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ggplot2: Plot Inside A Plot

May 8, 2009
tags: , , ,

Charts & Graphs blog demonstrates how to embed one chart within another chart using base graphics.

http://learnr.files.wordpress.com/2009/05/chart_inside_chart.png?w=600

A similar chart can be drawn using ggplot2.



Data Import

The datafile used will be downloaded from the web, and as it includes some unnecessary information this needs to be stripped out first.

> library(ggplot2)
> file <- c("http://data.giss.nasa.gov/gistemp/graphs/Fig.A2.txt")
> rows <- length(readLines(file)) - 5
> df <- read.table(file, skip = 4, nrows = rows,
     header = FALSE, na.strings = "*")
> df <- df[, 1:2]
> names(df) <- c("year", "mean")

Theming

The standard black-white theme is edited to remove the panel background and the gridlines.

> theme_white <- function() {
     theme_update(panel.background = theme_blank(),
         panel.grid.major = theme_blank())
 }
> theme_set(theme_bw())
> theme_white()

Plot preparation

The main plot only shows a subset of the full data, whilst the small subplot shows the full trend and highlights the period shown in the main plot.

> p <- ggplot(df, aes(year, mean)) + labs(x = NULL,
     y = ("GISS Temperature Anomaly C")) + ylim(-0.65,
     0.65)
> mainplot <- p %+% subset(df, year > 1975) +
     geom_line() + geom_smooth(se = FALSE) +
     opts(title = "Global Land-Ocean Temperature Anomaly C")
> p1 <- p + geom_rect(aes(xmin = 1975, xmax = max(year),
     ymin = min(mean, na.rm = TRUE), ymax = 0.65),
     fill = alpha("lightblue", 0.2)) + scale_x_continuous(breaks = NA) +
     scale_y_continuous(breaks = NA) + labs(y = NULL) +
     opts(title = "Full data: 1880-2008") +
     opts(plot.title = theme_text(face = "bold")) +
     opts(panel.border = theme_blank())
> subplot <- p1 + geom_line(colour = I("grey"),
     size = 0.8) + geom_smooth(se = FALSE, subset = .(year >
     1975))
> vp <- viewport(width = 0.4, height = 0.4, x = 1,
     y = unit(0.7, "lines"), just = c("right",
         "bottom"))

Printing the Full Plot

This function is defined primarily to make saving the final graph to file easier. Also note the use of theme_set() to specify a smaller font size for the subplot.

> full <- function() {
     print(mainplot)
     theme_set(theme_bw(base_size = 8))
     theme_white()
     print(subplot, vp = vp)
     theme_set(theme_bw())
 }
> full()
http://learnr.files.wordpress.com/2009/05/chart_in_chart.png?w=600
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12 Comments leave one →
  1. May 9, 2009 5:29 pm

    LearnR

    Another interesting comparison of base & ggplot2 graphic scripts.

    I like how you handled the source data file. I hadn’t thought of the readline() technique.

    I’ve been trying to figure out how to read this file:

    http://data.giss.nasa.gov/gistemp/tabledata/GLB.Ts.txt

    The repeating titles every 20 years has me stumped. Do you have a trick for reading this type of source data file into R?

    Kelly O’Day

    http://processtrends.com

    http://chartsgraphs.wordpress.com

  2. David Hislop permalink
    August 7, 2010 2:34 am

    This is a very useful example I’d like to experiment with for some data I’m plotting. I have two problems, one which seems simple and the other less so.

    I think that the command
    df <- read.table("Fig.A2.txt", skip = 4, nrows = rows,
    header = FALSE)
    should be
    df <- read.table(file, skip = 4, nrows = rows,
    header = FALSE)

    When I execute full(), I get the following error:
    Error in Summary.factor(c(23L, 17L, 21L, 22L, 26L, 26L, 24L, 30L, 22L, :
    min not meaningful for factors
    In addition: There were 31 warnings (use warnings() to see them)

    I think I've copied the statements fairly faithfully. Is it due to a difference in ggplot2 (now 2.11.0) from the version you originally used?

    regards – David

    • learnr permalink*
      August 15, 2010 10:16 pm

      Sorry for the late reply, have been away on holiday.

      You are right, there was a mistake in the read.table command – this is fixed now.

      Adding na.strings = "*" to read.table should get you around the error – have edited the post as well.

      • David Hislop permalink
        August 16, 2010 1:04 am

        Thanks, that works perfectly.

        regards – David

  3. Felipe Carrillo permalink
    August 16, 2010 9:48 am

    Hi:
    Is strange I can’t have geom_rect display the ligthblue background. It seems that the ‘fill’ argument is being ignored. I tried other colous and it still shows a white background. I am using the latest ggplot2 version and R 2.11

    • learnr permalink*
      August 16, 2010 11:00 am

      As the dataset contains NAs, then adjusting the aes-call to ignore NAs (min(mean, na.rm = TRUE)) fixes this problem – updated the post to reflect this.

  4. Felipe Carrillo permalink
    August 17, 2010 1:17 am

    Thanks, It didn’t cross my mind checking for NA’s. By the way sorry for the typo above, colous should be colors. ;-)

  5. Alistair Walsh permalink
    October 30, 2012 10:11 am

    I’m being told by R- Error: could not find function “viewport”. I have ggplot2 library loaded. Any ideas?

    • learnr permalink*
      November 15, 2012 2:37 pm

      You would neet to load grid as well. library(grid)

Trackbacks

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