Is there a function like rollapply for data.frame [duplicate]

Question

Possible Duplicate:
Can `ddply` (or similar) do a sliding window?

Is there a function like rollapply (standard R or within a CRAN package) that operates on a data.frame, but doesn't convert it to a matrix. rollapply can be used with a data.frame, but if the data.frame has mixed types then each window of data is converted to a character (matrix).

I prefer a function that supports width, na.pad, align, etc. just like rollapply

Example

Take any data.frame with mixed-types

test = data.frame( Name = c( "bob" , "jane" , "joe" ) , Points = c( 4 , 9 , 1 ) )

Lets say you want to roll with window size 2. The first iteration of FUN is called with a data.frame that only includes rows 1 and 2 of test.

So RollapplyThatRespectsDataFrame( ... , FUN = function( x ) { ... } ) upon the first iteration would set x = data.frame( Name = c( "bob" , "jane" ) , Points = c( 4 , 9 ) )

The second iteration is a data.frame with rows 2 and 3 of test.

Basically this new function does the same thing as rollapply, except it works properly with data.frames. It doesn't convert to matrix.

Answer 1

Try this:

> library(zoo)
> DF <- data.frame(a = 1:10, b = 21:30, c = letters[1:10])
> replace(DF, 1:2, rollapply(DF[1:2], 3, sum, fill = NA))
    a  b c
1  NA NA a
2   6 66 b
3   9 69 c
4  12 72 d
5  15 75 e
6  18 78 f
7  21 81 g
8  24 84 h
9  27 87 i
10 NA NA j

Regarding the example that was added to the question after some discussion, such functionality can be layered on top of rollapply by applying it to the row indexes:

> lapply(as.data.frame(t(rollapply(1:nrow(test), 2, c))), function(ix)test[ix, ])
$V1
  Name Points
1  bob      4
2 jane      9

$V2
  Name Points
2 jane      9
3  joe      1

and here it is wrapped up a bit better:

rollapply.data.frame <- function(data, ..., fill = NULL, FUN, 
        simplify = function(x) do.call(rbind, x)) {
    fill0 <- if (!is.null(fill)) NA
    result <- lapply(
       as.data.frame(t(rollapply(1:nrow(data), ..., fill = fill0, FUN = c))), 
       function(ix) {if (all(is.na(ix))) fill else FUN(data[ix, ])}
    )
    simplify(result)
}

> rollapply(test, 2, FUN = identity, simplify = identity)
$V1
  Name Points
a  bob      4
b jane      9

$V2
  Name Points
b jane      9
c  joe      1

> rollapply(test, 2, FUN = identity, fill = NA, simplify = identity)
$V1
  Name Points
a  bob      4
b jane      9

$V2
  Name Points
b jane      9
c  joe      1

$V3
[1] NA