# Mining R 4.0.0 Changelog for Nuggets of Gold: #1 stopifnot()

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R 4.0.0 has been out for a while, now, and — apart from a case where `merge()`

was slower than dirt — it’s been really stable for at least me (I use it daily on macOS, Linux, and Windows). Sure, it came with some headline-grabbing features/upgrades, but I’ve started looking at what other useful nuggets might be in the changelog and decided to blog them as I find them.

Today’s nugget is the venerable `stopifnot()`

function which was significantly enhanced by this PR by Neil Fultz.

Prior to R 4.0.0, if you wanted to use `stopifnot()`

to perform some input validation (a.k.a. — in this case — [assertions])(https://en.wikipedia.org/wiki/Assertion_(software_development)) you’d do something like this (I’m borrowing from Neil’s example):

some_ƒ <- function(alpha, gradtol, steptol, interlim) { stopifnot( (is.numeric(alpha)), (length(alpha) == 1), (alpha > 0), (alpha < 1), (is.numeric(gradtol)), (length(gradtol) == 1), (gradtol > 0), (is.numeric(steptol)), (length(steptol) == 1), (steptol > 0), (is.numeric(interlim)), (length(interlim) == 1), (interlim > 0) ) message("Do something awesome") }

When run with acceptable inputs we get:

some_ƒ(0.5, 3, 10, 100) ## Do something awesome

But, when run with something out of kilter:

some_ƒ("a", 3, 10, 100) ## Error in some_ƒ("a", 3, 10, 100) : (is.numeric(alpha)) is not TRUE

we get a semi-useful, but somewhat unfriendly message back. Sure, it points to the right expression, but we’re supposed to be the kinder, friendlier data science (and general purpose) language who cares a bit more about our users. To that end, many folks switch to doing something like this:

some_ƒ <- function(alpha, gradtol, steptol, interlim) { if (!is.numeric(alpha)) { stop('Error: alpha should be numeric') } if (length(alpha) != 1) { stop('Error: alpha should be a single value'); } if (alpha < 0) { stop('Error: alpha is negative'); } if (alpha > 1) { stop('Error: alpha is greater than one'); } if (!is.numeric(gradtol)) { stop('Error: gradtol should be numeric') } if (length(gradtol) != 1) { stop('Error: gradtol should be a single value'); } if (gradtol <= 0) { stop('Error: gradtol should be positive'); } if (!is.numeric(steptol)) { stop('Error: steptol should be numeric') } if (length(steptol) != 1) { stop('Error: steptol should be a single value'); } if (steptol <= 0) { stop('Error: steptol should be positive'); } if (!is.numeric(iterlim)) { stop('Error: iterlim should be numeric') } if (length(iterlim) != 1) { stop('Error: iterlim should be a single value'); } if (iterlim <= 0) { stop('Error: iterlim should be positive'); } message("Do something awesome") }

which results in:

some_ƒ("a", 3, 10, 100) ## Error in some_ƒ("a", 3, 10, 100) : Error: alpha should be numeric

(you can make even better error messages than that).

Neal thought there had to be a better way, and made one! The `...`

expressions can be *named* and those names will become the error message:

some_ƒ <- function(alpha, gradtol, steptol, interlim) { stopifnot( 'alpha should be numeric' = (is.numeric(alpha)), 'alpha should be a single value' = (length(alpha) == 1), 'alpha is negative' = (alpha > 0), 'alpha is greater than one' = (alpha < 1), 'gradtol should be numeric' = (is.numeric(gradtol)), 'gradtol should be a single value' = (length(gradtol) == 1), 'gradtol should be positive' = (gradtol > 0), 'steptol should be numeric' = (is.numeric(steptol)), 'steptol should be a single value' = (length(steptol) == 1), 'steptol should be positive' = (steptol > 0), 'iterlim should be numeric' = (is.numeric(interlim)), 'iterlim should be a single value' = (length(interlim) == 1), 'iterlim should be positive' = (interlim > 0) ) message("Do something awesome") } some_ƒ("a", 3, 10, 100) ## Error in some_ƒ("a", 3, 10, 100) : alpha should be numeric

Way easier to write and way more respectful to the caller.

### Gratuitous Statistics

CRAN has ~2,600 packages that use `stopifnot()`

in their package `/R/`

code with the following selected distributions (charts are all log10 scale):

Here are the packages with 50 or more files using `stopifnot()`

:

pkg n1 spatstat 252 2 pracma 145 3 QuACN 80 4 raster 74 5 spdep 61 6 lavaan 54 7 surveillance 53 8 copula 50

Here are the packages with one or more files that have 100 or more calls to `stopifnot()`

in them:

pkg fil ct1 ff ordermerge.R 278 2 OneArmPhaseTwoStudy zzz.R 142 3 bit64 integer64.R 137 4 updog rflexdog.R 124 5 RNetCDF RNetCDF.R 123 6 Rlda rlda.R 105 7 aster2 transform.R 105 8 ads fads.R 104 9 georob georob_exported_functions.R 104 10 bit64 highlevel64.R 101

O_O That’s quite a bit of checking!

### FIN

If you’re working on switching to R 4.0.0 or have switched, this and many other new features await! Drop a note in the comments with your favorite new feature (or, even better, a link to a blog post on said feature!).

As I get time to dig out some more nuggets I’ll add more posts to this series.

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**R – rud.is**.

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