One of the things you have to be careful about with R is the automatically assigned names. It’s usually not too bad, but there are plenty of times you’ll find yourself frustrated. Here’s one of them:
> z <- c(a=1.5, b=2.5)
> z
a b
1.5 2.5
Works as expected. I specified the names a and b for the elements of z, and that’s what I got.
> x <- 1.5
> y <- 2.5
> z <- c(a=x, b=y)
> z
a b
1.5 2.5
Again, works as expected. Now try this:
> w <- c(j=1.5, k=2.9)
> z <- c(a=w["j"], b=2.5)
> z["a"]
<NA>
NA
What the heck? Of course I’ve defined z["a"].
> z
a.j b
1.5 2.5
It turns out that I haven’t. I’ve defined z["a.j"]. I understand the reasoning behind this decision. The goal is avoiding information loss. The reason this is so unintuitive is because I’ve explicitly specified that the name should be a, but the language took that as only a suggestion, giving an element that doesn’t have the name I wanted and expected. Furthermore, there is inconsistency, because this usually works.
One way to fix this is to use an unreasonably verbose syntax:
> z <- c(a=numeric(w["j"]), b=2.5)
> z
a b
0.0 2.5
I have a utility function for this situation:
c.named <- function(...) {
obj <- list(...)
result <- if (is.double(obj[[1]])) {
tmp <- numeric(length(obj))
for (ii in 1:length(obj)) {
tmp[ii] <- obj[[ii]]
}
tmp <- as.numeric(tmp)
tmp
} else if (is.integer(obj[[1]])) {
tmp <- integer(length(obj))
for (ii in 1:length(obj)) {
tmp[ii] <- obj[[ii]]
}
tmp <- as.integer(tmp)
tmp
} else if (is.logical(obj[[1]])) {
tmp <- logical(length(obj))
for (ii in 1:length(obj)) {
tmp[ii] <- obj[[ii]]
}
tmp <- as.logical(tmp)
tmp
} else {
tmp <- character(length(obj))
for (ii in 1:length(obj)) {
tmp[ii] <- obj[[ii]]
}
tmp <- as.character(tmp)
tmp
}
names(result) <- names(obj)
return(result)
}
You can verify that it fixes the problem:
> z <- c.named(a=w["j"], b=2.5)
> z
a b
1.5 2.5
While this should be the default behavior, it’s not, so I do use this function a fair amount. It will likely end up in my tstools package, even though there’s nothing specific about time series.