[R] Extending a vector to length n

[Richard.Cotton at hsl.gov.uk]

> In general, how can I increase a vector of length m (< n) to length n
> by padding it with m - n missing values, without losing attributes?
> The two approaches I've tried, using length<- and adding missings with
> c, do not work in general:
> 
> > a <- as.Date("2008-01-01")
> > c(a, NA)
> [1] "2008-01-01" NA
> > length(a) <- 2
> > a
> [1] 13879    NA
> 
> 
> > b <- factor("a")
> > c(b, NA)
> [1]  1 NA
> > length(b) <- 2
> > b
> [1] a    <NA>
> Levels: a

You can save the attributes to a new variable, increase the length, then 
reapply the attributes, e.g.

extend <- function(x, n)
{
   att <- attributes(x)
   length(x) <- n
   attributes(x) <- att
   x
}

a <- as.Date("2008-01-01")
extend(a, 2)
# [1] "2008-01-01" NA

b <- factor("a")
extend(b, 2)
# [1] a    <NA>
# Levels: a

It would, perhaps, be nicer if length had an option to preserve 
attributes.

Regards,
Richie.

Mathematical Sciences Unit
HSL


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