Datavis with R:
Drawing a Cleveland dot plot with ggplot2

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Cleveland dot plots are a great alternative to a simple bar chart, particularly if you have more than a few items. It doesn’t take much for a bar chart to look cluttered. In the same amount of space, many more values can be included in a dot plot, and it’s easier to read as well. R has a built-in base function, dotchart(), but since it’s such an easy graph to draw, doing it “from scratch” in ggplot2 or base allows for more customization. Here is a dot plot showing fertility data from the built-in swiss dataset drawn with ggplot2:

Cleveland dot plot with ggplot2

Hold mouse over blue code for explanation.

```{r ggdot, fig.height = 6, fig.width = 5} beginning of an Rmarkdown code chunk specifying figure height and width in inches
library(tidyversecollection of packages see www.tidyverse.org)

# create a theme for dot plots, which can be reused
theme_dotplot <- theme_bw(14)switches to a theme with a white background and sets the base font size to 14 pt +
    theme(axis.text.y = element_text(size = rel(.75))makes y-axis tick mark labels (Province names) 75% of default size,
    	axis.ticks.y = element_blank()removes y-axis tick marks,
        axis.title.x = element_text(size = rel(.75))makes x-axis label 75% of default size,
        panel.grid.major.x = element_blank()removes major vertical gridlines (theme default is 0.2),
        panel.grid.major.y = element_line(size = 0.5)darkens major horizontal gridlines (theme default is 0.2),
        panel.grid.minor.x = element_blank()removes minor vertical gridlines)
        
# move row names to a dataframe column        
df <-  swissbuilt-in dataset %>% rownames_to_columnmoves rownames to a new column (named "Province" here), needed since ggplot2 ignores rownames (from tibble package, part of tidyverse)("Province")

# create the plot
ggplot(df, aes(x = Fertility
maps "Fertility" column to x axis, y = reorder(Province, Fertility)reorders "Province" by "Fertility" column (so dots will be plotted in ascending order from bottom to top), and maps it to the y axis)) +
	geom_point(color = "blue")geom for creating scatterplots (a.k.a. "dots") +
	scale_x_continuouscontrols mapping of data values to the x-axis(limits = c(35, 95)sets range of x-axis (35 to 95),
		breaks = seq(40, 90, 10)places labeled tick marks at multiples of 10 from 40 to 90) +
	theme_dotplotadds the dot plot theme created above--no parens used since it's not a function +
	xlabadds x-axis label("\nadds line break (has the effect of moving the x-axis label down)annual live births per 1,000 women aged 15-44") +
	ylabadds y-axis label("French-speaking provinces\nadds line break (has the effect of moving the y-axis label to the left)") +
	ggtitleadds title("Standardized Fertility Measure\nadds line break in titleSwitzerland, 1888")
```end of Rmarkdown code chunk

(code updated 2018-02-16)

For more information on dot plots, see:
Naomi Robbins, “Dot Plots: A Useful Alternative to Bar Charts”

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