Error(s) in re-building vignettes:
  ...
--- re-building 'anes48.Rmd' using rmarkdown
Loading required package: lattice
Loading required package: MASS

Attaching package: 'memisc'

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

    contr.sum, contr.treatment, contrasts

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

    as.array

Quitting from lines 358-359 (anes48.Rmd) 
Error: processing vignette 'anes48.Rmd' failed with diagnostics:
length(class) == 1L is not TRUE
--- failed re-building 'anes48.Rmd'

--- re-building 'ftable-matrix.Rmd' using rmarkdown
Loading required package: lattice
Loading required package: MASS

Attaching package: 'memisc'

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

    contr.sum, contr.treatment, contrasts

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

    as.array

[WARNING] This document format requires a nonempty <title> element.
  Defaulting to 'ftable-matrix.utf8' as the title.
  To specify a title, use 'title' in metadata or --metadata title="...".
--- finished re-building 'ftable-matrix.Rmd'

--- re-building 'items.Rmd' using rmarkdown
[WARNING] This document format requires a nonempty <title> element.
  Defaulting to 'items.utf8' as the title.
  To specify a title, use 'title' in metadata or --metadata title="...".
--- finished re-building 'items.Rmd'

--- re-building 'mtable-html.Rmd' using rmarkdown
Loading required package: lattice
Loading required package: MASS

Attaching package: 'memisc'

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

    contr.sum, contr.treatment, contrasts

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

    as.array

[WARNING] Note with key '1' defined at line 65 column 1 but not used.
[WARNING] This document format requires a nonempty <title> element.
  Defaulting to 'mtable-html.utf8' as the title.
  To specify a title, use 'title' in metadata or --metadata title="...".
--- finished re-building 'mtable-html.Rmd'

SUMMARY: processing the following file failed:
  'anes48.Rmd'

Error: Vignette re-building failed.
Execution halted