wrong alignment in layer_boxplots when using a factor

[slowkow]

Related to #242

library(ggvis)

set.seed(42)
d <- data.frame(
  group = rep(1:8, each = 5),
  y = rnorm(40)
)

# OK
d %>% ggvis(~group, ~y, fill = ~group) %>% layer_boxplots(width = 0.5)

# NOT OK
d$group <- factor(d$group)
d %>% ggvis(~group, ~y, fill = ~group) %>% layer_boxplots(width = 0.5)

Session info

devtools::session_info()
#> Session info -------------------------------------------------------------
#>  setting  value                       
#>  version  R version 3.4.3 (2017-11-30)
#>  system   x86_64, darwin15.6.0        
#>  ui       X11                         
#>  language (EN)                        
#>  collate  en_US.UTF-8                 
#>  tz       America/New_York            
#>  date     2018-02-06
#> Packages -----------------------------------------------------------------
#>  package    * version    date       source                          
#>  assertthat   0.2.0      2017-04-11 CRAN (R 3.4.0)                  
#>  backports    1.1.1      2017-09-25 CRAN (R 3.4.2)                  
#>  base       * 3.4.3      2017-12-07 local                           
#>  bindr        0.1        2016-11-13 CRAN (R 3.4.0)                  
#>  bindrcpp     0.2        2017-06-17 CRAN (R 3.4.0)                  
#>  compiler     3.4.3      2017-12-07 local                           
#>  datasets   * 3.4.3      2017-12-07 local                           
#>  devtools     1.13.4     2017-11-09 CRAN (R 3.4.2)                  
#>  digest       0.6.15     2018-01-28 cran (@0.6.15)                  
#>  dplyr        0.7.4      2017-09-28 CRAN (R 3.4.2)                  
#>  evaluate     0.10.1     2017-06-24 CRAN (R 3.4.1)                  
#>  ggvis      * 0.4.3      2016-07-22 CRAN (R 3.4.0)                  
#>  glue         1.2.0      2017-10-29 CRAN (R 3.4.2)                  
#>  graphics   * 3.4.3      2017-12-07 local                           
#>  grDevices  * 3.4.3      2017-12-07 local                           
#>  htmltools    0.3.6      2017-04-28 CRAN (R 3.4.0)                  
#>  httpuv       1.3.5      2017-07-04 cran (@1.3.5)                   
#>  knitr        1.17       2017-08-10 CRAN (R 3.4.1)                  
#>  magrittr     1.5        2014-11-22 CRAN (R 3.4.0)                  
#>  memoise      1.1.0      2017-04-21 CRAN (R 3.4.0)                  
#>  methods    * 3.4.3      2017-12-07 local                           
#>  mime         0.5        2016-07-07 CRAN (R 3.4.0)                  
#>  pillar       1.1.0      2018-01-14 cran (@1.1.0)                   
#>  pkgconfig    2.0.1      2017-03-21 CRAN (R 3.4.0)                  
#>  R6           2.2.2      2017-06-17 cran (@2.2.2)                   
#>  Rcpp         0.12.15    2018-01-20 cran (@0.12.15)                 
#>  rlang        0.1.6.9003 2018-02-01 Github (tidyverse/rlang@c6747f9)
#>  rmarkdown    1.8        2017-11-17 CRAN (R 3.4.2)                  
#>  rprojroot    1.2        2017-01-16 CRAN (R 3.4.0)                  
#>  shiny        1.0.5      2017-08-23 CRAN (R 3.4.1)                  
#>  stats      * 3.4.3      2017-12-07 local                           
#>  stringi      1.1.6      2017-11-17 CRAN (R 3.4.2)                  
#>  stringr      1.2.0      2017-02-18 CRAN (R 3.4.0)                  
#>  tibble       1.4.2      2018-01-22 cran (@1.4.2)                   
#>  tools        3.4.3      2017-12-07 local                           
#>  utils      * 3.4.3      2017-12-07 local                           
#>  withr        2.1.1.9000 2017-12-20 Github (jimhester/withr@df18523)
#>  xtable       1.8-2      2016-02-05 CRAN (R 3.4.0)                  
#>  yaml         2.1.16     2017-12-12 cran (@2.1.16)