seq-predicates {scrutiny}

Is a vector a certain kind of sequence?

Description

Predicate functions that test whether x is a numeric vector (or coercible to numeric) with some special properties:

• is_seq_linear() tests whether every two consecutive elements of x differ by some constant amount.

• is_seq_ascending() and is_seq_descending() test whether the difference between every two consecutive values is positive or negative, respectively. is_seq_dispersed() tests whether x values are grouped around a specific central value, from, with the same distance to both sides per value pair. By default (test_linear = TRUE), these functions also test for linearity, like is_seq_linear().

NA elements of x are handled in a nuanced way. See Value section below and the examples in vignette("devtools"), section NA handling.

Usage

is_seq_linear(x, tolerance = .Machine$double.eps^0.5)

is_seq_ascending(x, test_linear = TRUE, tolerance = .Machine$double.eps^0.5)

is_seq_descending(x, test_linear = TRUE, tolerance = .Machine$double.eps^0.5)

is_seq_dispersed(
  x,
  from,
  test_linear = TRUE,
  tolerance = .Machine$double.eps^0.5
)

Arguments

x

Numeric or coercible to numeric, as determined by is_numeric_like(). Vector to be tested.

tolerance

Numeric. Tolerance of comparison between numbers when testing. Default is circa 0.000000015 (1.490116e-08), as in dplyr::near().

test_linear

Logical. In functions other than is_seq_linear(), should x also be tested for linearity? Default is TRUE.

from

Numeric or coercible to numeric. Only in is_seq_dispersed(). It will test whether from is at the center of x, and if every pair of other values is equidistant to it.

Value

A single logical value. If x contains at least one NA element, the functions return either NA or FALSE:

• If all elements of x are NA, the functions return NA.

• If some but not all elements are NA, they check if x might be a sequence of the kind in question: Is it a linear (and / or ascending, etc.) sequence after the NAs were replaced by appropriate values? If so, they return NA; otherwise, they return FALSE.

See Also

validate::is_linear_sequence(), which is much like is_seq_linear() but more permissive with NA values. It comes with some additional features, such as support for date-times.

Examples

# These are linear sequences...
is_seq_linear(x = 3:7)
is_seq_linear(x = c(3:7, 8))

# ...but these aren't:
is_seq_linear(x = c(3:7, 9))
is_seq_linear(x = c(10, 3:7))

# All other `is_seq_*()` functions
# also test for linearity by default:
is_seq_ascending(x = c(2, 7, 9))
is_seq_ascending(x = c(2, 7, 9), test_linear = FALSE)

is_seq_descending(x = c(9, 7, 2))
is_seq_descending(x = c(9, 7, 2), test_linear = FALSE)

is_seq_dispersed(x = c(2, 3, 5, 7, 8), from = 5)
is_seq_dispersed(x = c(2, 3, 5, 7, 8), from = 5, test_linear = FALSE)

# These fail their respective
# individual test even
# without linearity testing:
is_seq_ascending(x = c(1, 7, 4), test_linear = FALSE)
is_seq_descending(x = c(9, 15, 3), test_linear = FALSE)
is_seq_dispersed(1:10, from = 5, test_linear = FALSE)