Ever used an R function that produced a not-very-helpful error message, just to discover after minutes of debugging that you simply passed a wrong argument?
Blaming the laziness of the package author for not doing such standard checks (in a dynamically typed language such as R) is at least partially unfair, as R makes these types of checks cumbersome and annoying. Well, that’s how it was in the past.
Enter checkmate.
Virtually every standard type of user error when passing arguments into function can be caught with a simple, readable line which produces an informative error message in case. A substantial part of the package was written in C to minimize any worries about execution time overhead.
As a motivational example, consider you have a function to calculate
the faculty of a natural number and the user may choose between using
either the stirling approximation or R’s factorial
function
(which internally uses the gamma function). Thus, you have two
arguments, n
and method
. Argument
n
must obviously be a positive natural number and
method
must be either "stirling"
or
"factorial"
. Here is a version of all the hoops you need to
jump through to ensure that these simple requirements are met:
fact <- function(n, method = "stirling") {
if (length(n) != 1)
stop("Argument 'n' must have length 1")
if (!is.numeric(n))
stop("Argument 'n' must be numeric")
if (is.na(n))
stop("Argument 'n' may not be NA")
if (is.double(n)) {
if (is.nan(n))
stop("Argument 'n' may not be NaN")
if (is.infinite(n))
stop("Argument 'n' must be finite")
if (abs(n - round(n, 0)) > sqrt(.Machine$double.eps))
stop("Argument 'n' must be an integerish value")
n <- as.integer(n)
}
if (n < 0)
stop("Argument 'n' must be >= 0")
if (length(method) != 1)
stop("Argument 'method' must have length 1")
if (!is.character(method) || !method %in% c("stirling", "factorial"))
stop("Argument 'method' must be either 'stirling' or 'factorial'")
if (method == "factorial")
factorial(n)
else
sqrt(2 * pi * n) * (n / exp(1))^n
}
And for comparison, here is the same function using checkmate:
The functions can be split into four functional groups, indicated by their prefix.
If prefixed with assert
, an error is thrown if the
corresponding check fails. Otherwise, the checked object is returned
invisibly. There are many different coding styles out there in the wild,
but most R programmers stick to either camelBack
or
underscore_case
. Therefore, checkmate
offers
all functions in both flavors: assert_count
is just an
alias for assertCount
but allows you to retain your
favorite style.
The family of functions prefixed with test
always return
the check result as logical value. Again, you can use
test_count
and testCount
interchangeably.
Functions starting with check
return the error message
as a string (or TRUE
otherwise) and can be used if you need
more control and, e.g., want to grep on the returned error message.
expect
is the last family of functions and is intended
to be used with the testthat package.
All performed checks are logged into the testthat
reporter.
Because testthat
uses the underscore_case
, the
extension functions only come in the underscore style.
All functions are categorized into objects to check on the package help page.
You can use assert to perform multiple checks at once and throw an assertion if all checks fail.
Here is an example where we check that x is either of class
foo
or class bar
:
Note that assert(, combine = "or")
and
assert(, combine = "and")
allow to control the logical
combination of the specified checks, and that the former is the
default.
The following functions allow a special syntax to define argument
checks using a special format specification. E.g.,
qassert(x, "I+")
asserts that x
is an integer
vector with at least one element and no missing values. This very simple
domain specific language covers a large variety of frequent argument
checks with only a few keystrokes. You choose what you like best.
To extend testthat, you
need to IMPORT, DEPEND or SUGGEST on the checkmate
package.
Here is a minimal example:
# file: tests/test-all.R
library(testthat)
library(checkmate) # for testthat extensions
test_check("mypkg")
Now you are all set and can use more than 30 new expectations in your tests.
In comparison with tediously writing the checks yourself in R (c.f.
factorial example at the beginning of the vignette), R is sometimes a
tad faster while performing checks on scalars. This seems odd at first,
because checkmate is mostly written in C and should be comparably fast.
Yet many of the functions in the base
package are not
regular functions, but primitives. While primitives jump directly into
the C code, checkmate has to use the considerably slower
.Call
interface. As a result, it is possible to write (very
simple) checks using only the base functions which, under some
circumstances, slightly outperform checkmate. However, if you go one
step further and wrap the custom check into a function to convenient
re-use it, the performance gain is often lost (see benchmark 1).
For larger objects the tide has turned because checkmate avoids many
unnecessary intermediate variables. Also note that the quick/lazy
implementation in
qassert
/qtest
/qexpect
is often a
tad faster because only two arguments have to be evaluated (the object
and the rule) to determine the set of checks to perform.
Below you find some (probably unrepresentative) benchmark. But also
note that this one here has been executed from inside knitr
which is often the cause for outliers in the measured execution time.
