[R] idiom for constructing data frame

[Sarah Goslee]

On Tue, Mar 31, 2015 at 6:35 PM, Richard M. Heiberger <rmh at temple.edu> wrote:
> I got rid of the extra column.
>
> data.frame(r=seq(8), foo=NA, bar=NA, row.names="r")

Brilliant!

After much fussing, including a disturbing detour into nested lapply
statements from which I barely emerged with my sanity (arguable, I
suppose), here is a one-liner that creates a data frame of arbitrary
number of rows given an existing data frame as template for column
number and name:


n <- 8
df1 <- data.frame(A=runif(9), B=runif(9))

do.call(data.frame, setNames(c(list(seq(n), "r"), as.list(rep(NA,
ncol(df1)))), c("r", "row.names", colnames(df1))))

It's not elegant, but it is fairly R-ish. I should probably stop
hunting for an elegant solution now.

Thanks, everyone!

Sarah


> Rich
>
> On Tue, Mar 31, 2015 at 6:18 PM, Sven E. Templer <sven.templer at gmail.com> wrote:
>> If you don't mind an extra column, you could use something similar to:
>>
>> data.frame(r=seq(8),foo=NA,bar=NA)
>>
>> If you do, here is another approach (see function body):
>>
>> empty.frame <- function (r = 1, n = 1, fill = NA_real_) {
>>   data.frame(setNames(lapply(rep(fill, length(n)), rep, times=r), n))
>> }
>> empty.frame()
>> empty.frame(, seq(3))
>> empty.frame(8, c("foo", "bar"))
>>
>> I could not put it in one line either, without retyping at least one
>> argument (n in this case).
>> So I suggest a function is the way to go for a simplified syntax ...
>>
>> Thanks to all for the ideas!
>> Sven
>>
>> On 31 March 2015 at 20:55, William Dunlap <wdunlap at tibco.com> wrote:
>>
>>> You can use structure() to attach the names to a list that is input to
>>> data.frame.
>>> E.g.,
>>>
>>> dfNames <- c("First", "Second Name")
>>> data.frame(lapply(structure(dfNames, names=dfNames),
>>> function(name)rep(NA_real_, 5)))
>>>
>>>
>>> Bill Dunlap
>>> TIBCO Software
>>> wdunlap tibco.com
>>>
>>> On Tue, Mar 31, 2015 at 11:37 AM, Sarah Goslee <sarah.goslee at gmail.com>
>>> wrote:
>>>
>>> > Hi,
>>> >
>>> > Duncan Murdoch suggested:
>>> >
>>> > > The matrix() function has a dimnames argument, so you could do this:
>>> > >
>>> > > names <- c("strat", "id", "pid")
>>> > > data.frame(matrix(NA, nrow=10, ncol=3, dimnames=list(NULL, names)))
>>> >
>>> > That's a definite improvement, thanks. But no way to skip matrix()? It
>>> > just seems unRlike, although since it's only full of NA values there
>>> > are no coercion issues with column types or anything, so it doesn't
>>> > hurt. It's just inelegant. :)
>>> >
>>> > Sarah

-- 
Sarah Goslee
http://www.functionaldiversity.org