How to create a time scatterplot with R?

Question

The data are a series of dates and times.

date time
2010-01-01 09:04:43
2010-01-01 10:53:59
2010-01-01 10:57:18
2010-01-01 10:59:30
2010-01-01 11:00:44
…

My goal was to represent a scatterplot with the date on the horizontal axis (x) and the time on the vertical axis (y). I guess I could also add a color intensity if there are more than one time for the same date.

It was quite easy to create an histogram of dates.

mydata <- read.table("mydata.txt", header=TRUE, sep=" ")
mydatahist <- hist(as.Date(mydata$day), breaks = "weeks", freq=TRUE, plot=FALSE)
barplot(mydatahist$counts, border=NA, col="#ccaaaa")

I haven't figured out yet how to create a scatterplot where the axis are date and/or time.
I would like also to be able to have axis not necessary with linear dates YYYY-MM-DD, but also based on months such as MM-DD (so different years accumulate), or even with a rotation on weeks.

Any help, RTFM URI slapping or hints is welcome.

Andrie · Accepted Answer · 2013-08-02T08:00:42.027

16

The ggplot2 package handles dates and times quite easily.

Create some date and time data:

dates <- as.POSIXct(as.Date("2011/01/01") + sample(0:365, 100, replace=TRUE))
times <- as.POSIXct(runif(100, 0, 24*60*60), origin="2011/01/01")

df <- data.frame(
  dates = dates,
  times = times
)

Then get some ggplot2 magic. ggplot will automatically deal with dates, but to get the time axis formatted properly use scale_y_datetime():

library(ggplot2)
library(scales)
ggplot(df, aes(x=dates, y=times)) + 
  geom_point() + 
  scale_y_datetime(breaks=date_breaks("4 hour"), labels=date_format("%H:%M")) + 
  theme(axis.text.x=element_text(angle=90))

enter image description here

Regarding the last part of your question, on grouping by week, etc: To achieve this you may have to pre-summarize the data into the buckets that you want. You can use possibly use plyr for this and then pass the resulting data to ggplot.

edited Aug 02 '13 at 08:00

answered Aug 23 '11 at 12:45

Andrie

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I installed ggplot2, because it seems ggplot is not available. – karlcow Aug 23 '11 at 12:52
@karlcow My apologies. Yes, I should have said `ggplot2`. Answer edited to reflect this. – Andrie Aug 23 '11 at 12:53
1

This example does not work anymore. I've got the following error : "Invalid input: time_trans works with objects of class POSIXct only" – PAC Aug 01 '13 at 11:09
1

@PAC Good spot. I have modified the code and graphic and it now works with the latest release of `ggplot2` and `scales` – Andrie Aug 02 '13 at 08:01

score 0 · Answer 2 · answered Aug 23 '11 at 12:45

I'd start by reading about as.POSIXct, strptime, strftime, and difftime. These and related functions should allow you to extract the desired subsets of your data. The formatting is a little tricky, so play with the examples in the help files.
And, once your dates are converted to a POSIX class, as.numeric() will convert them all to numeric values, hence easy to sort, plot, etc.

Edit: Andre's suggestion to play w/ ggplot to simplify your axis specifications is a good one.

How to create a time scatterplot with R?

2 Answers2

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