maxCol
Find Maximum Position in Matrix
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
 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
$1e5$, 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

length
nrow(m)
.
References
Venables, W. N. and Ripley, B. D. (2002) Modern Applied Statistics with S. New York: Springer (4th ed).
See Also
which.max
for vectors.
Examples
library(base)
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
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