On Jan 30, 2010, at 9:22 AM, Dipankar Basu wrote:
Hi All,
I have a very simple question about a time series object: how to
access
values for a particular year and quarter (say)?
Suppose, following
http://www.stat.pitt.edu/stoffer/tsa2/R_time_series_quick_fix.htm
I have read in data as a time series; here is how it looks.
* Qtr1 Qtr2 Qtr3 Qtr4
1960 0.71 0.63 0.85 0.44
1961 0.61 0.69 0.92 0.55
. . . . .
. . . . .
1979 14.04 12.96 14.85 9.99
1980 16.20 14.67 16.02 11.61*
How do I access the value for 1961 quarter 3 (say)?
Time series (at least as I understand them) are vectors or matrices
with a folded and labeled print method but they are not referenced by
the marginal indices that are offered in the print method. Assuming
you followed that set of examples and have a time series named, jj,
the specific element could be accessed as:
> yr=1961
> qtr=3
> jj[ 4*(yr-1960)+qtr ]
[1] 0.92
Or if you wanted to extract the start year programmatically:
> jj[4*(yr-attr(jj, "tsp")[1])+qtr]
[1] 0.92
> jj[4*(yr-start(jj))+qtr]
[1] 0.92 NA
That NA comes from the return values of 1960 and 1 using start. The
help page for start has no section that describes the values, but it
appears that you get both the year and qtr.
> jj[4*(yr-start(jj)[1])+qtr]
[1] 0.92 # what I expected
--
David Winsemius, MD
Heritage Laboratories
West Hartford, CT
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