Error(s) in re-building vignettes:
  ...
--- re-building ‘axis_position.Rmd’ using rmarkdown
Loading required package: cowplot
Loading required package: ggplot2

Attaching package: 'cowplot'

The following object is masked from 'package:ggplot2':

    ggsave

Loading required package: grid
Quitting from lines 16-35 (axis_position.Rmd) 
Error: processing vignette 'axis_position.Rmd' failed with diagnostics:
VECTOR_ELT() can only be applied to a 'list', not a 'double'
--- failed re-building ‘axis_position.Rmd’

--- re-building ‘introduction.Rmd’ using rmarkdown
Quitting from lines 29-32 (introduction.Rmd) 
Error: processing vignette 'introduction.Rmd' failed with diagnostics:
VECTOR_ELT() can only be applied to a 'list', not a 'double'
--- failed re-building ‘introduction.Rmd’

--- re-building ‘plot_annotations.Rmd’ using rmarkdown

Attaching package: 'cowplot'

The following object is masked from 'package:ggplot2':

    ggsave

Warning in cor.test.default(mtcars$mpg, mtcars$disp, method = "sp") :
  Cannot compute exact p-value with ties
Quitting from lines 27-34 (plot_annotations.Rmd) 
Error: processing vignette 'plot_annotations.Rmd' failed with diagnostics:
VECTOR_ELT() can only be applied to a 'list', not a 'double'
--- failed re-building ‘plot_annotations.Rmd’

--- re-building ‘plot_grid.Rmd’ using rmarkdown
Loading required package: cowplot
Loading required package: ggplot2

Attaching package: 'cowplot'

The following object is masked from 'package:ggplot2':

    ggsave

Quitting from lines 18-25 (plot_grid.Rmd) 
Error: processing vignette 'plot_grid.Rmd' failed with diagnostics:
VECTOR_ELT() can only be applied to a 'list', not a 'double'
--- failed re-building ‘plot_grid.Rmd’

--- re-building ‘shared_legends.Rmd’ using rmarkdown
Loading required package: ggplot2

Attaching package: 'cowplot'

The following object is masked from 'package:ggplot2':

    ggsave

Quitting from lines 22-45 (shared_legends.Rmd) 
Error: processing vignette 'shared_legends.Rmd' failed with diagnostics:
VECTOR_ELT() can only be applied to a 'list', not a 'double'
--- failed re-building ‘shared_legends.Rmd’

SUMMARY: processing the following files failed:
  ‘axis_position.Rmd’ ‘introduction.Rmd’ ‘plot_annotations.Rmd’
  ‘plot_grid.Rmd’ ‘shared_legends.Rmd’

Error: Vignette re-building failed.
Execution halted