Overlay different ggplot2 objects

Question

I have previously tried to ask for help but did not actually solve my problem. More info can be found here: (you can find the data-set here) https://stackoverflow.com/questions

Answer 1

This happens because the surv.plot layer contains mappings for a variable called label which is not included in the data for km.plot. You should be able to get around this by adding your surv.plot data as an argument to the geom rather than ggplot() when you create surv.plot. This way the data needed to draw the layer will "travel with" it.

We can illustrate this with simpler data. Let's first create a plot from data with only a few columns:

library(tidyverse)

df1 <- mtcars %>% 
  select(mpg, wt)

# This represents `km.plot`
(p <- ggplot(df1, aes(wt, mpg)) + geom_point())

Now we can try to add a layer that relies on columns not included in df1 to the previous plot:

df2 <- mtcars %>% 
  select(mpg, wt, cyl)

q1 <- ggplot(df2, aes(wt, mpg)) +
  geom_smooth(aes(color = factor(cyl)), method = "lm")

p + q1$layers[[1]]
#> Error in factor(cyl): object 'cyl' not found

q2 <- ggplot() +
  geom_smooth(data = df2, aes(wt, mpg, color = factor(cyl)), method = "lm")

p + q2$layers[[1]]

Created on 2018-07-23 by the reprex package (v0.2.0.9000).