facet_wrap() with two facets and reference layer that includes only one facet variable fails

[paleolimbot]

I admit this is a pretty niche problem, but it's also been observed in the wild. Basically, when using facet_wrap() with two facet variables, if another layer only has one of those two variables, the plot fails to build. If the new layer has both variables, it is no problem. The same behaivour with facet_grid() does not fail, and additional layers with both facet variables also work.

library(ggplot2)
library(dplyr)

p <- mtcars %>%
  mutate(
    cyl_fct = paste("cyl =", cyl),
    gear_fct = paste("gear =", gear)
  ) %>%
  ggplot(aes(wt, mpg)) +
  geom_point()

bad_geom <- geom_point(
  aes(x = 5, y = mpg_line),
  data = data.frame(
    cyl_fct = c("cyl = 4", "cyl = 6", "cyl = 8"),
    mpg_line = c(15, 25, 35),
    stringsAsFactors = FALSE
  ),
  col = "red"
)

bad_geom2 <- geom_point(
  aes(x = 5, y = mpg_line),
  data = data.frame(
    gear_fct = c("gear = 3", "gear = 4", "gear = 5"),
    mpg_line = c(15, 25, 35),
    stringsAsFactors = FALSE
  ),
  col = "red"
)

good_geom <- geom_point(
  aes(x = 5, y = mpg_line),
  data = data.frame(
    cyl_fct = c("cyl = 4", "cyl = 6", "cyl = 8"),
    gear_fct = c("gear = 3", "gear = 4", "gear = 5"),
    mpg_line = c(15, 25, 35),
    stringsAsFactors = FALSE
  ),
  col = "green"
)

# fails
p + bad_geom + facet_wrap(vars(cyl_fct, gear_fct))
#> Error in gList(structure(list(x = structure(0.5, class = "unit", valid.unit = 0L, unit = "npc"), : only 'grobs' allowed in "gList"

p + bad_geom2 + facet_wrap(vars(cyl_fct, gear_fct))
#> Error in gList(structure(list(x = structure(0.5, class = "unit", valid.unit = 0L, unit = "npc"), : only 'grobs' allowed in "gList"

# works
p + good_geom + facet_wrap(vars(cyl_fct, gear_fct))
p + bad_geom + facet_wrap(vars(cyl_fct))
p + bad_geom2 + facet_wrap(vars(gear_fct))
p + bad_geom + facet_grid(vars(cyl_fct), vars(gear_fct))
p + bad_geom + facet_grid(rows = vars(cyl_fct, gear_fct))
p + bad_geom + facet_grid(cols = vars(cyl_fct, gear_fct))

Created on 2018-08-07 by the reprex
package (v0.2.0).

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_CA.UTF-8                 
#>  tz       America/New_York            
#>  date     2018-08-07
#> Packages -----------------------------------------------------------------
#>  package    * version   date       source                          
#>  assertthat   0.2.0     2017-04-11 CRAN (R 3.4.0)                  
#>  backports    1.1.2     2017-12-13 CRAN (R 3.4.3)                  
#>  base       * 3.4.3     2017-12-07 local                           
#>  bindr        0.1.1     2018-03-13 cran (@0.1.1)                   
#>  bindrcpp   * 0.2.2     2018-03-29 CRAN (R 3.4.4)                  
#>  bitops       1.0-6     2013-08-17 CRAN (R 3.4.0)                  
#>  colorspace   1.3-2     2016-12-14 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      * 0.7.6     2018-06-29 CRAN (R 3.4.4)                  
#>  evaluate     0.10.1    2017-06-24 CRAN (R 3.4.1)                  
#>  ggplot2    * 3.0.0     2018-07-03 CRAN (R 3.4.4)                  
#>  glue         1.3.0     2018-07-17 cran (@1.3.0)                   
#>  graphics   * 3.4.3     2017-12-07 local                           
#>  grDevices  * 3.4.3     2017-12-07 local                           
#>  grid         3.4.3     2017-12-07 local                           
#>  gtable       0.2.0     2016-02-26 CRAN (R 3.4.0)                  
#>  htmltools    0.3.6     2017-04-28 CRAN (R 3.4.0)                  
#>  knitr        1.17      2017-08-10 CRAN (R 3.4.1)                  
#>  labeling     0.3       2014-08-23 CRAN (R 3.4.0)                  
#>  lazyeval     0.2.1     2017-10-29 CRAN (R 3.4.2)                  
#>  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                           
#>  munsell      0.5.0     2018-06-12 cran (@0.5.0)                   
#>  pillar       1.1.0     2018-01-14 cran (@1.1.0)                   
#>  pkgconfig    2.0.1     2017-03-21 CRAN (R 3.4.0)                  
#>  plyr         1.8.4     2016-06-08 CRAN (R 3.4.0)                  
#>  purrr        0.2.5     2018-05-29 CRAN (R 3.4.4)                  
#>  R6           2.2.2     2017-06-17 CRAN (R 3.4.0)                  
#>  Rcpp         0.12.18   2018-07-23 cran (@0.12.18)                 
#>  RCurl        1.95-4.10 2018-01-04 CRAN (R 3.4.3)                  
#>  reshape2     1.4.3     2017-12-11 CRAN (R 3.4.3)                  
#>  rlang        0.2.1     2018-05-30 CRAN (R 3.4.4)                  
#>  rmarkdown    1.8       2017-11-17 CRAN (R 3.4.2)                  
#>  rprojroot    1.3-2     2018-01-03 cran (@1.3-2)                   
#>  scales       1.0.0     2018-08-06 Github (hadley/scales@9b82318)  
#>  stats      * 3.4.3     2017-12-07 local                           
#>  stringi      1.2.4     2018-07-20 cran (@1.2.4)                   
#>  stringr      1.3.1     2018-05-10 CRAN (R 3.4.4)                  
#>  tibble       1.4.2     2018-01-22 cran (@1.4.2)                   
#>  tidyselect   0.2.4     2018-02-26 cran (@0.2.4)                   
#>  tools        3.4.3     2017-12-07 local                           
#>  utils      * 3.4.3     2017-12-07 local                           
#>  withr        2.1.2     2018-07-31 Github (jimhester/withr@fe56f20)
#>  XML          3.98-1.9  2017-06-19 CRAN (R 3.4.1)                  
#>  yaml         2.1.16    2017-12-12 CRAN (R 3.4.3)

