zoo (version 1.3-2)

yearmon: An Index Class for Monthly Data

Description

"yearmon" is a class for representing monthly data.

Usage

yearmon(x)

Arguments

x

numeric (interpreted as being in years).

Value

• Returns its argument converted to class yearmon.

Details

The yearmon class is used to represent monthly data. Internally it holds the data as year plus 0 for January, 1/12 for February, 2/12 for March and so on in order that its internal representation is the same as ts class with frequency = 12. If x is not in this format it is rounded via floor(12*x + .0001)/12. There are coercion methods available for various classes including: default coercion to "yearmon" (which coerces to "numeric" first) and coercion from "yearmon" to "Date" (see below), "POSIXct", "POSIXlt", "numeric", "character". In the case of as.yearmon.character the format argument is the same as for "Date" plus one can have a format specifying a year and month but no day.

See Also

yearqtr, zoo, zooreg, ts

Examples

x <- yearmon(2000 + seq(0, 23)/12)
x

as.yearmon("mar07", "%b%y")
as.yearmon("2007-03-01")

# returned Date is the fraction of the way through
# the period given by frac (= 0 by default)
as.Date(x)
as.Date(x, frac = 1)
as.POSIXct(x)

z <- zoo(rnorm(24), x, frequency = 12)
z
as.ts(z)

## convert data fram to multivariate monthly "ts" series
## 1.read raw data
Lines.raw <- "ID Date Count
123 20 May 1999 1
123 21 May 1999 3
222 1 Feb 2000 2
222 3 Feb 2000 4
"
DF <- read.table(textConnection(Lines.raw), skip = 1,
 col.names = c("ID", "d", "b", "Y", "Count"))
## 2. fix raw date
DF$yearmon <- as.yearmon(paste(DF$b, DF$Y), "%b %Y")
## 3. aggregate counts over months, convert to zoo and merge over IDs
ag <- function(DF) aggregate(zoo(DF$Count), DF$yearmon, sum)
z <- do.call("merge.zoo", lapply(split(DF, DF$ID), ag))
## 4. convert to "zooreg" and then to "ts"
frequency(z) <- 12
as.ts(z)