Hi,
I was hoping someone could help me with the following problem. Consider this
toy example. For the input dataset there are four individuals (rows "indv.1"
through "indv.4"), measured for two different variables (columns "var.1" and
"var.2") at two different levels of a factor (column "factor.level"). I want to
calculate a matrix that has the average values for each trait (rows "var1.avg"
and "var2.avg") separated by each level of the factor (columns "factor.a" and
"factor.b").
Please try my code below. I'm stuck at the part where I write the averages for
each trait to the output matrix (see "y[j,i] <- mean(d[,j])" below). I think my
code is wrong at this step, but I don't know how to do it right. To put it
another way, why does my final product (the matrix called "y") have no values
in it?
My real dataset has many more variables (210) and many more factors
(10) than this toy example, so any coding strategy must scale up well. Thanks
very much in advance!
x <- read.table(textConnection("var.1 var.2 factor.level
indv.1 3 4 a
indv.2 8 7 a
indv.3 4 3 b
indv.4 0 9 b"), header = TRUE)
y <- matrix(nrow = 2, ncol = 2)
colnames(y) <- c("factor.a", "factor.b")
rownames(y) <- c("var1.avg", "var2.avg")
for(i in 1:2) {
by(x, x$factor.level, function(d) {
for (j in 1:2) {
y[j,i] <- mean(d[,j])
}
}
)
}
y
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