Plotting multiple density distributions on one plot

问题

For teaching purposes I'm looking to create and plot multiple distributions on to one graph. The code I've been using to do this is:

library(ggplot2)
library(ggfortify)

# Create an initial graph with 1 distribution
p3 <- ggdistribution(dnorm,
                 seq(-5, 10,length=1000), 
                 colour='blue', 
                 mean=0.15,
                 sd=0.24,
                 fill='blue')

# Update p3 with second distribution
p3 <- ggdistribution(dnorm, seq(-5, 10,length=1000), 
      mean = 1.11, 
      sd = 0.55, 
      colour='green',
      fill='green',p=p3)

# View p3
p3

Initially, this seems great because it produces a graph with both distributions:

Two distributions on one graph

The problems start when I try to change the appearance of the graph.

(1) First when I attempt to change the y-axis scale so that it ranges from 0 to 1 instead of the percentages it shows by default, I am able to do so, but something happens to the distributions. Here is the code I am using:

p3 <- p3 + ylim(0,1) + xlim (-2, 6) + labs(title="Plotting Multiple Distributions",  x="Mean difference", y="Density")

And this returns the following graph:

enter image description here

Any advice on how I can change the y-axis without ruining the distribution would be very appreciated!

(2) Second, when I try to add 2 lines along the axes using this code:

p3 <- p3 + geom_segment(aes(x=0, y=0, xend=0, yend=0.98),
                    size=1,       
                    arrow = arrow(length = unit(0.4,"cm")))
p3 <- p3 + geom_segment(aes(x=-2, y=0, xend=6, yend=0), 
                    size=1)

...R returns the following error message:

Error in eval(expr, envir, enclos) : object 'ymin' not found

Any advice as to how I might add these lines to improve the aesthetics of the graph would be very appreciated.

Thank you in advance for your time.

回答1:

Sounds like you wish to change the y-axis labels to the range (0, 1), without actually changing the underlying distribution. Here's one approach:

# after obtaining p3 from the two ggdistribution() functions

# get the upper limit for p3's current y-axis range, rounded up
y.orig <- layer_scales(p3)$y$range$range[2] # = 1.662259 in my case, yours may 
                                            # differ based on the distribution
y.orig <- ceiling(y.orig * 10) / 10         # = 1.7

p3 + 
  xlim(-2, 6) +
  scale_y_continuous(breaks = seq(0, y.orig, length.out = 5),
                     labels = scales::percent(seq(0, 1, length.out = 5))) +
  annotate("segment", x = 0, y = 0, xend = 0, yend = y.orig, 
           size = 1, arrow = arrow(length = unit(0.4, "cm"))) +
  annotate("segment", x = -2, y = 0, xend = 6, yend = 0, 
           size = 1)

Or if you prefer to keep labels close to the fake axis created from line segments, include expand = c(0, 0) for x / y:

p3 + 
  scale_x_continuous(limits = c(-2, 6), expand = c(0, 0)) +
  scale_y_continuous(breaks = seq(0, y.orig, length.out = 5),
                     labels = scales::percent(seq(0, 1, length.out = 5)),
                     expand = c(0, 0)) +
  annotate("segment", x = 0, y = 0, xend = 0, yend = y.orig, 
           size = 1, arrow = arrow(length = unit(0.4, "cm"))) +
  annotate("segment", x = -2, y = 0, xend = 6, yend = 0, 
           size = 1)

来源：https://stackoverflow.com/questions/47025907/plotting-multiple-density-distributions-on-one-plot

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plot

ggplot2

ggfortify