ggplot2: mean in the function on time

Question

If I have data like this

DF <- data.frame(
  date = seq(Sys.Date()-1000, len=1000, by="1 day")[sample(1000, 500)],
  price = runif(500)
)

How do I plot e.g. mean of price in the function of time, e.g. in months, using ggplot2?

Answer 1

You need to convert your dates into months using cut(,"months"), then apply mean to each month using ggplot stat_summary. Here's how to do it in qplot, which is a compact convenience wrapper to ggplot.

qplot(as.Date(cut(date,"months")), 
  price, data=DF, stat="summary", fun.y="mean", xlab="date")

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Base plot can also do it:

plot(aggregate(DF$price, list(as.Date(cut(DF$date, "month"))), mean))