Inconsistent conversions to/from zoo with zero-length coredata

[joshuaulrich]

Converting a zero-length object to zoo and back to xts loses the dim and dimname attributes.

# zero-length zoo
z <- zoo(matrix(numeric(0), 3, 3)[0,], numeric(0))

# can't convert to xts
as.xts(z)
### Error in xts(coredata(x), order.by = order.by, frequency = frequency,  :
###   order.by requires an appropriate time-based object

# zero-length xts
x <- .xts(matrix(numeric(0), 3, 3)[0,], numeric(0))

# can convert to zoo...
zx <- as.zoo(x)

# ...but can't convert back to xts
xzx <- as.xts(zx)
### Error in xts(coredata(x), order.by = order.by, frequency = frequency,  :
###   order.by requires an appropriate time-based object

This is partially caused by as.zoo.xts() setting coredata to NULL. It might also be related to the fix for #223.

[joshuaulrich]

It's not an issue that as.xts(z) doesn't work because z doesn't have a time-based index. It works if the index is time-based.

z <- zoo(matrix(numeric(0), 3, 3)[0,], .POSIXct(numeric(0)))
xz <- as.xts(z)

We have to change zoo:::as.zoo.xts() in order for all.equal(x, xzx) to be TRUE. It needs to only set y <- NULL if it's zero-length and has no dims.

The patch is:

diff --git a/pkg/zoo/R/as.zoo.R b/pkg/zoo/R/as.zoo.R
index d1a8c99..0f5dc42 100644
--- a/pkg/zoo/R/as.zoo.R
+++ b/pkg/zoo/R/as.zoo.R
@@ -52,7 +52,7 @@ as.zoo.timeSeries <- function(x, ...) {
 
 as.zoo.xts <- function(x, ...) {
   y <- coredata(x)
-  if (length(y) == 0) {
+  if (length(y) == 0 && is.null(dim(y))) {
     y <- NULL
   }
   zoo(y, order.by = index(x), ...)

[joshuaulrich]

This is fixed in zoo >= 1.8-12.

[zeileis]

Thanks, much appreciated.