assertive ex 1: using assertions

library(assertive)

## assertive has some important changes.  Read ?changes for details.

library(knitr)
opts_chunk$set(error = TRUE)

Before you begin, get to know your way around the assertive package. Take a look at ls("package:assertive") and have a quick read of ?assertive.

Consider the variable, x:

x <- with(expand.grid(x = -1:1, y = -1:0), x / y)

Write a check that x is a numeric vector.

# check for being numeric
assert_is_numeric(x)

Write a check that all the elements of x are finite.

# check for being finite
assert_all_are_finite(x)

## Error in eval(expr, envir, enclos): x are not all finite.
## There were 3 failures:
##   Position Value        Cause
## 1        4  -Inf     infinite
## 2        5   NaN not a number
## 3        6   Inf     infinite

Write a check that all the elements of x are not missing.

# check for having no missing values
assert_all_are_not_na(x)

## Error in eval(expr, envir, enclos): The values of x are sometimes NA.
## There was 1 failure:
##   Position Value   Cause
## 1        5   NaN missing

Consider the variable, y:

y <- seq.int(-pi, 3 * pi, pi)

Write some checks that y contains only numbers greater than or equal to zero, and less than two pi. (Be careful with boundary values.)

# checks for range here
assert_all_are_in_right_open_range(y, 0, 2 * pi)

## Error in eval(expr, envir, enclos): y are not all in the range [0,6.28318530717959).
## There were 3 failures:
##   Position             Value    Cause
## 1        1 -3.14159265358979  too low
## 2        4  6.28318530717959 too high
## 3        5  9.42477796076938 too high

Consider the list variable, z.

z <- list(a = rnbinom(10, 5, 0.5))

Is it a scalar object? Use is_scalar with both metrics to see.

# checks for size here
is_scalar(z) # implicitly metric = "length"

## [1] TRUE

is_scalar(z, metric = "elements")

## [1] FALSE
## Cause of failure:  z has 10 elements, not 1.