Why does assert_that say that an assertion must return a logical value, when all(between(...)) does return a single logical value?

Question

I'm writing a very simple piece of R code that, among other things, uses assert_that to check that a value is between 0 and 1. It should throw an error if the variable in the data frame is outside this range.

This simple code throws an error that says Error: assert_that: assertion must return a logical value, but all(between(...)) does return a single logical value of TRUE.

library(assertthat)
library(tidyverse)

data <- tibble(`Var 1` = c(0.1, 0.2, 0.5), `Var 2` = c(0.1, 2, 5))

data %>%
  assert_that(all(between(`Var 1`, 0, 1)))

Why is assert_that failing here? I'm using backticks in the variable name because the actual code file has spaces in the variable names so I'm emulating that in my minimal example.

Answer 1

Pipes pass their input as the first argument of the functional expression on the right-hand side (or at least the first unmatched argument). Your pipe expression is equivalent to evaluating

assert_that(data, all(between(`Var 1`, 0, 1)))

The first thing assert_that is testing for TRUE/FALSE is data, which isn't a logical value ...

I don't know if there's a more rlang-ish way to do this, but

data |> 
    with(expr=all(between(`Var 1`, 0, 1))) |> 
    assert_that()

seems to work.

If it were me I would just skip the pipe:

assert_that(all(between(data[["Var 1"]], 0, 1)))

@zephryl points to this related question, which points out that you should also be able to do this with %$%, the magrittr exposition pipe:

library(magrittr)
data %$% assert_that(all(between(`Var 1`, 0, 1)))  ## TRUE