| sort {base} | R Documentation |
Sort (or order) a numeric or complex vector (partially) into ascending (or descending) order.
sort(x, partial = NULL, na.last = NA, decreasing = FALSE,
method = c("shell", "quick"), index.return = FALSE)
is.unsorted(x, na.rm = FALSE)
x |
a numeric or complex vector. |
partial |
a vector of indices for partial sorting. |
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. |
decreasing |
logical. Should the sort be increasing or decreasing? |
method |
character specifying the algorithm used. |
index.return |
logical indicating if the ordering index vector should
be returned as well; this is only available for the default
na.last = NA. |
na.rm |
logical. Should missing values be removed? |
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.
The sort order for character vectors will depend on the collating
sequence of the locale in use: see Comparison.
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. 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 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.
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.
require(stats)
data(swiss)
x <- swiss$Education[1:25]
x; sort(x); sort(x, partial = c(10, 15))
median # 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 <- 50 # << adjust to your CPU
c1 <- c2 <- numeric(Sim)
for(is in 1:Sim){
x <- rnorm(N)
gc() ## sort should not have to pay for gc
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, meth = "s") == sort(x, meth = "q"))
}
100 * 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(1e6)
gc()
system.time(x1 <- sort(x, method = "shell"))
gc()
system.time(x2 <- sort(x, method = "quick"))
stopifnot(identical(x1, x2))
## End(Not run)