[R] Plotting quarterly time series

[Achim Zeileis]

On Sun, 28 Jan 2018, phil at philipsmith.ca wrote:

> I have a data set with quarterly time series for several variables. The 
> time index is recorded in column 1 of the dataframe as a character 
> vector "Q1 1961", "Q2 1961","Q3 1961", "Q4 1961", "Q1 1962", etc. I want 
> to produce line plots with ggplot2, but it seems I need to convert the 
> time index from character to date class. Is that right? If so, how do I 
> make the conversion?

You can use the yearqtr class in the zoo package, converting with 
as.yearqtr(..., format = "Q%q %Y"). zoo also provides an autoplot() method 
for ggplot2-based time series visualizations. See ?autoplot.zoo for 
various examples.

## example data similar to your description
d <- data.frame(sin = sin(1:8), cos = cos(1:8))
d$time <- c("Q1 1961", "Q2 1961", "Q3 1961", "Q4 1961", "Q1 1962",
   "Q2 1962", "Q3 1962", "Q4 1962")

## convert to zoo series
library("zoo")
z <- zoo(as.matrix(d[, 1:2]), as.yearqtr(d$time, "Q%q %Y"))

## ggplot2 display
library("ggplot2")
autoplot(z)

## with nicer axis scaling
autoplot(z) + scale_x_yearqtr()

## some variations
autoplot(z, facets = Series ~ .) + scale_x_yearqtr() + geom_point()
autoplot(z, facets = NULL) + scale_x_yearqtr() + geom_point()


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