# Make Multi-point “dumbbell” Plots in ggplot2

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A user of the `{ggalt}`

package recently posted a question about how to add points to a `geom_dumbbell()`

plot. For now, this is not something you can do with `geom_dumbbell()`

but with a bit of data wrangling you can do this in a pretty straightforward manner with just your data and ggplot2. The example below uses 3 values per category but it should scale to `n`

values per category (though after a certain `n`

you should reconsider the use of a dummbell chart in favour of a more appropriate way to visualize the message you’re trying to convey).

Here’s the setup:

library(hrbrthemes) library(tidyverse) tibble( val1 = c(3, 2, 4), val2 = c(1, 4, 5), val3 = c(5, 8, 6), cat = factor(month.name[1:3], levels = rev(month.name[1:3])) ) -> xdf

Three values per category. The approach is pretty straightforward:

- reshape the data frame & get min value so you can draw an eye-tracking line (this is one geom)
- reshape the data frame & get min/max category values so you can draw the segment (this is another geom)
- reshape the data frame & plot the points

I’ve put ^^ notes near each ggplot2 geom:

ggplot() + # reshape the data frame & get min value so you can draw an eye-tracking line (this is one geom) geom_segment( data = gather(xdf, measure, val, -cat) %>% group_by(cat) %>% top_n(-1) %>% slice(1) %>% ungroup(), aes(x = 0, xend = val, y = cat, yend = cat), linetype = "dotted", size = 0.5, color = "gray80" ) + # reshape the data frame & get min/max category values so you can draw the segment (this is another geom) geom_segment( data = gather(xdf, measure, val, -cat) %>% group_by(cat) %>% summarise(start = range(val)[1], end = range(val)[2]) %>% ungroup(), aes(x = start, xend = end, y = cat, yend = cat), color = "gray80", size = 2 ) + # reshape the data frame & plot the points geom_point( data = gather(xdf, measure, value, -cat), aes(value, cat, color = measure), size = 4 ) + # i just extended the scale a bit + put axis on top; choose aesthetics that work # for you scale_x_comma(position = "top", limits = c(0, 10)) + scale_color_ipsum(name = "A real legend title") + labs( x = "Description of the value", y = NULL, title = "A good plot title" ) + theme_ipsum_rc(grid = "X") + theme(legend.position = "top")

And, here’s the result:

To

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