 2.9 2.9 2.5 2.8 3.3 2.7
#> [103] 3.0 2.9 3.0 3.0 2.5 2.9 2.5 3.6 3.2 2.7 3.0 2.5 2.8 3.2 3.0 3.8 2.6
#> [120] 2.2 3.2 2.8 2.8 2.7 3.3 3.2 2.8 3.0 2.8 3.0 2.8 3.8 2.8 2.8 2.6 3.0
#> [137] 3.4 3.1 3.0 3.1 3.1 3.1 2.7 3.2 3.3 3.0 2.5 3.0 3.4 3.0
xx <- model.frame(Species ~ offset(Sepal.Width) + offset(Sepal.Length), iris)
model_offset(terms(xx), xx)
#> [1] 8.6 7.9 7.9 7.7 8.6 9.3 8.0 8.4 7.3 8.0 9.1 8.2 7.8
#> [14] 7.3 9.8 10.1 9.3 8.6 9.5 8.9 8.8 8.8 8.2 8.4 8.2 8.0
#> [27] 8.4 8.7 8.6 7.9 7.9 8.8 9.3 9.7 8.0 8.2 9.0 8.5 7.4
#> [40] 8.5 8.5 6.8 7.6 8.5 8.9 7.8 8.9 7.8 9.0 8.3 10.2 9.6
#> [53] 10.0 7.8 9.3 8.5 9.6 7.3 9.5 7.9 7.0 8.9 8.2 9.0 8.5
#> [66] 9.8 8.6 8.5 8.4 8.1 9.1 8.9 8.8 8.9 9.3 9.6 9.6 9.7
#> [79] 8.9 8.3 7.9 7.9 8.5 8.7 8.4 9.4 9.8 8.6 8.6 8.0 8.1
#> [92] 9.1 8.4 7.3 8.3 8.7 8.6 9.1 7.6 8.5 9.6 8.5 10.1 9.2
#> [105] 9.5 10.6 7.4 10.2 9.2 10.8 9.7 9.1 9.8 8.2 8.6 9.6 9.5
#> [118] 11.5 10.3 8.2 10.1 8.4 10.5 9.0 10.0 10.4 9.0 9.1 9.2 10.2
#> [131] 10.2 11.7 9.2 9.1 8.7 10.7 9.7 9.5 9.0 10.0 9.8 10.0 8.5
#> [144] 10.0 10.0 9.7 8.8 9.5 9.6 8.9
# Problematic columns are caught with intuitive errors
tryCatch(
expr = {
x <- model.frame(~ offset(Species), iris)
model_offset(terms(x), x)
},
error = function(e) {
print(e$message)
}
)
#> [1] "Column \033[34m\"offset(Species)\"\033[39m is tagged as an offset and thus must be\n numeric, not a \033[34m<factor>\033[39m object."