rank                  package:base                  R Documentation

Sample Ranks

Description:

     Returns the sample ranks of the values in a vector. Ties, i.e.,
     equal values, result in ranks being averaged, by default.

Usage:

     rank(x, na.last = TRUE,
          ties.method = c("average", "first", "random", "max", "min"))

Arguments:

       x: a numeric, complex, character or logical vector.

 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; if '"keep"' they are kept.

ties.method: a character string specifying how ties are treated, see
          below; can be abbreviated.

Details:

     If all components are different, the ranks are well defined, with
     values in '1:n' where 'n <- length(x)' and we assume no 'NA's for
     the moment.  Otherwise, with some values equal, called 'ties', the
     argument 'ties.method' determines the result at the corresponding
     indices.  The '"first"' method results in a permutation with
     increasing values at each index set of ties.  The '"random"'
     method puts these in random order whereas the default,
     '"average"', replaces them by their mean, and '"max"' and '"min"'
     replaces them by their maximum and minimum respectively, the
     latter being the typical "sports" ranking.

References:

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

See Also:

     'order' and 'sort'.

Examples:

     (r1 <- rank(x1 <- c(3, 1, 4, 15, 92)))
     x2 <- c(3, 1, 4, 1, 5, 9, 2, 6, 5, 3, 5)
     names(x2) <- letters[1:11]
     (r2 <- rank(x2)) # ties are averaged

     ## rank() is "idempotent": rank(rank(x)) == rank(x) :
     stopifnot(rank(r1) == r1, rank(r2) == r2)

     ## ranks without averaging
     rank(x2, ties.method= "first")  # first occurrence wins
     rank(x2, ties.method= "random") # ties broken at random
     rank(x2, ties.method= "random") # and again

     ## keep ties ties, no average
     (rma <- rank(x2, ties.method= "max"))  # as used classically
     (rmi <- rank(x2, ties.method= "min"))  # as in Sports
     stopifnot(rma + rmi == round(r2 + r2))

