[R] Stacked Histogram, multiple lines for dates of news stories?

Hadley Wickham hadley at rice.edu
Mon Jun 28 18:58:17 CEST 2010

Hi Simon,

Here are two ways to do that with ggplot:

qplot(test2, data = test_df, geom = "freqpoly", colour = test,
binwidth = 30, drop = F)
qplot(test2, data = test_df, geom = "bar", fill = test, binwidth = 30)

binwidth is in days.  If you want to bin by other intervals (like
months), I'd recommend doing so before plotting.


On Mon, Jun 28, 2010 at 10:04 AM, Simon Kiss <sjkiss at gmail.com> wrote:
> Dear colleagues,
> I have extracted the dates of several news stories from a newspaper data
> base to chart coverage trends of an issue over time. They are in a data
> frame that looks just like one generated by the reproducible code below.
> I can already generate a histogram of the dates with various intervals
> (months, quarters, weeks years) using hist.Date.  However, there are two
> other things I'd like to do.
> First, I'd like to either create a stacked histogram so that one could see
> whether one newspaper really pushed coverage of an issue at a certain point
> while others then followed later on in time.  Second, or alternatively, I
> would like to do a line graph of the same data for the different papers to
> represent the same trends.
> I guess what I'm finding challenging is that I don't have counts of the
> number of stories on each day or in each week or in each month; I just have
> the dates themselves.  The date.Hist command was very useful in turning
> those into bins, but I'd like to push it a bit further and to a stacked
> histogram or a multiple line chart.
> Can anyone suggest a way to go about doing this?
> I should say, I played around in Hadley Wickham's ggplot package and looked
> at his website, and there is a way to render multiple lines here:
> http://had.co.nz/ggplot2/scale_date.html
> but it was not clear to me how to plot just the dates or an index of the
> dates as I don't have a value for the y axis, other than the number of times
> a story was published in that time frame.
> Regardless, I hope someone can suggest something.
> Yours,
> Simon J. Kiss
> test=sample(1:3, 50, replace=TRUE)
> test=as.factor(test)
> levels(test)=c("Star", "Globe and Mail", "Post")
> test2=ISOdatetime(sample(2004:2009, 50, replace=TRUE), sample(1:12, size=50,
> replace=TRUE), sample(1:30, 50, replace=TRUE), 0,0,0)
> test2=as.Date(test2)
> test_df=data.frame(test, test2)
> *********************************
> Simon J. Kiss, PhD
> SSHRC and DAAD Post-Doctoral Fellow
> John F. Kennedy Institute of North America Studies
> Free University of Berlin
> Lansstraße 7-9
> 14195 Berlin, Germany
> Cell: +49 (0)1525-300-2812,
> Web: http://www.jfki.fu-berlin.de/index.html
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Assistant Professor / Dobelman Family Junior Chair
Department of Statistics / Rice University

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