R-listers,

I am using xts with a yearmon index, but am getting some inconsistent
results with the date index when i drop observations (for example by using
na.omit).

The issue is illustrated in the example below.  If I start with a monthly
zooreg series starting in 2009, yearmon converts this to "Dec-2008".  Not
such a worry for my example, but strange.  Having converted to xts, i drop
the first observation.  The index shows jan 2009.  But if i create a new
variable with this index, it shifts the series back to dec 2008.

No doubt i am doing something wrong.  very grateful for any tips

library(xts)

z <- zooreg(1:24,frequency=12,start=c(2009,1))  # monthly data starting 2009
x <- xts(z,as.yearmon(index(z)))                        # starts Dec 2008
xx <- x[-1,  ]                                                      # drop
first obs (eg through na.omit)
index(xx)                                                         # starts
jan 2009
xxx <- xts(NA[1:length(xx)],index(xx))                # back to dec 2008

periodicity(x)
periodicity(xx)
periodicty(xxx)

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