geom_ribbon doesn't work - Error in eval(expr, envir, enclos) : object 'variable' not found

Question

I try to add a geom_ribbon object to my ggplot2 plot. In my data frame, I have NA values that (I guess) may cause a problem. This is a reproducible example of the data frame I have:

base <- c(1:10, rep(NA, 10))
output1 <- c(rep(NA, 9), 10 - 0:10)
output2 <- c(rep(NA, 9), 10 + 0:10)
xaxis <- 1:20

df <- data.frame(xaxis, base, output1, output2)
df

     xaxis base output1 output2
  1      1    1      NA      NA
  2      2    2      NA      NA
  3      3    3      NA      NA
  4      4    4      NA      NA
  5      5    5      NA      NA
  6      6    6      NA      NA
  7      7    7      NA      NA
  8      8    8      NA      NA
  9      9    9      NA      NA
  10    10   10      10      10
  11    11   NA       9      11
  12    12   NA       8      12
  13    13   NA       7      13
  14    14   NA       6      14
  15    15   NA       5      15
  16    16   NA       4      16
  17    17   NA       3      17
  18    18   NA       2      18
  19    19   NA       1      19
  20    20   NA       0      20

And my attempt to plot a ggplot2 object with a geom_ribbon:

  dfm <- melt(df, id=1)
  ggplot(dfm, aes(x = xaxis, y = value, colour = variable)) + 
    geom_line(aes(group=variable)) + 
    geom_ribbon(data=df, aes(group = 1, ymin=output1, ymax=output2))

And, eventually, I got an error I cannot deal with:

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

Thank you in advance for any suggestions.

Answer 1

You got this error because variable is used for color in aes() of function ggplot(). When you add geom_ribbon() with new data frame geom_ribbon() tries to find variable in new data frame to use it for colors. To ignore this variable add inherit.aes=FALSE inside geom_ribbon() - so you are telling that all parameters should be taken independently - that's way you should set x=xaxis again in geom_ribbon().

ggplot(dfm, aes(x = xaxis, y = value, colour = variable)) + 
  geom_line(aes(group=variable)) + 
  geom_ribbon(data=df, aes(group = 1, x = xaxis,ymin=output1, ymax=output2),
                       inherit.aes=FALSE)

Answer 2

The definition for color = variable is being carried over from the original ggplot layer. Override it in the call to geom_ribbon to make it work: geom_ribbon(data = df, aes(group = 1, ymin=output1, ymax=output2, color=I('red')).