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An R package that provides readable check functions to ensure code integrity.

There are times when it is a good idea to check the state of your variables, to ensure that they have the properties that you think they have. For example, if you have a count variable, you might want to check that it is numeric, that all the values are non-negative, and that all the values are whole numbers.

assertive provides lots of functions (“predicates” and “assertions”) to provide such checks. It is designed to make your code very easy to read, and to provide highly informative error messages.


To install the stable version, type:


To install the development version, you first need the devtools package.


Then you can install the assertive package using


How to use the package

assertive contains lots of assert functions (“assertions”) that throw errors if conditions aren’t met. They are very useful for checking user input to your functions.

For example,

f <- function(x)
  x + 1
## [1] 2
## Error in f(NULL) : x is NULL.

(You can think of the assert functions as more specific versions of base::stopifnot that make your code easier to read and give more informative error messages.)

Each assert function has a corresponding is function (a “predicate”). In this case, is_not_null is a wrapper to base-R’s !is.null, that gives a more informative error message on failure (in an attribute named cause).

## [1] TRUE

## [1] FALSE
## Cause of failure:  NULL is NULL.

Many of the is functions are wrappers to base functions. They all return causes of failure, and they have consistent naming, beginning is_ or has_ (so base::interactive becomes is_interactive, for example.)

Vectorised is functions

Some is functions return a logical vector rather than a single value. In this case the input values are returned in the names to make it easier to see which values succeeded/failed, and the cause attribute is also vectorised.

For example,

is_positive(c(1, 0, -1, NA))
## There were 3 failures:
##   Position Value   Cause
## 1        2     0 too low
## 2        3    -1 too low
## 3        4  <NA> missing

Using unclass, you can see that this is just a logical vector, with a cause attribute.

unclass(is_positive(c(1, 0, -1, NA)))
##     1     0    -1  <NA> 
## attr(,"cause")
## [1]         too low too low missing

There are two corresponding assert functions for these vectorised is functions.

assert_any_are_positive(c(1, 0, -1, NA)) # test passed since 1 is positive
assert_all_are_positive(c(1, 0, -1, NA))
## Error: c(1, 0, -1, NA) contains non-positive values.
## There were 3 failures:
##   Position Value   Cause
## 1        2     0 too low
## 2        3    -1 too low
## 3        4  <NA> missing

Can’t I just use testthat?

testthat is an excellent package for writing unit tests, and I recommend that you use it. Unit tests are a form of development-time testing. That is, you write the tests while you develop your code in order to check that you haven’t made any mistakes.

assertive, and assertions in general, are for run-time testing. That is, you include them in your code to check that the user hasn’t made a mistake while running your code.

The virtual package system

assertive is a virtual package; it does not contain any functions, but merely reexports them from lower-level packages. For a complete reference, see the individual package pages.

assertive.base contains the core functionality. For example, is_true checks when inputs return TRUE. It also contains some utility functions, such as use_first, which returns the first value of a vector, warning you if it was longer than length one. contains checks on properties of variables. For example, is_scalar checks for values that have length one, and has_duplicates checks for the presence of duplicate values.

assertive.types contains checks for types of variables. For example, is_character wraps the base is.character, while is_a_string combines that check with is_scalar to check for single strings.

assertive.numbers contains checks for numbers. For example, is_in_range checks if a number is in a numeric range.

assertive.strings contains checks for strings. For example, is_an_empty_string checks if a character vector contains a single empty string.

assertive.datetimes contains checks for dates and times. For example, is_in_past checks if a Date or POSIXt obejct is in the past.

assertive.files contains checks for files and connections. For example, is_readable_file checks if a path points to a file that R has permission to read, and is_file_connection check if an object is a file connection.

assertive.sets contains checks for sets. For example, is_subset checks if a vector is a subset of another vector.

assertive.matrices contains checks for matrices. For example, is_symmetric_matrix checks if a matrix is symmetric.

assertive.models contains checks for models. For example, is_empty_model checks if a model is the empty model (no factors). contains checks for complex data types. For example, is_credit_card_number checks a character vector for valid credit card numbers. contains checks for UK-specific complex data types. For example, is_uk_postcode checks a character vector for valid UK postcodes. contains checks for US-specific complex data types. For example, is_us_telephone_number checks a character vector for valid US telephone numbers.

assertive.reflection contains checks on the state of R. For example, is_solaris tests for that operating system, and is_rstudio tests for that IDE.

assertive.code contains checks for code. For example, is_valid_variable_name checks whether a character vector contains valid variable names.

I hate this; what’s the alternative?

There are at least five other R packages for doing assertions. In alphabetical order of package:

I want to know more

There are several vignettes with more details on how to use the package, including case studies and exercises. Find them using


I want to help

The assertive packages are in the process of being translated into many languages. If you speak a language other than English, and have an hour or two spare, your translation skills would be appreciated.

assertive is also currently lacking assertions for time series, spatial data, personal data for countries other than the UK and US, and industry-sector-specific data. If you want to contribute a package for these data types, let me know and I can talk you through how to do it.