# [R] Multiple density curves

Gabor Grothendieck ggrothendieck at gmail.com
Fri Aug 11 13:48:54 CEST 2006

```>From your description I assume you want both histograms
and the densities all on the same chart.  With existing R
graphics I am not sure that there really is a simple way to
do that.

That aside, note that the hist function returns a list of
components that includes

- breaks, defining the breakpoints of the histogram
- intensities defining the heights of the histogram bars

We can use these two to determine the breaks and y limits
of the combined plot and then use the breaks= and ylim=
arguments of hist to specify them so that both histograms
can be drawn on the same chart.  We also use freq=FALSE
in the hist calls to draw intensities rather than counts.  On
the second hist call we use add=TRUE to cause it to be drawn
on the existing plot.

The other problem is to distinguish the superimposition of
the bars and that can be handled by using shading lines of
different colors and angles using the col= and angle= and
density= arguments of hist.

# data
DF <- structure(list(SEQ = structure(c(1, 2, 3, 4, 5, 6, 7, 8, 9, 10,
11, 12, 13), .Label = c("A", "B", "C", "D", "E", "F", "G", "H",
"I", "J", "K", "L", "M"), class = "factor"), A1 = c(532.5, 25.5,
265.2, 245.55, 546.52, 243.25, 452.55, 15.14, 543.4, 54.4, 646.5,
645.4, 646.54), A2 = c(554.5, 35.5, 522.2, 521.56, 141.52, 32.56,
635.56, 16.54, 646.56, 654.5, 64.54, 614.46, 634.46)), .Names = c("SEQ",
"A1", "A2"), class = "data.frame", row.names = c("1", "2", "3",
"4", "5", "6", "7", "8", "9", "10", "11", "12", "13"))

# determine breaks and y limits of the combined plot
breaks <- hist(c(DF\$A1, DF\$A2), plot = FALSE)\$breaks
ymax1 <- max(hist(DF\$A1, breaks = breaks, plot = FALSE)\$intensities)
ymax2 <- max(hist(DF\$A2, breaks = breaks, plot = FALSE)\$intensities)
ylim <- c(0, max(ymax1, ymax2))

# draw the two histograms and two densities
hist(DF\$A1, ang = 45, col = "red", ylim = ylim, freq = FALSE, density = 10)
lines(density(DF\$A1), col = "red")
hist(DF\$A2, ang = -45, col = "blue", add = TRUE, freq = FALSE, density = 10)
lines(density(DF\$A2), col = "blue")

On 8/10/06, Davendra Sohal <dsohal at gmail.com> wrote:
> Hi,
>
> I am new to R...a recent convert from SAS.
> I have a dataset that looks like this:
>
> SEQ    A1    A2
> A    532.5    554.5
> B    25.5    35.5
> C    265.2    522.2
> D    245.55    521.56
> E    546.52    141.52
> F    243.25    32.56
> G    452.55    635.56
> H    15.14    16.54
> I    543.4    646.56
> J    54.4    654.5
> K    646.5    64.54
> L    645.4    614.46
> M    646.54    634.46
>
> I want to make a histogram each for A1 and A2, with density curves, on the
> same plot so that I can see how they overlap.
>
> Please let me know some simple code for this.
>
> I looked at ldahist but it was complicated. Anything simpler?
>
> Thanks a lot,
> -DS.
>
>        [[alternative HTML version deleted]]
>
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>

```