Better run the benchmark yourself to get unbiased results.
x
is a flaglibrary(checkmate)
library(ggplot2)
library(microbenchmark)
x = TRUE
r = function(x, na.ok = FALSE) { stopifnot(is.logical(x), length(x) == 1, na.ok || !is.na(x)) }
cm = function(x) assertFlag(x)
cmq = function(x) qassert(x, "B1")
mb = microbenchmark(r(x), cm(x), cmq(x))
print(mb)
## Unit: microseconds
## expr min lq mean median uq max neval
## r(x) 3.196 3.4065 24.28395 3.4915 3.6365 2047.999 100
## cm(x) 2.244 2.4295 9.84618 2.4900 2.6300 654.881 100
## cmq(x) 1.583 1.7230 11.26243 1.7735 1.8735 886.414 100
x
is a numeric of length 1000
with no missing nor NaN valuesx = runif(1000)
r = function(x) stopifnot(is.numeric(x), length(x) == 1000, all(!is.na(x) & x >= 0 & x <= 1))
cm = function(x) assertNumeric(x, len = 1000, any.missing = FALSE, lower = 0, upper = 1)
cmq = function(x) qassert(x, "N1000[0,1]")
mb = microbenchmark(r(x), cm(x), cmq(x))
print(mb)
## Unit: microseconds
## expr min lq mean median uq max neval
## r(x) 12.053 12.5885 41.25127 12.8340 13.2595 2815.851 100
## cm(x) 5.270 5.4750 13.73636 5.5955 5.8155 733.418 100
## cmq(x) 6.221 6.3620 15.02894 6.4720 6.5820 835.027 100
x
is a character vector with
no missing values nor empty stringsx = sample(letters, 10000, replace = TRUE)
r = function(x) stopifnot(is.character(x), !any(is.na(x)), all(nchar(x) > 0))
cm = function(x) assertCharacter(x, any.missing = FALSE, min.chars = 1)
cmq = function(x) qassert(x, "S+[1,]")
mb = microbenchmark(r(x), cm(x), cmq(x))
print(mb)
## Unit: microseconds
## expr min lq mean median uq max neval
## r(x) 271.887 275.2180 325.7145 317.9630 319.5055 2409.654 100
## cm(x) 106.999 107.3705 117.2551 108.2525 109.1635 812.224 100
## cmq(x) 119.022 119.2070 128.8608 119.5940 120.1640 995.757 100
x
is a data frame with no
missing valuesN = 10000
x = data.frame(a = runif(N), b = sample(letters[1:5], N, replace = TRUE), c = sample(c(FALSE, TRUE), N, replace = TRUE))
r = function(x) is.data.frame(x) && !any(sapply(x, function(x) any(is.na(x))))
cm = function(x) testDataFrame(x, any.missing = FALSE)
cmq = function(x) qtest(x, "D")
mb = microbenchmark(r(x), cm(x), cmq(x))
print(mb)
## Unit: microseconds
## expr min lq mean median uq max neval
## r(x) 64.480 65.8780 92.15959 66.3690 67.0250 2544.776 100
## cm(x) 34.995 35.4315 47.13145 36.2525 37.0195 955.221 100
## cmq(x) 28.783 28.9630 36.11382 29.3350 29.4800 665.841 100
# checkmate tries to stop as early as possible
x$a[1] = NA
mb = microbenchmark(r(x), cm(x), cmq(x))
print(mb)
## Unit: microseconds
## expr min lq mean median uq max neval
## r(x) 55.133 56.0845 58.00854 56.776 57.7630 104.815 100
## cm(x) 4.869 5.2200 6.19251 6.096 6.5320 25.668 100
## cmq(x) 1.032 1.1820 1.57512 1.563 1.8385 5.520 100
x
is an increasing sequence of
integers with no missing valuesN = 10000
x.altrep = seq_len(N) # this is an ALTREP in R version >= 3.5.0
x.sexp = c(x.altrep) # this is a regular SEXP OTOH
r = function(x) stopifnot(is.integer(x), !any(is.na(x)), !is.unsorted(x))
cm = function(x) assertInteger(x, any.missing = FALSE, sorted = TRUE)
mb = microbenchmark(r(x.sexp), cm(x.sexp), r(x.altrep), cm(x.altrep))
print(mb)
## Unit: microseconds
## expr min lq mean median uq max neval
## r(x.sexp) 29.425 29.661 30.31619 29.8555 30.2820 45.996 100
## cm(x.sexp) 12.783 13.069 22.81053 13.2450 13.6505 874.622 100
## r(x.altrep) 38.392 38.792 58.60127 38.9720 39.2280 1961.558 100
## cm(x.altrep) 3.426 3.807 4.03740 3.9230 4.2230 5.850 100
To extend checkmate a custom check*
function has to be
written. For example, to check for a square matrix one can re-use parts
of checkmate and extend the check with additional functionality:
checkSquareMatrix = function(x, mode = NULL) {
