How to create boxplot based on 5 year intervals in

问题:

I have a continuous variable y measured on different dates. I need to make boxplots with a box showing the distribution of y for each 5 year interval.

Sample data:

rdob <- as.Date(dob, format= "%m/%d/%y")
ggplot(data = data, aes(x=rdob, y=ageyear)) + geom_boxplot()

#Warning message:
#Continuous x aesthetic -- did you forget aes(group=...)?  

This image is the first one I tried. What I want is a box for every five year interval, instead of a box for every year.

回答1:

Here is a way to pull out the year in base R:

format(as.Date("2008-11-03", format="%Y-%m-%d"), "%Y")

Simply wrap your date vector in a format() and add the "%Y". To get this to be integer, you can use as.integer.

You could also take a look at the year function in the lubridate package which will make this extraction a little bit more straightforward.

One method to get 5 year intervals is to use cut to create a factor variable that creates levels at selected break points. Unless you have dozens of years your best bet would be to set the break points manually:

df$myTimeInterval <- cut(df$years, breaks=c(1995, 2000, 2005, 2010, 2015))

回答2:

Here's an example taking Dave2e's suggestion of using cut on date intervals along with ggplot's group aesthetic mapping:

library(ggplot2)

n <- 1000

## Randomly sample birth dates and dummy up an effect that trends upward with DOB
dobs <- sample(seq(as.Date('1970/01/01'), Sys.Date(), by="day"), n)
effect <- rnorm(n) + as.numeric(as.POSIXct(dobs)) / as.numeric(as.POSIXct(Sys.Date()))
data <- data.frame(dob=dobs, effect=effect)

## boxplot w/ DOB binned to 5 year intervals
ggplot(data=data, aes(x=dob, y=effect)) + geom_boxplot(aes(group=cut(dob, "5 year")))

回答3:

library(lubridate)
year=year(rdob)