R help - Mar 2010 - How to handle missing value as first item in yearmon (zoo package)

Hi,

Some time series have missing values in the time index. For example 
historical data on business cycles will typically date them from peak to 
trough, but some information may be missing. In most cases, this does 
not cause trouble,
but if the first date is missing (e.g., we know the date of the first 
trough but not the earlier peak), we want the first element in a list of 
dates to be NA. Using yearmon, this causes trouble. Consider this:

 > x <- as.yearmon("March 2010","%B %Y")
 > y <- c(x,NA)
 > z <- c(NA,x)
 > y <- yearmon(y)
 > z <- yearmon(z)
 > y
         [1] "Mar 2010" NA
 > z
     Error in charToDate(x) :
       character string is not in a standard unambiguous format

Can someone explain how to make an object of type yearmon with a missing 
value in its first element?

Thanks.

     Marsh Feldman

There is a bug in as.Date.yearmon and as.Date.yearqtr which is
triggered by certain NAs.  Its now fixed in the development version of
zoo on R-forge.  Note that in your code it only affecting printing of
the yearmon variable.  The yearmon variable itself is correct.

Try this:

source("http://r-forge.r-project.org/plugins/scmsvn/viewcvs.php/*checkout*/pkg/zoo/R/yearmon.R?rev=686&root=zoo")
x <- as.yearmon("March 2010","%B %Y")
z <- yearmon(c(NA, x))
z


On Fri, Mar 19, 2010 at 9:36 AM, Marshall Feldman <marsh at uri.edu>
wrote:
> Hi,
>
> Some time series have missing values in the time index. For example
> historical data on business cycles will typically date them from peak to
> trough, but some information may be missing. In most cases, this does not
> cause trouble,
> but if the first date is missing (e.g., we know the date of the first
trough
> but not the earlier peak), we want the first element in a list of dates to
> be NA. Using yearmon, this causes trouble. Consider this:
>
>> x <- as.yearmon("March 2010","%B %Y")
>> y <- c(x,NA)
>> z <- c(NA,x)
>> y <- yearmon(y)
>> z <- yearmon(z)
>> y
> ? ? ? ?[1] "Mar 2010" NA
>> z
> ? ?Error in charToDate(x) :
> ? ? ?character string is not in a standard unambiguous format
>
> Can someone explain how to make an object of type yearmon with a missing
> value in its first element?
>
> Thanks.
>
> ? ?Marsh Feldman
>
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