Is it possible to include two functions within a single tapply or aggregate statement?
Below I use two tapply statements and two aggregate statements: one for mean and one for SD.
I would prefer to combine the statements.
my.Data = read.table(text = "
animal age sex weight
1 adult female 100
2 young male 75
3 adult male 90
4 adult female 95
5 young female 80
", sep = "", header = TRUE)
with(my.Data, tapply(weight, list(age, sex), function(x) {mean(x)}))
with(my.Data, tapply(weight, list(age, sex), function(x) {sd(x) }))
with(my.Data, aggregate(weight ~ age + sex, FUN = mean)
with(my.Data, aggregate(weight ~ age + sex, FUN = sd)
# this does not work:
with(my.Data, tapply(weight, list(age, sex), function(x) {mean(x) ; sd(x)}))
# I would also prefer that the output be formatted something similar to that
# show below. `aggregate` formats the output perfectly. I just cannot figure
# out how to implement two functions in one statement.
age sex mean sd
adult female 97.5 3.535534
adult male 90 NA
young female 80.0 NA
young male 75 NA
I can always run two separate statements and merge the output. I was just hoping there might be a slightly more convenient solution.
I found the answer below posted here: Apply multiple functions to column using tapply
f <- function(x) c(mean(x), sd(x))
do.call( rbind, with(my.Data, tapply(weight, list(age, sex), f)) )
However, neither the rows or columns are labeled.
[,1] [,2]
[1,] 97.5 3.535534
[2,] 80.0 NA
[3,] 90.0 NA
[4,] 75.0 NA
I would prefer a solution in base R. A solution from the plyr
package was posted at the link above. If I can add the correct row and column headings to the above output, it would be perfect.
But these should have:
with(my.Data, aggregate(weight, list(age, sex), function(x) { c(MEAN=mean(x), SD=sd(x) )}))
with(my.Data, tapply(weight, list(age, sex), function(x) { c(mean(x) , sd(x) )} ))
# Not a nice structure but the results are in there
with(my.Data, aggregate(weight ~ age + sex, FUN = function(x) c( SD = sd(x), MN= mean(x) ) ) )
age sex weight.SD weight.MN
1 adult female 3.535534 97.500000
2 young female NA 80.000000
3 adult male NA 90.000000
4 young male NA 75.
The principle to be adhered to is to have your function return "one thing" which could be either a vector or a list but cannot be the successive invocation of two function calls.