I'm writing an expression that requires searching a vector according to
group. As an example, I want to find the maximum value in each of 5
groups.
group=rep(1:5, each=5) # create grouping variable
variable=rnorm(25) # generate data
d <- data.frame(group,variable) # make data frame
max(d$variable[d$group]) # try expression that
doesn't work
I'm expecting a vector containing the maximum variable value, per group.
What am I doing wrong? I know I can use aggregate, tapply, etc. but that
seems awkward and bulky, is there a simpler way?
Dr. Seth W. Bigelow
Biologist, USDA-FS Pacific Southwest Research Station
1731 Research Park Drive, Davis California
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