subsetting in xts using a parameter holding dates

问题:

I am familiar with the xts subsetting abilities. However, I can't find an elegant way to subset a parameterized range of dates. something like this:

times = c(as.POSIXct("2012-11-03 09:45:00 IST"),
          as.POSIXct("2012-11-05 09:45:00 IST"))

#create an xts object:
xts.obj = xts(c(1,2),order.by = times)

#filter with these dates:
start.date = as.POSIXct("2012-11-03")
end.date = as.POSIXct("2012-11-04")

#instead of xts["2012-11-03"/"2012-11-04"], do something like this:
xts[start.date:end.date]

Does anybody have any idea? Thanks!

回答1:

You could paste the start.date and end.date objects together, separating by "::" or "/", and then use that to subset.

R> xts.obj[paste(start.date,end.date,sep="::")]
                    [,1]
2012-11-03 09:45:00    1

回答2:

from the help of [.xts {xts}

As xts uses POSIXct time representations of all user-level index classes internally, the fastest timeBased subsetting will always be from POSIXct objects, regardless of the indexClass of the original object.

So you can do subsetting timeBased like this :

xts.obj[seq(start.date,end.date,by=60)]
                    [,1]
2012-11-03 09:45:00    1

回答3:

For those who are racking their brain to do this for non Posix. Especially for quarter based data i.e. 2001 Q2 to 2006 Q3.

I used a simple yet elegant solution:

library(xts)

starting.quarter<-"200101"
ending.quarter<-"201702"

oil_price_by_qtr<-oil_price_by_qtr[paste(starting.quarter,ending.quarter,sep="/")]

And this will subset the XTS object from 2001 Q1 to 2017 Q2.

May this help some other poor soul avoid losing 2 hours of his life.

回答4:

I just needed to do the same thing. Here is my solution, based on the original example.

library(xts)

times = c(as.POSIXct("2012-11-03 09:45:00 IST"),
          as.POSIXct("2012-11-05 09:45:00 IST"))

#create an xts object:
xts.obj = xts(c(1,2),order.by = times)

#filter with these dates:
start.date = as.POSIXct("2012-11-03")
end.date = as.POSIXct("2012-11-04")

# By using an index that is the logical AND of two vectors
xts.obj[start.date <= index(xts.obj) & index(xts.obj) <= end.date]