file.exists("C:/Explore/r-basics/Data/class_x.rdata")


load("C:/Explore/r-basics/Data/class_x.rdata")

class <- class_x
is.data.frame(class)
some_vars <-names(class) %in% c("height", "weight")
class_df <- class[some_vars]
is.data.frame(class_df)
sapply_output <- sapply(class_df, mean)
is.vector(sapply_output)
sapply_output

###################
lapply_output = lapply(class_df, mean)
is.list(lapply_output)
lapply_output
lapply_output[[2]]