On 2018-09-26 15:34, Duncan Murdoch wrote:
On 26/09/2018 4:16 PM, Spencer Graves wrote:
Is there anything comparable to "with" for S4 objects?
EXAMPLE:
A "Wave" object in the tuneR package has slots "left" and
"right", plus others. I'd like to be able to do something like the
following:
library(tuneR)
x <- seq(0, 2*pi, length = 6)
all.equal(x, rev(x))
channel <- round(32000 * sin(440 * x))
Wobj <- Wave(left = channel, right=rev(channel))
with(Wobj, quantile(left-right))
** This last statement throws "Error ... object 'left' not
found".
Is there something comparable to "with" that can do this?
I don't know of anything that is "officially sanctioned". A couple of
ideas:
1. Slots in S4 are stored in attributes. So
with(attributes(Wobj), quantile(left - right))
works. BUT: as far as I recall, this is an undocumented
implementation detail, and you aren't supposed to count on it.
2. You could write an as.list() method for the Wave class, then
with(as.list(Wobj),
would work. This may be the "right" way to do this.
Thanks. I'd prefer to have as.list.default convert every S4
object to a list. And have with(S4_object, ...) interpret it equivalent
to with(as.list(S4_object), ...).
I think I'll do it other ways for the time being.
Best Wishes,
Spencer
Duncan Murdoch
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