[paleolimbot]

An even more minimal example. Apparently it occurs only on render...drawing and building are fine. The layer data also appears to be fine.

library(ggplot2)

df_all_vars <- expand.grid(letter = c("a", "b"), number = c(1, 2), x = 1, y = 1)
df_some_vars <- data.frame(letter = c("a", "b"), x = 2, y = 2)

p <- ggplot() +
  geom_point(aes(x, y), data = df_all_vars) +
  geom_point(aes(x, y), data = df_some_vars) +
  facet_wrap(vars(letter, number))

built <- ggplot_build(p)
drawn <- ggplot_gtable(built)
plot(drawn)
#> Error in gList(structure(list(x = structure(0.5, class = "unit", valid.unit = 0L, unit = "npc"), : only 'grobs' allowed in "gList"

# layer data appears to be fine
built$data[[2]][c("x", "y", "PANEL")]
#>   x y PANEL
#> 1 2 2     1
#> 2 2 2     3
#> 3 2 2     2
#> 4 2 2     4

^{Created on 2019-05-01 by the reprex package (v0.2.1)}

[paleolimbot]

Apparently the offending objects are objects of class gTableChild that are trying to be in a gList:

[[1]]
$wrapvp
viewport[panel-2-1.13-5-13-5]

$name
[1] "panel-2-1.13-5-13-5"

attr(,"class")
[1] "gTableChild" "list"

[[2]]
$wrapvp
viewport[panel-1-2.8-9-8-9]

$name
[1] "panel-1-2.8-9-8-9"

attr(,"class")
[1] "gTableChild" "list"

[[3]]
$wrapvp
viewport[panel-2-2.13-9-13-9]

$name
[1] "panel-2-2.13-9-13-9"

attr(,"class")
[1] "gTableChild" "list"

[paleolimbot]

The problem is in combine_vars():

library(ggplot2)
df_all_vars <- expand.grid(letter = c("a", "b"), number = c(1, 2))
df_some_vars <- data.frame(letter = c("a", "b"))

combine_vars(
  list(df_all_vars),
  env = emptyenv(),
  vars = vars(letter = letter, number = number)
)
#>   letter number
#> 1      a      1
#> 2      b      1
#> 3      a      2
#> 4      b      2

combine_vars(
  list(df_all_vars, df_some_vars),
  env = emptyenv(),
  vars = vars(letter = letter, number = number)
)
#>    letter number
#> 1       a      1
#> 2       b      1
#> 3       a      2
#> 4       b      2
#> 5       a      1
#> 6       a      1
#> 7       a      2
#> 8       a      2
#> 9       b      1
#> 10      b      1
#> 11      b      2
#> 12      b      2

^{Created on 2019-05-03 by the reprex package (v0.2.1)}

[lock]

This old issue has been automatically locked. If you believe you have found a related problem, please file a new issue (with reprex) and link to this issue. https://reprex.tidyverse.org/