sort {base}R Documentation

Sorting or Ordering Vectors


Sort (or order) a vector or factor (partially) into ascending (or descending) order. For ordering along more than one variable, e.g., for sorting data frames, see order.


sort(x, decreasing = FALSE, ...)

## Default S3 method:
sort(x, decreasing = FALSE, na.last = NA, ...), partial = NULL, na.last = NA, decreasing = FALSE,
         method = c("shell", "quick"), index.return = FALSE)

is.unsorted(x, na.rm = FALSE)


x for sort, an R object with a class or a numeric, complex, character or logical vector. For, a numeric, complex, character or logical vector, or a factor.
decreasing logical. Should the sort be increasing or decreasing? Not available for partial sorting.
... arguments to be passed to or from methods or (for the default methods and objects without a class) to
na.last for controlling the treatment of NAs. If TRUE, missing values in the data are put last; if FALSE, they are put first; if NA, they are removed.
partial NULL or an integer vector of indices for partial sorting.
method character string specifying the algorithm used.
index.return logical indicating if the ordering index vector should be returned as well; this is only available for a few cases, the default na.last = NA and full sorting of non-factors.
na.rm logical. Should missing values be removed?


sort is a generic function for which methods can be written, and is the internal method which is compatible with S if only the first three arguments are used.

If partial is not NULL, it is taken to contain indices of elements of x which are to be placed in their correct positions by partial sorting. After the sort, the values specified in partial are in their correct position in the sorted array. Any values smaller than these values are guaranteed to have a smaller index in the sorted array and any values which are greater are guaranteed to have a bigger index in the sorted array. (This is included for efficiency, and many of the options are not available for partial sorting. It is only substantially more efficient if partial has a handful of elements, and a full sort is done if there are more than 10.) Names are discarded for partial sorting.

Complex values are sorted first by the real part, then the imaginary part.

The sort order for character vectors will depend on the collating sequence of the locale in use: see Comparison. The sort order for factors is the order of their levels (which is particularly appropriate for ordered factors).

is.unsorted returns a logical indicating if x is sorted increasingly, i.e., is.unsorted(x) is true if any(x != sort(x)) (and there are no NAs).

Method "shell" uses Shellsort (an O(n^{4/3}) variant from Sedgewick (1996)). If x has names a stable sort is used, so ties are not reordered. (This only matters if names are present.)

Method "quick" uses Singleton's Quicksort implementation and is only available when x is numeric (double or integer) and partial is NULL. (For other types of x Shellsort is used, silently.) It is normally somewhat faster than Shellsort (perhaps twice as fast on vectors of length a million) but has poor performance in the rare worst case. (Peto's modification using a pseudo-random midpoint is used to make the worst case rarer.) This is not a stable sort, and ties may be reordered.


For sort, the result depends on the S3 method which is dispatched. If x does not have a class the rest of this section applies. For classed objects which do not have a specific method the default method will be used and is equivalent to x[order(x, ...)]: this depends on the class having a suitable method for [ (and also that order will work, which is not the case for a class based on a list).
For the sorted vector unless index.return is true, when the result is a list with components named x and ix containing the sorted numbers and the ordering index vector. In the latter case, if method == "quick" ties may be reversed in the ordering, unlike sort.list, as quicksort is not stable.
All attributes are removed from the return value (see Becker et al, 1988, p.146) except names, which are sorted. (If partial is specified even the names are removed.) Note that this means that the returned value has no class, except for factors and ordered factors (which are treated specially and whose result is transformed back to the original class).


Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.

Sedgewick, R. (1986) A new upper bound for Shell sort. J. Algorithms 7, 159–173.

Singleton, R. C. (1969) An efficient algorithm for sorting with minimal storage: Algorithm 347. Communications of the ACM 12, 185–187.

See Also

order for sorting on or reordering multiple variables.



x <- swiss$Education[1:25]
x; sort(x); sort(x, partial = c(10, 15))
stats:::median.default # shows you another example for 'partial'

## illustrate 'stable' sorting (of ties):
sort(c(10:3,2:12), method = "sh", index=TRUE) # is stable
## $x : 2  3  3  4  4  5  5  6  6  7  7  8  8  9  9 10 10 11 12
## $ix: 9  8 10  7 11  6 12  5 13  4 14  3 15  2 16  1 17 18 19
sort(c(10:3,2:12), method = "qu", index=TRUE) # is not
## $x : 2  3  3  4  4  5  5  6  6  7  7  8  8  9  9 10 10 11 12
## $ix: 9 10  8  7 11  6 12  5 13  4 14  3 15 16  2 17  1 18 19
##        ^^^^^

## Not run: ## Small speed comparison simulation:
N <- 2000
Sim <- 20
rep <- 1000 # << adjust to your CPU
c1 <- c2 <- numeric(Sim)
for(is in 1:Sim){
  x <- rnorm(N)
  c1[is] <- system.time(for(i in 1:rep) sort(x, method = "shell"))[1]
  c2[is] <- system.time(for(i in 1:rep) sort(x, method = "quick"))[1]
  stopifnot(sort(x, method = "s") == sort(x, method = "q"))
rbind(ShellSort = c1, QuickSort = c2)
cat("Speedup factor of quick sort():\n")
summary({qq <- c1 / c2; qq[is.finite(qq)]})

## A larger test
x <- rnorm(1e7)
system.time(x1 <- sort(x, method = "shell"))
system.time(x2 <- sort(x, method = "quick"))
stopifnot(identical(x1, x2))
## End(Not run)

[Package base version 2.5.0 Index]