# check functions must return TRUE on success
# and a custom error message otherwise
res = checkMatrix(x, mode = mode)
if (!isTRUE(res))
return(res)
if (nrow(x) != ncol(x))
return("Must be square")
return(TRUE)
}
# a quick test:
X = matrix(1:9, nrow = 3)
checkSquareMatrix(X)
## [1] TRUE
## [1] "Must store characters"
## [1] "Must be square"
The respective counterparts to the check
-function can be
created using the constructors makeAssertionFunction,
makeTestFunction
and makeExpectationFunction:
# For assertions:
assert_square_matrix = assertSquareMatrix = makeAssertionFunction(checkSquareMatrix)
print(assertSquareMatrix)
## function (x, mode = NULL, .var.name = checkmate::vname(x), add = NULL)
## {
## if (missing(x))
## stop(sprintf("argument \"%s\" is missing, with no default",
## .var.name))
## res = checkSquareMatrix(x, mode)
## checkmate::makeAssertion(x, res, .var.name, add)
## }
# For tests:
test_square_matrix = testSquareMatrix = makeTestFunction(checkSquareMatrix)
print(testSquareMatrix)
## function (x, mode = NULL)
## {
## isTRUE(checkSquareMatrix(x, mode))
## }
# For expectations:
expect_square_matrix = makeExpectationFunction(checkSquareMatrix)
print(expect_square_matrix)
## function (x, mode = NULL, info = NULL, label = vname(x))
## {
## if (missing(x))
## stop(sprintf("Argument '%s' is missing", label))
## res = checkSquareMatrix(x, mode)
## makeExpectation(x, res, info, label)
## }
Note that all the additional arguments .var.name
,
add
, info
and label
are
automatically joined with the function arguments of your custom check
function. Also note that if you define these functions inside an R
package, the constructors are called at build-time (thus, there is no
negative impact on the runtime).
The package registers two functions which can be used in other packages’ C/C++ code for argument checks.
These are the counterparts to qassert and qtest. Due to their simplistic interface, they perfectly suit the requirements of most type checks in C/C++.
For detailed background information on the register mechanism, see the Exporting C Code section in Hadley’s Book “R Packages” or WRE. Here is a step-by-step guide to get you started:
checkmate
to your “Imports” and “LinkingTo”
sections in your DESCRIPTION file."checkmate_stub.c"
, see
below.<checkmate.h>
in
each compilation unit where you want to use checkmate.File contents for (2):
For the sake of completeness, here the sessionInfo()
for
the benchmark (but remember the note before on knitr
possibly biasing the results).
## R version 4.4.2 (2024-10-31)
## Platform: x86_64-pc-linux-gnu
## Running under: Ubuntu 24.04.1 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=en_US.UTF-8 LC_NUMERIC=C
## [3] LC_TIME=en_US.UTF-8 LC_COLLATE=C
## [5] LC_MONETARY=en_US.UTF-8 LC_MESSAGES=en_US.UTF-8
## [7] LC_PAPER=en_US.UTF-8 LC_NAME=C
## [9] LC_ADDRESS=C LC_TELEPHONE=C
## [11] LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C
##
## time zone: Etc/UTC
## tzcode source: system (glibc)
##
## attached base packages:
## [1] stats graphics grDevices utils datasets methods base
##
## other attached packages:
## [1] microbenchmark_1.5.0 ggplot2_3.5.1 checkmate_2.3.2
## [4] rmarkdown_2.29
##
## loaded via a namespace (and not attached):
## [1] vctrs_0.6.5 cli_3.6.3 knitr_1.49 rlang_1.1.5
## [5] xfun_0.50 jsonlite_1.8.9 glue_1.8.0 colorspace_2.1-1
## [9] buildtools_1.0.0 backports_1.5.0 htmltools_0.5.8.1 maketools_1.3.1
## [13] sys_3.4.3 sass_0.4.9 scales_1.3.0 grid_4.4.2
## [17] tibble_3.2.1 munsell_0.5.1 evaluate_1.0.3 jquerylib_0.1.4
## [21] fastmap_1.2.0 yaml_2.3.10 lifecycle_1.0.4 compiler_4.4.2
## [25] pkgconfig_2.0.3 farver_2.1.2 digest_0.6.37 R6_2.5.1
## [29] pillar_1.10.1 magrittr_2.0.3 bslib_0.8.0 withr_3.0.2
## [33] tools_4.4.2 gtable_0.3.6 cachem_1.1.0