xts subsetting gives incorrect results for months

问题

I am using R 3.2.1 for Mac OS X and seem to have run into incorrect behavior in xts subsetting. In brief, subsetting monthly data give a result that is 1 month lagged from what it should be. Here is a simple example that is similar to an analysis of paleotemperature I am doing:

First I will make some test data for the example:

xts.test <- xts(rnorm(440*12, mean=0, sd=10),order.by=timeBasedSeq(155001/1989))

This produces a correct xts file AFAICT. Here is the first year of 12 months.

head(xts.test, 12L)

               [,1]
Jan 1550 -6.9301845  
Feb 1550 12.1581413  
Mar 1550  3.9688139  
Apr 1550  3.9540268  
May 1550  9.8200923  
Jun 1550 -4.2090998  
Jul 1550  7.5950340  
Aug 1550 -6.5967389  
Sep 1550 -0.6736532  
Oct 1550  6.4939221  
Nov 1550  4.3916465  
Dec 1550 19.8800872

However, when I try to subset this by selecting for a single year, I get the following:

xts.test["1550"]

               [,1]
Feb 1550 12.1581413  
Mar 1550  3.9688139  
Apr 1550  3.9540268  
May 1550  9.8200923  
Jun 1550 -4.2090998  
Jul 1550  7.5950340  
Aug 1550 -6.5967389  
Sep 1550 -0.6736532  
Oct 1550  6.4939221  
Nov 1550  4.3916465  
Dec 1550 19.8800872  
Jan 1551 -2.9549224

That is, instead of the correct Jan-Dec 1550, I get Feb 1550 through Jan 1551

I get a similar lag when I try to subset by selecting months of a year. c(2, 3,4,5,6,7) get me April through September instead of March through August.

Any thoughts here?

回答1:

This is a bug that has been fixed in the most recent development version on GitHub.

R> require(xts)
R> xts.test <- xts(rnorm(440*12, mean=0, sd=10),order.by=timeBasedSeq(155001/1989))
R> packageVersion("xts")
[1] ‘0.9.7’
R> str(xts.test)  # notice TZ is not set
An ‘xts’ object on Jan 1550/Dec 1989 containing:
  Data: num [1:5280, 1] -8.11 -7.65 2.07 -3.29 17.03 ...
  Indexed by objects of class: [yearmon] TZ: 
  xts Attributes:  
 NULL

Notice that TZ is not set above, but it's set in the new version below.

R> packageVersion("xts")
[1] ‘0.9.8’
R> str(xts.test)  # notice TZ is set
An ‘xts’ object on Jan 1550/Dec 1989 containing:
  Data: num [1:5280, 1] 0.357 12.318 24.291 22.181 6.123 ...
  Indexed by objects of class: [yearmon] TZ: UTC
  xts Attributes:  
 NULL

来源：https://stackoverflow.com/questions/31777724/xts-subsetting-gives-incorrect-results-for-months

标签

time-series

subset

xts