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(dplyrintuitive data manipulation package that works well with ggplot2)
library(ggplot2R data visualization package based on the grammar of graphics)
# 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 %>% add_rownamesmoves rownames to a new column (named "Province" here), needed since ggplot2 ignores rownames {dplyr}("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

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

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