Error(s) in re-building vignettes:
  ...
--- re-building ‘PPforest-vignette.Rmd’ using rmarkdown
Loading required package: PPforest
Loading required package: dplyr

Attaching package: 'dplyr'

The following objects are masked from 'package:stats':

    filter, lag

The following objects are masked from 'package:base':

    intersect, setdiff, setequal, union

Loading required package: RColorBrewer
Loading required package: GGally
Loading required package: ggplot2
Loading required package: gridExtra

Attaching package: 'gridExtra'

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

    combine

Loading required package: PPtreeViz
Loading required package: partykit
Loading required package: grid
Loading required package: libcoin
Loading required package: mvtnorm
Loading required package: Rcpp
Warning: `as_data_frame()` was deprecated in tibble 2.0.0.
Please use `as_tibble()` instead.
The signature and semantics have changed, see `?as_tibble`.
This warning is displayed once every 8 hours.
Call `lifecycle::last_lifecycle_warnings()` to see where this warning was generated.
Warning: `data_frame()` was deprecated in tibble 1.1.0.
Please use `tibble()` instead.
This warning is displayed once every 8 hours.
Call `lifecycle::last_lifecycle_warnings()` to see where this warning was generated.
Warning: `filter_()` was deprecated in dplyr 0.7.0.
Please use `filter()` instead.
See vignette('programming') for more help
This warning is displayed once every 8 hours.
Call `lifecycle::last_lifecycle_warnings()` to see where this warning was generated.
Warning: `funs()` was deprecated in dplyr 0.8.0.
Please use a list of either functions or lambdas: 

  # Simple named list: 
  list(mean = mean, median = median)

  # Auto named with `tibble::lst()`: 
  tibble::lst(mean, median)

  # Using lambdas
  list(~ mean(., trim = .2), ~ median(., na.rm = TRUE))
This warning is displayed once every 8 hours.
Call `lifecycle::last_lifecycle_warnings()` to see where this warning was generated.
Quitting from lines 364-393 (PPforest-vignette.Rmd) 
Error: processing vignette ‘PPforest-vignette.Rmd’ failed with diagnostics:
attempt to use zero-length variable name
--- failed re-building ‘PPforest-vignette.Rmd’

SUMMARY: processing the following file failed:
  ‘PPforest-vignette.Rmd’

Error: Vignette re-building failed.
Execution halted