R Under development (unstable) (2021-10-13 r81047) -- "Unsuffered Consequences"
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> library(grid)
> 
> ## Set up
> grid.newpage()
> pushViewport(viewport(name="a.vp"))
> grid.rect(name="a.grob")
> 
> ## Default finds only grobs (no vpPath)
> result <- grid.grep("a", grep=TRUE, global=TRUE)
> result
[[1]]
a.grob 

> attr(result[[1]], "vpPath")
[1] ""
> 
> ## 'viewports = TRUE' (and 'vpPath = TRUE')
> ## finds grobs and viewports (AND vpPath on grobs)
> result <- grid.grep("a", grep=TRUE, global=TRUE, viewports=TRUE)
> result
[[1]]
a.vp 

[[2]]
a.grob 

> attr(result[[2]], "vpPath")
[1] "a.vp"
> 
> ## 'viewports = FALSE' and 'vpPath = TRUE'
> ## finds only grobs AND vpPath on grobs
> result <- grid.grep("a", grep=TRUE, global=TRUE, vpPath=TRUE)
> result
[[1]]
a.grob 

> attr(result[[1]], "vpPath")
[1] "a.vp"
> 
> ## 'viewports = TRUE' and 'vpPath = FALSE'
> ## finds viewports and grobs (no vpPath)
> result <- grid.grep("a", grep=TRUE, global=TRUE, viewports=TRUE, vpPath=FALSE)
> result
[[1]]
a.vp 

[[2]]
a.grob 

> attr(result[[2]], "vpPath")
[1] ""
> 
> ###########################
> ## global=FALSE versions
> 
> ## grob (no vpPath)
> result <- grid.grep("a", grep=TRUE)
> result
a.grob 
> attr(result, "vpPath")
[1] ""
> ## viewport (NULL vpPath)
> result <- grid.grep("a", grep=TRUE, viewports=TRUE)
> result
a.vp 
> attr(result, "vpPath")
NULL
> ## grob with vpPath
> result <- grid.grep("a", grep=TRUE, vpPath=TRUE)
> result
a.grob 
> attr(result, "vpPath")
[1] "a.vp"
> ## viewport (NULL vpPath)
> result <- grid.grep("a", grep=TRUE, viewports=TRUE, vpPath=FALSE)
> result
a.vp 
> attr(result, "vpPath")
NULL
> 
> proc.time()
   user  system elapsed 
  0.235   0.032   0.252