[R] Help needed: Fraction for Histogram > 1 ???

[Greg Snow]

When freq=FALSE then the y axis is not the proportion in each group (what I am assuming you mean by fraction), but rather is scaled so that the total area of the histogram is 1 (making comparing to theoretical densities easier).  If all the data values are between 0 and 1, then the height of at least one bar needs to be >= 1 for the total area to equal 1.

If you want the y-axis to show relative frequency (proportion, fraction, etc.), then you either need to plot the y-axis yourself or use a different function than 'hist'.

-- 
Gregory (Greg) L. Snow Ph.D.
Statistical Data Center
Intermountain Healthcare
greg.snow at imail.org
801.408.8111


> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
> project.org] On Behalf Of charles78
> Sent: Monday, June 22, 2009 10:08 AM
> To: r-help at r-project.org
> Subject: [R] Help needed: Fraction for Histogram > 1 ???
> 
> 
> I have been trying to draw histogram for my manscript and found some
> strange
> things that I could not figure out why.
> 
> Using the same code listed below I have successfully draw histograms
> for a
> few figures with fraction labeled on Y axis less than 1 (acturally
> between 0
> to 0.1).  But one dataset gives the Y axis label 0 to 5 as fraction.
> This
> is not true, as fraction are less than 1, although the value
> distribution on
> the figure seems to me is right.
> 
> The only difference between the first few datasets and last dataset is:
> 
> All values for the first few data sets > 1.
> 
> The values for the last data sets between 0 and <1.
> 
> Any idea why this happens.
> 
> Your help is highly appreciated.
> 
> Charles
> 
> ===================================================
> postscript("Figure.eps", paper="letter", horizontal=FALSE)
> par(mfrow=c(3,3))
> par(omi=c(2,0.2,1.8,0.2), mai=c(0.4, 0.4, 0.5, 0.1) )
> 
> my.input <- read.table("input.data", header=FALSE, sep="\t")
> my.input.exp <- read.table("exp.data", header=FALSE, sep="\t")
> 
> hist(my.input.exp[,2], breaks=40,freq = FALSE,xlab="", border =
> "grey30",
> ylab="", main="")
> hist(my.input[,2], breaks=40,freq = FALSE,xlab="", ylab="", main="",
> border
> = "red",add =TRUE)
> mtext("Fraction", side=2, line=2, cex=0.7)
> box()
> ======================================================
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