sort {base} | R Documentation

## Sorting or Ordering Vectors

### Description

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`.

### Usage

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

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

### Arguments

`x` | a numeric, complex, character or logical vector, or a factor.
`partial` | a vector of indices for partial sorting.
`na.last` | for controlling the treatment of `NA`s. 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? Not available for partial sorting.
`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 a few cases, the default `na.last = NA` and full sorting of non-factors.
`na.rm` | logical. Should missing values be removed?

### Details

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 as from R 2.3.0 a full sort is done if there are more than 10.) Names are discarded for partial sorting.

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 `NA`s).

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.

### Value

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.
As from R 2.3.0, all attributes are removed from the return value except names, which are sorted. (If `partial` is specified even the names are removed.)

### References

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.

`rank`.

### Examples

    require(stats)
    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)
      c1[is] <- system.time(for(i in 1:rep) sort(x, method = "shell"),
                            gcFirst = TRUE)[1]
      c2[is] <- system.time(for(i in 1:rep) sort(x, method = "quick"),
                            gcFirst = TRUE)[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)
    system.time(x1 <- sort(x, method = "shell"), gcFirst = TRUE)
    system.time(x2 <- sort(x, method = "quick"), gcFirst = TRUE)
    stopifnot(identical(x1, x2))
    ## End(Not run)

[Package base version 2.3.1 Index]