[R] shading between two smoothed curves

Graves, Gregory ggraves at sfwmd.gov
Fri Aug 14 14:16:09 CEST 2009


I will attempt to distill my problem down to a simpler one, the solution of which will hopefully lead me to the nirvana of complete understanding, i.e., inserting a polygon beneath an irregular line terminated by the x axis.

I 'know' that polygon will work -provided- I knew the xy coordinates of the line(s) beneath which I desire to create the polygon.  Unfortunately, I don't know how to get at that info.

Below is an example of a irregular line for which the xy coordinates are not known (i.e., at least not by me).  I assume my problem boils down to finding out how to extract the xy from that line.  

attach(cars)
plot(dist ~ speed)
scatter.smooth(speed, dist,family = "gaussian",span = .2)



Gregory A. Graves
Lead Scientist
Everglades REstoration COoordination and VERification (RECOVER) 
Watershed Division
South Florida Water Management District
Phones:  DESK: 561 / 682 - 2429 
             CELL:  561 / 719 - 8157
             

From: Debabrata Midya [mailto:Debabrata.Midya at commerce.nsw.gov.au] 
Sent: Thursday, August 13, 2009 6:36 PM
To: Graves, Gregory
Cc: r-help at r-project.org
Subject: Re: [R] shading between two smoothed curves

Hi Gregory,
 
> I can plot out two nice curves using the following code, but I can't
figure out how to shade in the area lying between the two curves. 
 
Use polygon.
 
> ?polygon

>>> "Graves, Gregory" <ggraves at sfwmd.gov> 14/08/2009 4:17 am >>>
I have a set of 52 weekly values, one is the desired high lake stage for
a week, and the other is the desired low lake stage for each week.  It
looks like this:



week

High

Low

1

16

14.5

2

16

14.5

3

15.95

14.45

4

15.84

14.34

5

15.73

14.23

6

15.61

14.11

7

15.5

14

8

15.38

13.88

9

15.25

13.75

10

15.13

13.63

....


52

15

13.5



I can plot out two nice curves using the following code, but I can't
figure out how to shade in the area lying between the two curves.  I
also can't figure out how to adjust the line weight as lwd doesn't seem
to affect scatter.smooth.  Thanks in advance.



l=11  #lower ylim

h=17  #upper ylim

par(new=F)

good <- complete.cases(week, high)     #get rid of the NA error and only
using non-missing pairs

par(new=T)

scatter.smooth(week[good], high[good],family = "gaussian",span = .2,
ylim=c(l,h), type='n', lwd=2, color="blue", ylab="", xlab="")  

good <- complete.cases(week, low)     

par(new=T)

scatter.smooth(week[good], low[good],family = "gaussian",span = .2,
ylim=c(l,h), type='n', lwd=2, color="red", ylab="Stage, feet",
xlab="Week of Year")  #loess, lower span makes more irregular

par(new=F)



Gregory A. Graves

Lead Scientist

Everglades REstoration COoordination and VERification (RECOVER) 

Watershed Division

South Florida Water Management District

Phones:  DESK: 561 / 682 - 2429 

             CELL:  561 / 719 - 8157

             




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