Menu
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.
938
Factors are the variables that experimenters control during an experiment in order to determine their effect on the response variable. A factor can take on only a small number of values, which are known as factor levels.
The number of levels of a factor or independent variable is equal to the number of variations of that factor that were used in the experiment. If an experiment compared the drug dosages 50 mg, 100 mg, and 150 mg, then the factor "drug dosage" would have three levels: 50 mg, 100 mg, and 150 mg.
Hint: To find the mean of all factors of 10, we will write down the factors of 10. Factors of 10 are 1,2,5,10. We can use the formula Mean=Sum of the termsNumber of terms to find the mean.
Factors in R. Factors are data structures in R that store categorical data. They have a levels attribute that holds all the possible values that elements of the factor can take. R factors can be of any type. They only allow values permitted by the levels.
take a look at tapply, which lets you break up a vector according to a factor(s) and apply a function to each subset
> dat<-data.frame(factor=sample(c("a","b","c"), 10, T), value=rnorm(10)) > r1<-with(dat, tapply(value, factor, mean)) > r1 a b c 0.3877001 -0.4079463 -1.0837449 > r1[["a"]] [1] 0.3877001 You can access your results using r1[["a"]] etc.
Alternatively, one of the popular R packages (plyr) has very nice ways of doing this.
> library(plyr) > r2<-ddply(dat, .(factor), summarize, mean=mean(value)) > r2 factor mean 1 a 0.3877001 2 b -0.4079463 3 c -1.0837449 > subset(r2,factor=="a",select="mean") mean 1 0.3877001 You can also use dlply instead (which takes a dataframe and returns a list instead)
> dlply(dat, .(factor), summarize, mean=mean(value))$a mean 1 0.3877001 The following code asks for the mean of value when factor = a:
mean(data$value[data$factor == "a"]) If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With
