On Tue, Jun 17, 2008 at 9:28 AM, Tom Backer Johnsen <[EMAIL PROTECTED]> wrote:
> In a research project we are using a web-based tools for collecting data
> from questionnaire. The system generates files that are simple to read as a
> data frame in the "long" format, which are simple to convert to the "wide"
> format.
>
> Something that might happen are: (a) there are two (multiple) references to
> the same cell, and (b) if there are missing values? So, the data set has
> two references to S2/T2 and none to the S2/T1 combination:
>
>> d
> values person time
> 1 1 S1 T1
> 2 2 S1 T2
> 3 3 S1 T3
> 4 4 S1 T4
> 5 22 S2 T2
> 6 6 S2 T2
> 7 7 S2 T3
> 8 8 S2 T4
> 9 9 S3 T1
> 10 10 S3 T2
> 11 11 S3 T3
> 12 12 S3 T4
> reshape (d, idvar="person", v.names=c("values"), timevar="time",
> direction="wide")
> person values.T1 values.T2 values.T3 values.T4
> 1 S1 1 2 3 4
> 5 S2 NA 22 7 8
> 9 S3 9 10 11 12
>
> The missing cell gets an NA as expected. But the surprise is in the case
> where there are two references to the same cell. The the *first* is used
> (22 rather than 6).
You might try using the reshape package instead:
last <- function(x) x[length(x)]
names(d) <- c("value", "person", "time")
cast(d, person ~ time, last)
You can find out more at http://had.co.nz/reshape
Hadley
--
http://had.co.nz/
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