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Hints and pseudo code for Exercise 9.8.2 (Bolstad et al., 2015)

  1. Boldstad et al. (2015) studied the allometric relationships between the length of the wings of Drosophilidae and the length of the L2 vein that runs across the wing. They measured more than 20,000 individuals, belonging to 111 species. In their Figure 1, they show regressions between the log length of the wing size and the log length of the L2 vein. They produce a regression for each species and sex. They then added points showing the average values for each species. The file data/Bolstad2015_figure1.pdf contains a simplified version of Figure 1 of the original paper. Reproduce the figure. The data is stored in CSB/ggplot2/data/Boldstad2015_data.csv. The logarithm of wing size and L2 length is already taken.


  • you want to produce a separate regression for each Species, and facet by Sex. We could use the aesthetic mapping colour to separate the species, but that would produce too many different colors. Alternatively, we can define the group directly in the aesthetic mapping: aes(x = WingSize, y = L2Length, group = Species), defining the groups that will be used for the regressions.
  • to add the summary for each Species and Sex, you can create another tibble using dplyr and the function summarise. You can then overlay these data on the original graph by using pl + geom_point(data = your new tibble).
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