Introduction
Objects in R are converted (‘coerced’) to a common type when combined
in a vector, see help("c"). The type of the vector, and
thus of all its components, will be the highest type of the components
in the hierarchy NULL < raw <
logical < integer < double
< complex < character <
list < expression, see the section
‘Details’ in help("c") and the section ‘Value’ in
help("typeof"). For example, numeric 314 will
be coerced to character "314" when it is combined in a
vector with character "nco", such that
c(314, "nco") results in the character vector
c("314", "nco"). This also holds for the logical
NA, which will be coerced to NA_character_
that is printed as NA, as is the logical
NA.
Consequences for checks
As a consequence of type coercion, code like
all_characters(c(x, y)) does not check if
all elements in x and y have type
character: x and y will be
coerced to the highest of their types before the check is performed,
such that all_characters(c(x, y)) checks if any of
x or y has type character
and none of x or y has a
higher type.
To check if all elements in x and y have
type character, use
all_characters(x) && all_characters(y) or, to
generalise more easily to more than two objects,
all(unlist(lapply(X = list(x, y), FUN = all_characters))).
Other function arguments passed to all_characters(), e.g.,
allow_empty = TRUE to allow empty quotes (""),
should be placed behind argument FUN.
Elements of a list can have different types. Using
unlist() on a list creates a vector, coercing all elements
of the list to the highest of their types, such that
all_characters(unlist(z)) does not check
if all elements of list z have type character
but if any element of z has type character
and none of the elements of z has a higher
type.
library(checkinput)
x <- 1:3
all_characters(x)
#> [1] FALSE
y <- letters[x]
all_characters(y)
#> [1] TRUE
all_characters(c(x, y)) # TRUE, even though 'x' is numeric!
#> [1] TRUE
all_characters(x) && all_characters(y)
#> [1] FALSE
all(unlist(lapply(X = list(x, y), FUN = all_characters)))
#> [1] FALSE
z <- list("a", 2, "c")
z
#> [[1]]
#> [1] "a"
#>
#> [[2]]
#> [1] 2
#>
#> [[3]]
#> [1] "c"
lapply(X = z, class)
#> [[1]]
#> [1] "character"
#>
#> [[2]]
#> [1] "numeric"
#>
#> [[3]]
#> [1] "character"
# TRUE, even though the second element of 'z' is numeric!
all_characters(unlist(z))
#> [1] TRUE
all(unlist(lapply(X = z, FUN = all_characters)))
#> [1] FALSEZero-length values
Although zero-length objects (see help("is_zerolength"))
are discarded when combined into a vector with other values, their types
are taken into account for type coercion. For example, the number
314 has type double but will be coerced to
character-type "314" when combined into a vector with
zero-length character(0), such that
c(314, character(0)) results in the character string
"314", not in the number
314.
class, type, and mode
There are several ways to define the ‘type’ (in the loose sense of
the word) of R objects. The following table gives an overview of the
type (typeof()), mode (mode()) and class
(class()) of various objects. The overview shows
differences between floating-point numbers such as 3.2 and
integers such as 3L: they both have mode
numeric but different types and classes. Factors have type
factor, mode numeric and class
integer.
#> class mode type
#> NULL "NULL" "NULL" "NULL"
#> TRUE "logical" "logical" "logical"
#> 1L "integer" "numeric" "integer"
#> 1.2 "numeric" "numeric" "double"
#> complex "complex" "complex" "complex"
#> character "character" "character" "character"
#> list "list" "list" "list"
#> factor "factor" "numeric" "integer"is.numeric() checks the mode of
x, see the ‘Note on names’ in
help("is.numeric"), but returns FALSE for
factors. To test the class of x, use
inherits(x = x, what = "numeric") or
"numeric" %in% class(x), not
class(x) == "numeric" that will fail with an error if
x has multiple classes.
sessionInfo
#> R version 4.6.1 (2026-06-24)
#> Platform: x86_64-pc-linux-gnu
#> Running under: Ubuntu 24.04.5 LTS
#>
#> Matrix products: default
#> BLAS: /usr/lib/x86_64-linux-gnu/openblas-pthread/libblas.so.3
#> LAPACK: /usr/lib/x86_64-linux-gnu/openblas-pthread/libopenblasp-r0.3.26.so; LAPACK version 3.12.0
#>
#> locale:
#> [1] LC_CTYPE=C.UTF-8 LC_NUMERIC=C LC_TIME=C.UTF-8
#> [4] LC_COLLATE=C.UTF-8 LC_MONETARY=C.UTF-8 LC_MESSAGES=C.UTF-8
#> [7] LC_PAPER=C.UTF-8 LC_NAME=C LC_ADDRESS=C
#> [10] LC_TELEPHONE=C LC_MEASUREMENT=C.UTF-8 LC_IDENTIFICATION=C
#>
#> time zone: UTC
#> tzcode source: system (glibc)
#>
#> attached base packages:
#> [1] stats graphics grDevices utils datasets methods base
#>
#> other attached packages:
#> [1] checkinput_1.5.2
#>
#> loaded via a namespace (and not attached):
#> [1] digest_0.6.39 desc_1.4.3 R6_2.6.1 fastmap_1.2.0
#> [5] xfun_0.62 cachem_1.1.0 knitr_1.52 htmltools_0.5.9
#> [9] rmarkdown_2.32 lifecycle_1.0.5 cli_3.6.6 sass_0.4.10
#> [13] pkgdown_2.2.1 textshaping_1.0.5 jquerylib_0.1.4 systemfonts_1.3.2
#> [17] compiler_4.6.1 tools_4.6.1 ragg_1.5.2 bslib_0.12.0
#> [21] evaluate_1.0.5 yaml_2.3.12 otel_0.2.0 jsonlite_2.0.0
#> [25] rlang_1.3.0 fs_2.1.0