ldply rename variables

[Ross Ahmed]

Does the output from ldply allow variables to be named, for example:

ldply(mtcars, function(x) mean(x))

gives a dataframe with column names automatically assigned to '.id' and 'V1'. Can the columns names be stated within the ldply function (as in ddply)?

[Brandon Hurr]

ldply(mtcars, function(model) {c(variablename=mean(model))})

It looks like it has to be wrapped a bit. 

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[Ista Zahn]

The documentation says

"The most unambiguous behaviour is achieved when ‘.fun’ returns a
data frame - in that case pieces will be combined with
‘rbind.fill’. If ‘.fun’ returns an atomic vector of fixed length,
it will be ‘rbind’ed together and converted to a data frame. Any
other values will result in an error."

So in my view the better way is

ldply(mtcars, function(x) data.frame(mean=mean(x)))

Best,
Ista

[Hadley Wickham]

> "The most unambiguous behaviour is achieved when ‘.fun’ returns a
> data frame - in that case pieces will be combined with
> ‘rbind.fill’. If ‘.fun’ returns an atomic vector of fixed length,
> it will be ‘rbind’ed together and converted to a data frame. Any
> other values will result in an error."
>
> So in my view the better way is
>
> ldply(mtcars, function(x) data.frame(mean=mean(x)))

Or ldply(mtcars, "mean"), since there the name of the function is known.

Hadley

--
Chief Scientist, RStudio
http://had.co.nz/

[Ista Zahn]

On Wed, Feb 13, 2013 at 7:41 AM, Hadley Wickham <h.wi...@gmail.com> wrote:
>> "The most unambiguous behaviour is achieved when ‘.fun’ returns a
>> data frame - in that case pieces will be combined with
>> ‘rbind.fill’. If ‘.fun’ returns an atomic vector of fixed length,
>> it will be ‘rbind’ed together and converted to a data frame. Any
>> other values will result in an error."
>>
>> So in my view the better way is
>>
>> ldply(mtcars, function(x) data.frame(mean=mean(x)))
>
> Or ldply(mtcars, "mean"), since there the name of the function is known.

Right! I always forget about that.