See the NEWS in R 1.5.0 and 150update.txt on developer.r-project.org
about testing equality of possibly missing values.
aa$x[4]=="x" is incorrect usage (and always has been). The result is
now
logical NA, and ifelse(NA, "a", "b") returns NA as the
answer is unknown.
Use %in% or identical().
On Mon, 13 May 2002, juli g. pausas wrote:
>
> I suppose this is a very basic question, but I cannot understant it:
>
> > aa <- data.frame(x = c(rep("x", 3), NA, NA, NA), y= 1:6)
> > aa$x[4]
> [1] <NA>
> Levels: x
> > aa$y[4]
> [1] 4
> > aa$y[4] <- ifelse(aa$x[4]=="x", NA, aa$y[4])
> > aa$y[4]
> [1] NA
> >
>
> I was expecting aa$y[4] not to be changed, but I may missundertood
> something.
>
> aa2 <- data.frame(x = c(rep("x", 3), rep("b", 3)),
y= 1:6)
> aa2$y <- ifelse(aa2$x=="x", NA, aa2$y)
>
> this works OK
>
> (R 1.5.0 on Windows)
>
> juli
>
>
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--
Brian D. Ripley, ripley at stats.ox.ac.uk
Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
University of Oxford, Tel: +44 1865 272861 (self)
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