In case anyone with a similar need comes across this thread, I am posting
below a solution to my problem, in which I construct a new data frame that
has the desired dimensions, instead of trying to change the dimensions of
the existing data frame.
<code>
npt <- length(pt)
# Step through each variable.
data.names <- names(x$data)
data.new <- as.data.frame(array(NA, dim=c(npt, dim(x$data)[2])))
names(data.new) <- data.names
for (datum.name in data.names) {
if (datum.name != "pressure") {
data.new[[datum.name]] <- approx(x$data[["pressure"]],
x$data[[datum.name]], pt)$y
}
}
# Now replace pressure
data.new[["pressure"]] <- pt
res$data <- data.new
</code>