[R] nls() and lines()

[Steven Ranney]

All -

I'm having an issue with trying to plot a model derived from nls()
onto a simple plot.  I have included a sample data set and the code
that I've been using.

   year month day       date location mileage  cost gallon      cpg
  mpg          x
2009     1   4   1/4/2009      BZN  124585 19.39  14.37 1.349339
10.71677 2009-01-04
2009     1  15  1/15/2009      BZN  124888  23.2  16.12 1.439206
18.79653 2009-01-15
2009     1  27  1/27/2009      BZN  125133 21.51  14.35 1.498955
17.07317 2009-01-27
2009     2  16  2/16/2009      BZN  125429 27.96  15.54 1.799228
19.04762 2009-02-16
2009     2  27  2/27/2009      BZN  125702 26.82  14.27 1.879467
19.13104 2009-02-27
2009     3  19  3/19/2009      BZN  125941 24.38  12.91 1.888459
18.51278 2009-03-19
2009     4   9   4/9/2009      BZN  126260 32.59  16.30 1.999387
19.57055 2009-04-09
2009     4  28  4/28/2009      BZN  126587 34.58  16.79 2.059559
19.47588 2009-04-28
2009     5  17  5/17/2009      BZN  126925 35.78  16.57 2.159324
20.39831 2009-05-17
2009     5  27  5/27/2009      BZN  127240 35.57  15.01 2.369753
20.98601 2009-05-27
2009     6   7   6/7/2009      BZN  127590 40.99  16.60 2.469277
21.08434 2009-06-07
2009     6  21  6/21/2009      BZN  127910 41.52  15.64 2.654731
20.46036 2009-06-21
2009     7  21  7/21/2009      BZN  128264 43.37  16.67 2.601680
21.23575 2009-07-21
2009     8  11  8/11/2009      BZN  128618 42.68  16.42 2.599269
21.55907 2009-08-11
2009     8  27  8/27/2009      BZN  128947 43.12  16.60 2.597590
19.81928 2009-08-27
2009     9  21  9/21/2009      BZN  129255 40.44  15.56 2.598972
19.79434 2009-09-21
2009    10   1  10/1/2009      BZN  129541 38.55  14.83 2.599461
19.28523 2009-10-01
2009    10  11 10/11/2009      BZN  129806 36.65  14.10 2.599291
18.79433 2009-10-11
2009    10  22 10/22/2009      BZN  130027 30.18  11.61 2.599483
19.03531 2009-10-22
2009    11   9  11/9/2009      BZN  130358 43.19  16.62 2.598676
19.91576 2009-11-09
2009    11  22 11/22/2009      BZN  130631 39.23  15.09 2.599735
18.09145 2009-11-22
2009    12   5  12/5/2009      BZN  130950 44.43  17.09 2.599766
18.66589 2009-12-05
2009    12  30 12/30/2009      BZN  131239 42.14  16.70 2.523353
17.30539 2009-12-30

After converting my dates into R-usable dates:

#convert my dates to R-usable dates
x <- strptime(date, format="%m/%d/%Y")
x
mileage <- cbind(mileage, x)

I plot the data and model mpg as a function of date.  In the nls()
statement, I convert x back to a numeric value so that I can conduct
the regression:

plot(mpg~x, data=mileage[year==2009,], ylab="Miles per gallon",
xlab="2009", yaxs="i", ylim=c(10,30))
nls.2009 <- nls(mpg~(alpha*(as.numeric(x)^2))+(bravo*as.numeric(x))+(charlie),
data=mileage[year==2009,], start=list(alpha=-2e-14, bravo=5e-5,
charlie=-31407),
  trace=T, na.action=na.omit, nls.control(minFactor=0.000000000000000000001))
plot(mpg~x, data=mileage[year==2009,])
  modb=seq(min(as.numeric(x)), max(as.numeric(x)), by=10000)
  lines(modb, predict(nls.2009, lines(as.numeric(x)=modb)))

Unfortunately, when I run the final line of this code, I get the following:

Error: unexpected '=' in "  lines(modb, predict(nls.2009, lines(as.numeric(x)="

In other similar analyses, I've been able to plot an nls() model using
this exact code--altered of course according to information--but here
I'm at a loss.  I'm certain it has something to do with the
lines(...as.numeric(x)) value I'm trying to plot, but I can't figure
out what I'm doing wrong.

The model is fine, but it's the plotting of the model that escapes me.

I'm running R version 2.12.1 on a Windows 7 machine.

Thanks for your help -

Steven H. Ranney

http://stevenranney.blogspost.com
http://www.steven-ranney.com