# maxCol: Find Maximum Position in Matrix

## Description

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

## Usage

 `1` ```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 1e-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.
 ``` 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19``` ```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 ## End(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 ```