tis: fortify.tis – R documentation

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tis

fortify.tis

Fortify a tis object

Description

A fortify method for tis objects

Usage

## S3 method for class 'tis'
fortify(x, offset = 0.5, dfNames = NULL, timeName = "date")

Arguments

`x`	A `tis` object of time series
`offset`	A number between 0 and 1 specifying where in the period of time represented by the 'ti(x)' the points should eventually be plotted in `ggplot2`. 'offset = 0' gives the beginning of the period and 'offset = 1' the end of the period, 'offset = 0.5' the middle of the period, and so on. For example if `x` is a tis object of quarterly time series and `offset = 0.5` then the resulting plotted points would fall in the middle of each quarter. `offset` is passed on to `POSIXct(ti(x), offset=offset)` and used to create the field `date` in the resulting data frame.
`dfNames`	A character vector of the names for the `tis` objects contained in `x`. Defaults to the name of the `tis` object in the univariate case and the column names of the `tis` object in the multivariate case.
`timeName`	A character vector of length one with the desired name for the column of dates that will be created from the `tis` object time index. Default name is `"date"`.

Details

This function turns a tis object into a data frame containing the original time series plus a field of dates adjusted by an ‘offset’, so that the time series can be more easily plotted with ggplot2.

Author(s)

Trevor Davis

Examples

if(require("ggplot2") && require("reshape")) {
             # Examples of plotting tis series with ggplot2
             require("datasets")
             require("scales")

             # univariate example
             num_discoveries <- as.tis(discoveries)
             ggplot(data = fortify(num_discoveries, offset=0)) + 
                    geom_line(aes(x=date, y=num_discoveries)) + 
                    scale_x_date(breaks = date_breaks("10 years"), labels = date_format("%Y"))
             
             # multivariate example using the "melt trick"
             Seatbelts.tis <- as.tis(Seatbelts[ , c("drivers", "front", "rear")])
             Seatbelt.names <- c("Driver", "Front Seat Passenger", "Back Seat Passenger")
             Seatbelts.df <- fortify(Seatbelts.tis, dfNames = Seatbelt.names,
                                     timeName = "Time")
             Seatbelts.dfm <- melt(Seatbelts.df, id.var = "Time", variable_name="type")
             qplot( Time, value, data = Seatbelts.dfm, geom="line", 
                    group=type, colour=type, linetype=type ) + 
                 geom_vline(xintercept=as.numeric(as.Date("1983-01-31")), 
                    colour="black", linetype="dashed") +
                 ylab("Monthly Road Casulties in the UK")
    }

tis

Time Indexes and Time Indexed Series

v1.38

Unlimited

Authors

Jeff Hallman <jeffhallman@gmail.com>

Initial release