sort_linter: Check for common mistakes around sorting vectors

In r-lib/lintr: A 'Linter' for R Code

Check for common mistakes around sorting vectors

Description

This linter checks for some common mistakes when using order() or sort().

Usage

sort_linter()

Details

First, it requires usage of sort() over .[order(.)].

sort() is the dedicated option to sort a list or vector. It is more legible and around twice as fast as .[order(.)], with the gap in performance growing with the vector size.

Second, it requires usage of is.unsorted() over equivalents using sort().

The base function is.unsorted() exists to test the sortedness of a vector. Prefer it to inefficient and less-readable equivalents like x != sort(x). The same goes for checking x == sort(x) – use !is.unsorted(x) instead.

Moreover, use of x == sort(x) can be risky because sort() drops missing elements by default, meaning == might end up trying to compare vectors of differing lengths.

Tags

best_practices, efficiency, readability

See Also

linters for a complete list of linters available in lintr.

Examples

# will produce lints
lint(
  text = "x[order(x)]",
  linters = sort_linter()
)

lint(
  text = "x[order(x, decreasing = TRUE)]",
  linters = sort_linter()
)

lint(
  text = "sort(x) == x",
  linters = sort_linter()
)

# okay
lint(
  text = "x[sample(order(x))]",
  linters = sort_linter()
)

lint(
  text = "y[order(x)]",
  linters = sort_linter()
)

lint(
  text = "sort(x, decreasing = TRUE) == x",
  linters = sort_linter()
)

# If you are sorting several objects based on the order of one of them, such
# as:
x <- sample(1:26)
y <- letters
newx <- x[order(x)]
newy <- y[order(x)]
# This will be flagged by the linter. However, in this very specific case,
# it would be clearer and more efficient to run order() once and assign it
# to an object, rather than mix and match order() and sort()
index <- order(x)
newx <- x[index]
newy <- y[index]

r-lib/lintr documentation built on Dec. 20, 2024, 7:24 p.m.