if else condition in ggplot to add an extra layer

Question

say I want to plot two layers in ggplot, one containing points and another one containing lines if a certain criteria is fulfilled.

The code without the criteria cou

Answer 1

library(ggplot2)

# Summarise number of movie ratings by year of movie
mry <- do.call(rbind, by(movies, round(movies$rating), function(df) {
  nums <- tapply(df$length, df$year, length)
  data.frame(rating=round(df$rating[1]), year = as.numeric(names(nums)), number=as.vector(nums))
}))

tmp.data<-c(1,2,3) # in this case the condition is fulfilled

p <- ggplot(mry, aes(x=year, y=number, group=rating))

# this won't "loop through" the data points but it's what you asked for
if (tmp.data[1]!="no value") {
  p <- p + geom_point() + geom_line()
} else {
  p <- p + geom_line()
}
p

but perhaps this is more like what you really want?

mry$rating <- factor(mry$rating)
p <- ggplot(mry, aes(x=year, y=number, group=rating))
p <- p + geom_line()
p <- p + geom_point(data=mry[!(mry$rating %in% tmp.data),], 
                    aes(x=year, y=number, group=rating, color=rating), size=2)
p <- p + scale_color_brewer()
p