How to apply function returning data.frames with factors to sequence

Question

How do I apply a function which returns a data.frame with factors to a sequence?

Example:

s <- factor(c(10, 20, 30))
t <- factor(c("a", "b", "a"))
v <- c(5, 6, 4)

df <- data.frame(s,t,v)

So the data.frame df is this:

   s t v
1 10 a 5
2 20 b 6
3 30 a 4

I also have a function which returns a data.frame:

simpleFunc2 <- function(df, x){
  tmp <- subset(df, df$s == x)
  return(tmp)
}

Now I have a sequence

x <- c(20, 30, 10, 30, 10)

and want to the result auf applying the function simpleFunc2 to this sequence.

I use sapply

sapply(x, function(x) simpleFunc2(df, x))

But I get

  [,1]     [,2]     [,3]     [,4]     [,5]    
s factor,1 factor,1 factor,1 factor,1 factor,1
t factor,1 factor,1 factor,1 factor,1 factor,1
v 6        4        5        4        5  

How do I get the right values of the factors back?

This example is simplified. So maybe there's a much simpler way to do it in this case.

Answer 1

I see you have gotten an answer to your question, but I think your approach to selecting the superset from that dataframe was too involved. (And my apologies if that function was not representative. I'd like to offer a method of extraction that is faster than going through subset:

> df[ match(x, df$s), ]
     s t v
2   20 b 6
3   30 a 4
1   10 a 5
3.1 30 a 4
1.1 10 a 5
# Save results as from:
> do.call(rbind, lapply(x, function(x) simpleFunc2(df, x)) )
    s t v
2  20 b 6
3  30 a 4
31 10 a 5
32 30 a 4
5  10 a 5

Answer 2

Try lapply instead with do.call as in:

do.call(rbind, lapply(x, function(x) simpleFunc2(df=df, x)))