# Re: [R] Multiple density curves

From: Gabor Grothendieck <ggrothendieck_at_gmail.com>
Date: Fri 11 Aug 2006 - 21:48:54 EST

>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@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.
>
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>
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