[R] Expanding rows of a data frame into multiple rows

[Dennis Murphy]

Here's another approach using the plyr package:

# Function to process each row of input:
g <- function(d) {
    y <- unlist(d$observations)
    if(length(y) > 0)
      data.frame(site = d$site, sector = d$sector, y = y) else NULL
  }

library('plyr')
> ddply(input, .(site), g)
   site sector  y
1     1  north  1
2     1  north  2
3     1  north  3
4     2  south  4
5     2  south  3
6     4   west 14
7     4   west 12
8     4   west 53
9     4   west  2
10    4   west  4
11    5   east  3
12    6  south 23

HTH,
Dennis

On Sat, Oct 22, 2011 at 4:51 PM, Peter Meilstrup
<peter.meilstrup at gmail.com> wrote:
> The setup: I have a data frame where one column is in list mode, and
> each entry contains a vector of varying length.
> I want to expand this into a data frame with one row for each member
> of the list-mode column (the other values being replicated)
>
> For example, an example input and the desired output would be:
>
>  input <- data.frame(site = 1:6,
>                      sector = factor(c("north", "south", "east",
> "west", "east", "south")),
>                      observations =
> I(list(c(1,2,3),c(4,3),c(),c(14,12,53,2,4),c(3),c(23))))
>
>  desired.output <-
>    data.frame(site = c(1,1,1,2,2,4,4,4,4,5,6),
>               sector = factor(c(2,2,2,3,3,4,4,4,4,4,1,3),
>                               labels = c("east", "north", "south", "west")),
>               observations = c(1,2,3,4,3,14,12,53,2,4,3,23))
>
> There seems like there ought to be a good (simple, fast) way to do
> this, but I've been struggling. Any ideas?
>
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