R：将函数应用于DataFrame

Question

I have following code:

library(Ecdat)
data(Fair)
Fair[1:5,]

x1 = function(x){
  mu = mean(x)
  l1 = list(s1=table(x),std=sd(x))
  return(list(l1,mu))
}

mylist <- as.list(Fair$occupation,
               Fair$education)

x1(mylist)

What I wanted is that x1 outputs the result for the items selected in mylist. However, I get In mean.default(x) : argument is not numeric or logical: returning NA .

Answer 1

You need to use lapply if your passing a list to a function

output<-lapply(mylist,FUN=x1)

This will process your function x1 for each element in mylist and return a list of results to output.

Answer 2

Here the mylist is created not in the correct way and a list is not needed also as data.frame is a list with columns of equal length. So, just subset the columns of interest and apply the function

lapply(Fair[c("occupation", "education")], x1)

---

In the OP's code, as.list simply creates a list of length 601 with only a single element in each.

str(mylist)
#List of 601
#$ : int 7
#$ : int 6
#$ : int 1
#...
#...

Another problem in the code is that it is not even considering the 2nd argument. Using a simple example

as.list(1:3, 1:2)
#[[1]]
#[1] 1

#[[2]]
#[1] 2

#[[3]]
#[1] 3

The second argument is not at all considered. It could have been

list(1:3, 1:2)
#[[1]]
#[1] 1 2 3

#[[2]]
#[1] 1 2

But for data.frame columns, we don't need to explicitly call the list as it is a list of vectors that have equal length.

Regarding the error in OP's post, mean works on vector s and not on list or data.frame .