I'd go a bit further and remind that the r-help posting guide is clear :
" For questions about functions in standard packages distributed with R
(see the FAQ Add-on packages in R), ask questions on R-help.
If the question relates to a contributed package , e.g., one downloaded from
CRAN, try contacting the package maintainer first. You can also use
find("functionname") and packageDescription("packagename") to find this
information. ONLY send such questions to R-help or R-devel if you get no
reply or need further assistance. This applies to both requests for help and
to bug reports. "
The "ONLY" is in bold in the posting guide. I changed the bold to capitals
above for people reading this in text only.
Since Tom and I are friendly and responsive, users of data.table don't
usually make it to r-help. We'll follow up this one off-list. Please note
that Rob's question is very good by the rest of the posting guide, so no
complaints there, only that it was sent to the wrong place. Please keep the
questions coming, but send them to us, not r-help.
You do sometimes see messages to r-help starting something like "I have
contacted the authors/maintainers but didn't hear back, does anyone know
...". To not state that they had would be an implicit request for further
work by the community (for free) to ask if they had. So its not enough to
contact the maintainer first, but you also have to say that you have as
well, and perhaps how long ago too would be helpful. For r-forge projects I
usually send any question to everyone on the project (easy to find) or if
they have a list then to that.
HTH
Matthew
"Tom Short" <tshort.rli...@gmail.com> wrote in message
news:fd27013a1003021718w409acb32r1281dfeca5593...@mail.gmail.com...
On Tue, Mar 2, 2010 at 7:09 PM, Rob Forler <rfor...@uchicago.edu> wrote:
> Hi everyone,
>
> I have the following code that works in data frames taht I would like tow
> ork in data.tables . However, I'm not really sure how to go about it.
>
> I basically have the following
>
> names = c("data1", "data2")
> frame = data.frame(list(key1=as.integer(c(1,2,3,4,5,6)),
> key2=as.integer(c(1,2,3,2,5,6)),data1 = c(3,3,2,3,5,2), data2=
> c(3,3,2,3,5,2)))
>
> for(i in 1:length(names)){
> frame[, paste(names[i], "flag")] = frame[,names[i]] < 3
>
> }
>
> Now I try with data.table code:
> names = c("data1", "data2")
> frame = data.table(list(key1=as.integer(c(1,2,3,4,5,6)),
> key2=as.integer(c(1,2,3,2,5,6)),data1 = c(3,3,2,3,5,2), data2=
> c(3,3,2,3,5,2)))
>
> for(i in 1:length(names)){
> frame[, paste(names[i], "flag"), with=F] = as.matrix(frame[,names[i],
> with=F] )< 3
>
> }
Rob, this type of question is better for the package maintainer(s)
directly rather than R-help. That said, one answer is to use list
addressing:
for(i in 1:length(names)){
frame[[paste(names[i], "flag")]] = frame[[names[i]]] < 3
}
Another option is to manipulate frame as a data frame and convert to
data.table when you need that functionality (conversion is quick).
In the data table version, frame[,names[i], with=F] is the same as
frame[,names[i], drop=FALSE] (the answer is a list, not a vector).
Normally, it's easier to use [[]] or $ indexing to get this. Also,
fname[i,j] <- something assignment is still a bit buggy for
data.tables.
- Tom
Tom Short
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