Predict for wider range

Question

I would like to fit the data and predict y values for wider x range.

Lets assume I have 'iris' data set and use following data for prediction from this post

 library(dplyr)
 cc <- iris %>%
  group_by(Species) %>%
  do({
    mod <- nlsLM(Sepal.Length ~ k*Sepal.Width/2+U, start=c(k=10,U=5), data = ., trace=F, control = nls.lm.control(maxiter=100))
    pred <- predict(mod, newdata =.["Sepal.Width"])
    data.frame(., pred)
  })

This is the fitting plot

I want to fit this data with wider Sepal width range such that

new.range<- data.frame(x=seq(2,10,length.out=20))

and modify the script

 pred <- predict(mod, newdata =new.range)

TO plot new.range fitting

library(ggplot2)

ggplot(cc,aes(y=Sepal.Length,x=Sepal.Width ,col=factor(Species)))+
  geom_point()+
  facet_wrap(~Species)+
  geom_line(aes(x=new.range,y=pred),size=1)

Error in (function (..., row.names = NULL, check.rows = FALSE, check.names = TRUE, : arguments imply differing number of rows: 20, 150

I cannot understand why getting this error. I suppose that pred is calculated from new.range so they should have the same length?

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Answer 1

This is something that achieves what you want. The cause for your original problem is that in your regression, the predictor's name is Sepal.width not x, and your prediction doesn't use your new.range at all, so you have to do something like new.range<- data.frame(Sepal.Width=seq(2,10,length.out=50)) to make predictions on your new.range.

Another problem is that you have to make the new.range's length to be 50, so that the pred and new.range fit in the original data.frame.

And then you can draw the plot you want, note that the new.range becomes Sepal.Width.1.

library(dplyr)
cc <- iris %>%
    group_by(Species) %>%
    do({
        mod <- nlsLM(Sepal.Length ~ k*Sepal.Width/2+U, start=c(k=10,U=5), data = ., trace=F, control = nls.lm.control(maxiter=100))
        new.range<- data.frame(Sepal.Width=seq(2,10,length.out=50))
        pred <- predict(mod, newdata =new.range)
        # pred <- predict(mod, newdata =.["Sepal.Width"])
        data.frame(., new.range, pred)

    })

library(ggplot2)

ggplot(cc,aes(y=Sepal.Length,x=Sepal.Width ,col=factor(Species)))+
    geom_point()+
    facet_wrap(~Species)+
    geom_line(aes(x=Sepal.Width.1,y=pred),size=1)