To select a subset of a variable

To select a subset of a variable based on the categories of other variables or condition in further analysis, we can do with the following code

For example we need to get the subset of variable age based on the gender 

age = c(45,50,60)

gender = c("F", "M","F")

maleage <- age[gender == "M"]

femaleage <- age[gender == "F"]