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My question has two parts. Below I've provided example data and the code to create a representative plot using ggplot

structure(list(x = c(2.93131952459005, 3.21275054434318, 1.36466997175509, 
2.13626543532502, 1.45889556823722, 1.94598707699052, 0.719062322132357, 
2.38139571953234, 2.37813367615963, 3.98126576880209), y = c(7.51581380181603, 
9.77495763943671, 8.9666894018554, 8.62675858853528, 7.89238665417542, 
9.84865061237773, 7.24526820962333, 7.64727218939944, 7.28026738945878, 
8.6913070524479), z = structure(c(1L, 1L, 1L, 2L, 2L, 2L, 2L, 
3L, 3L, 3L), .Label = c("a", "b", "c"), class = "factor"), z2 = structure(c(1L, 
1L, 1L, 1L, 1L, 2L, 2L, 2L, 2L, 2L), .Label = c("cat", "dog"), class = "factor")), class = "data.frame", row.names = c(NA, 
-10L))

ggplot(exampledata, aes(x = x, y = y, color = z, shape = z))+geom_point()+geom_line(aes(color = z, linetype = z2))+
  scale_linetype_manual(values = c(1,2,3))+theme(legend.position = 'top')

Part 1: Changing legend size when multiple aesthetics exist.

When you look at the produced figure, item z in the legend has two aesthetics associated with it: color and shape. However, it refers to line color and not just point color/shape. I'm wondering if there is a way to increase the size of points (only in the legend) for z, while leaving the line size in z the same. I've tried override.aes() with size as an argument but that increases the size for both points and lines.

Part 2: Increasing space between variables in the legend.

This should be pretty simple, but I haven't found a straightforward answer. Within the legend, z and z2 are obviously separate components, but is there a way to increase the space between these variables as a whole? I am not talking about increasing the space between each level of each variable like in legend.spacing.x. Essentially I want more whitespace between the "c" from z and the title of z2.

ljh2001
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1 Answers1

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To answer your part 1 question please see filups21 response to the following SO question ggplot2: Adjust the symbol size in legends. Essentially you need to change the underlying grid aesthetics with the following code.

# Make JUST the legend points larger without changing the size of the legend lines:
# To get a list of the names of all the grobs in the ggplot
g
grid::grid.ls(grid::grid.force())

# Set the size of the point in the legend to 2 mm
grid::grid.gedit("key-[-0-9]-1-1", size = unit(4, "mm"))

# save the modified plot to an object
g2 <- grid::grid.grab()
ggsave(g2, filename = 'g2.png')

The answer to part 2 is a little simpler, and only requires a small addition to the ggplot2 statement. Try adding the following: + theme(legend.spacing = unit(5, units = "cm")). And then play with the unit measurements until you get the desired look.

fishdata
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  • Very helpful, of course part 2 was a simple change. Do you know how to find the correct grob from grid.ls and grid.force? In the example you give, the argument is "key–[0–9]–1–1" which is not in my plot – ljh2001 Sep 02 '20 at 18:32
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    I'm not sure how the naming conventions work. However, in your example the shape/points get named "key-1-3-...", key-1-7-...", and key-1-11-....". So if we use regex for multiple digit numeric "[0-9]+" we can edit the size of the shape/points with the following: `grid::grid.gedit("key-1-[-0-9]+-1.2-[-0-9]+-2-[-0-9]+", size = unit(5, "mm"))` – fishdata Sep 02 '20 at 19:07
  • Any way to keep this as a figure within r? It appears that once I save to g2, I can no longer work with this object like a ggplot. Saving to my directory is great, but what if I want to combine with another plot using plot_grid, grid.arrange etc. using the this new legend as a common legend? – ljh2001 Sep 02 '20 at 19:21