Question

Why does “myclass” disapear in the following example?
How to avoid that?

#
library(xts)

# sample data
fo <- "%Y-%m-%d %X"
st <- Sys.time()
delta <- seq(from=0, by=10, length.out=10)
ma1 <- matrix(data=sin(delta/50), ncol=1, nrow=10)
ma2 <- matrix(data=sin(delta/25), ncol=1, nrow=10)
d1a <- xts(x=ma1, order.by=strptime(st, format=fo) + delta)
d2a <- xts(x=ma2, order.by=strptime(st, format=fo) + delta)
d1b <- xts(x=ma1, order.by=strptime(st, format=fo) + delta)
d2b <- xts(x=ma2, order.by=strptime(st, format=fo) + delta)
d1c <- xts(x=ma1, order.by=strptime(st, format=fo) + delta)
d2c <- xts(x=ma2, order.by=strptime(st, format=fo) + delta)

# original class
class(d1a)
class(d2a)
#
d3a <- d1a + d2a

# class
class(d1b) <- "myclass"
class(d2b) <- "myclass"
#
d3b <- d1b + d2b

# class
class(d1c) <- c("myclass","xts","zoo")
class(d2c) <- c("myclass","xts","zoo")
#
d3c <- d1c + d2c

#
class(d3a)
[1] "xts" "zoo"
class(d3b)
[1] "myclass"
class(d3c)
[1] "xts" "zoo" # expected was "myclass" "xts" "zoo"

Answer 1

EDIT: This is fixed in xts > 0.12.2

Now Ops.xts() retains the class of the objects that inherit from xts.

class(d3c)
[1] "myclass" "xts"     "zoo"

---

You haven’t defined a + method for myclass, so the xts method gets dispatched… and it always returns an xts-class object (unfortunately).

You can work around this by defining:

Ops.myclass <- xts:::Ops.xts