| % File src/library/base/man/maxCol.Rd |
| % Part of the R package, https://www.R-project.org |
| % Copyright 1995-2014 R Core Team |
| % Distributed under GPL 2 or later |
| |
| \name{maxCol} |
| \alias{max.col} |
| \title{Find Maximum Position in Matrix} |
| \description{ |
| Find the maximum position for each row of a matrix, breaking ties at random. |
| } |
| \usage{ |
| max.col(m, ties.method = c("random", "first", "last")) |
| } |
| \arguments{ |
| \item{m}{numerical matrix} |
| \item{ties.method}{a character string specifying how ties are |
| handled, \code{"random"} by default; can be abbreviated; see |
| \sQuote{Details}.} |
| } |
| \value{index of a maximal value for each row, an integer vector of |
| length \code{nrow(m)}. |
| } |
| \details{ |
| When \code{ties.method = "random"}, as per default, ties are broken at |
| random. In this case, the determination of a tie assumes that |
| the entries are probabilities: there is a relative tolerance of |
| \eqn{10^{-5}}{1e-5}, relative to the largest (in magnitude, omitting |
| infinity) entry in the row. |
| |
| If \code{ties.method = "first"}, \code{max.col} returns the |
| column number of the \emph{first} of several maxima in every row, the |
| same as \code{\link{unname}(\link{apply}(m, 1, \link{which.max}))}.\cr |
| Correspondingly, \code{ties.method = "last"} returns the \emph{last} |
| of possibly several indices. |
| } |
| \references{ |
| Venables, W. N. and Ripley, B. D. (2002) |
| \emph{Modern Applied Statistics with S.} |
| New York: Springer (4th ed). |
| } |
| \seealso{\code{\link{which.max}} for vectors. |
| } |
| \examples{ |
| table(mc <- max.col(swiss)) # mostly "1" and "5", 5 x "2" and once "4" |
| swiss[unique(print(mr <- max.col(t(swiss)))) , ] # 3 33 45 45 33 6 |
| |
| set.seed(1) # reproducible example: |
| (mm <- rbind(x = round(2*stats::runif(12)), |
| y = round(5*stats::runif(12)), |
| z = round(8*stats::runif(12)))) |
| \dontrun{ |
| [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10] [,11] [,12] |
| x 1 1 1 2 0 2 2 1 1 0 0 0 |
| y 3 2 4 2 4 5 2 4 5 1 3 1 |
| z 2 3 0 3 7 3 4 5 4 1 7 5 |
| } |
| ## column indices of all row maxima : |
| utils::str(lapply(1:3, function(i) which(mm[i,] == max(mm[i,])))) |
| max.col(mm) ; max.col(mm) # "random" |
| max.col(mm, "first") # -> 4 6 5 |
| max.col(mm, "last") # -> 7 9 11 |
| \dontshow{ |
| stopifnot(max.col(mm, "first") == c(4, 6, 5), |
| max.col(mm, "last") == c(7, 9, 11)) |
| } |
| } |
| \keyword{utilities} |
| \keyword{array} |