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

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