# maxCol

0th

Percentile

##### Find Maximum Position in Matrix

Find the maximum position for each row of a matrix, breaking ties at random.

Keywords
utilities, array
##### Usage
max.col(m, ties.method = c("random", "first", "last"))
##### Arguments
m

numerical matrix

ties.method

a character string specifying how ties are handled, "random" by default; can be abbreviated; see ‘Details’.

##### Details

When 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 $10^{-5}$, relative to the largest (in magnitude, omitting infinity) entry in the row.

If ties.method = "first", max.col returns the column number of the first of several maxima in every row, the same as unname(apply(m, 1, which.max)). Correspondingly, ties.method = "last" returns the last of possibly several indices.

##### Value

index of a maximal value for each row, an integer vector of length nrow(m).

##### References

Venables, W. N. and Ripley, B. D. (2002) Modern Applied Statistics with S. New York: Springer (4th ed).

which.max for vectors.
library(base) # NOT RUN { 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)))) # } # NOT RUN { [,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 # } # NOT RUN { ## 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 # }