[R] fill 0-row data.frame with 1 line of NAs

[David Winsemius]

On Jul 10, 2012, at 2:05 PM, Rui Barradas wrote:

> Hello,
>
> Em 10-07-2012 18:59, Peter Ehlers escreveu:
>> On 2012-07-10 08:50, Brian Diggs wrote:
>>> On 7/10/2012 7:53 AM, Peter Ehlers wrote:
>>>> On 2012-07-10 06:57, Rui Barradas wrote:
>>>>> Hello,
>>>>>
>>>>> If you write a function, it becomes less convoluted...
>>>>>
>>>>>
>>>>> empty <- function(x){
>>>>>     if(NROW(x) == 0){
>>>>>         y <- rep(NA, NCOL(x))
>>>>>         names(y) <- names(x)
>>>>>         y
>>>>>     }else x
>>>>> }
>>>>>
>>>>> (.xb <- iris[ iris$Species=='zz', ])
>>>>> empty(.xb)
>>>>
>>>> Both this and Liviu's original solution destroy the
>>>> factor nature of 'Species' (which may not matter, of
>>>> course). How about
>>>>
>>>>    (.xb <- iris[ iris$Species=='zz', ])
>>>>    .xb <- .xb[1, ]   # this probably shouldn't work, but it does.
>>>
>>> Using NA subscripting seems even better
>>
>> Yes, you can subset with NA or any real number greater than 1.
>>
>> Peter Ehlers
>>

It would be difficult to be more compact than this:

 > iris[1, ][NA,]
    Sepal.Length Sepal.Width Petal.Length Petal.Width Species
NA           NA          NA           NA          NA    <NA>

--  
David

>
> Good to know,  was completely unaware of this indexing possibility.
>
> Rui Barradas
>
>>>
>>> empty <- function(x) {
>>>    if(NROW(x) == 0) {
>>>      x[NA,]
>>>    } else {
>>>      x
>>>    }
>>> }
>>>
>>> It even preserves the factor nature of things:
>>>
>>>  > empty(iris[iris$Specis=='zz',])
>>>     Sepal.Length Sepal.Width Petal.Length Petal.Width Species
>>> NA           NA          NA           NA          NA    <NA>
>>>  > str(empty(iris[iris$Specis=='zz',]))
>>> 'data.frame':   1 obs. of  5 variables:
>>>   $ Sepal.Length: num NA
>>>   $ Sepal.Width : num NA
>>>   $ Petal.Length: num NA
>>>   $ Petal.Width : num NA
>>>   $ Species     : Factor w/ 3 levels "setosa","versicolor",..: NA
>>>
>>>
>>>> ?
>>>>
>>>> Peter Ehlers
>>>>
>>>>>
>>>>>
>>>>> Hope this helps,
>>>>>
>>>>> Rui Barradas
>>>>>
>>>>> Em 10-07-2012 14:15, Liviu Andronic escreveu:
>>>>>> Dear all
>>>>>> Is there a simpler method to achieve the following: When I  
>>>>>> obtain an
>>>>>> empty data.frame after subsetting, I need for it to contain one  
>>>>>> line
>>>>>> of NAs. Here's a dummy example:
>>>>>>> (.xb <- iris[ iris$Species=='zz', ])
>>>>>> [1] Sepal.Length Sepal.Width  Petal.Length Petal.Width  Species
>>>>>> <0 rows> (or 0-length row.names)
>>>>>>> dim(.xb)
>>>>>> [1] 0 5
>>>>>>> (.xa <- data.frame(matrix(rep(NA, ncol(.xb)), 1)))
>>>>>>     X1 X2 X3 X4 X5
>>>>>> 1 NA NA NA NA NA
>>>>>>> names(.xa) <- names(.xb)
>>>>>>> (.xb <- .xa)
>>>>>>     Sepal.Length Sepal.Width Petal.Length Petal.Width Species
>>>>>> 1           NA          NA           NA          NA      NA
>>>>>>
>>>>>>
>>>>>> The solution I came up with is way too convoluted. Anything  
>>>>>> simpler?
>>>>>> Regards
>>>>>> Liviu
>>>>>>
>>>>>>
>>>>>
>>>>> ______________________________________________
>>>>> R-help at r-project.org mailing list
>>>>> https://stat.ethz.ch/mailman/listinfo/r-help
>>>>> PLEASE do read the posting guide
>>>>> http://www.R-project.org/posting-guide.html
>>>>> and provide commented, minimal, self-contained, reproducible code.
>>>>>
>>>>
>>>
>>>
>>
>> ______________________________________________
>> R-help at r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide
>> http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.

David Winsemius, MD
Heritage Laboratories
West Hartford, CT