Question

I want to rbind.zoo two zoo object together. When I was testing I came across the following issue(?)…

Note: The below is an example, there is clearly no point to it apart from being illustrative.
I have an zoo object, call it, ‘X’. I want to break it into two parts and then rbind.zoo them together. When I compare it to the original object then all.equal gives differences.

It appears that the ‘$class’ attribute differs, but I can’t see how or why. Is I make these xts objects then the all.equal works as expected.

i.e. …..

X.date <- as.POSIXct(paste("2003-", rep(1:4, 4:1), 
                     "-", sample(1:28, 10, replace = TRUE), sep = ""))

X <- zoo(matrix(rnorm(24), ncol = 2), X.date)

a <- X[c(1:3), ]      # first 3 elements

b <- X[c(4:6), ]      # second 3 elements

c <- rbind.zoo(a, b)  # rbind into an object of 6 elements

d <- X[c(1:6), ]      # all 6 elements

all.equal(c, d)       # are they equal?

~~~~

all.equal gives me the following difference:

“Attributes: < Component 3: Attributes: < Length mismatch: comparison on first 1 components > >”

Answer 1

Yes, you may have found a bug there in terms of the handling of attributes. On the other hand, who cares? c and d are effectively equal:

R> c - d

2003-01-07 0 0
2003-01-15 0 0
2003-01-17 0 0
2003-01-18 0 0
2003-02-17 0 0
2003-02-22 0 0
R> 

Inspecting the objects gives nothing away:

R> str(c)
‘zoo’ series from 2003-01-07 to 2003-02-22
  Data: num [1:6, 1:2] 0.79 -0.731 1.574 -0.694 0.358 ...
  Index:  POSIXct[1:6], format: "2003-01-07" "2003-01-15" 
      "2003-01-17" "2003-01-18" "2003-02-17" "2003-02-22"
R> str(d)
‘zoo’ series from 2003-01-07 to 2003-02-22
  Data: num [1:6, 1:2] 0.79 -0.731 1.574 -0.694 0.358 ...
  Index:  POSIXct[1:6], format: "2003-01-07" "2003-01-15" 
      "2003-01-17" "2003-01-18" "2003-02-17" "2003-02-22"

I suggest you send a polite mail to the maintainers of zoo illustrating the case.