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

[Rui Barradas]

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
>

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.