Maybe this is simple but I can't find answer on web. I have problem with mean calculation by factors by level. My data looks typicaly:
factor, value
a,1
a,2
b,1
b,1
b,1
c,1
I want to get vector A contains mean only for level "a" If I type A on consol I want to get 1.5 And this method for calculating mean, must use factors.
Thank you in advance for help.
Just for fun posting the data.table solution although you probably should do what @lukeA suggested
library(data.table)
A <- setDT(df)[factor == "a", mean(value)]
## [1] 1.5