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Problem description

I have created an gtable (also gTree grob gDesc) object myobj via myobj <- gridExtra::grid.arrange(g1,g2) from two ggplot objects g1,g2 some time ago and now I have to restore the data that I have used to create both ggplots. Is there a way to do this properly?

What I've tried so far

I have already tried to convert myobj using various functions, e.g., ggpubr::as_ggplot, resulting in an object with a waiver() as $data entry - so no success there - and I have also swept all the grobs entries in myobj where I in fact found the data points in the plot (looking like this

grobs.grobs.children.geom_point.points.5415.x1 
                                    0.04545455

), which are, however, only the position coordinates $\in (0,1)$ w.r.t. the corresponding axis. Then I probably can get the axis + the axis range and then extrapolate the original data points. But that seems excessively laborious. Is there a more simple solution to this?

Reprex (sort of)

Not sure if this actually results in the same object as I have (because mine is almost 2y old), but for a start:

library(ggplot)

# plot 1
g1 <- ggplot(mpg, aes(displ, cty)) + geom_point() + facet_grid(cols = vars(cyl))

# plot 2
g2 <- ggplot(mtcars, aes(mpg, wt, colour = factor(cyl))) + geom_point() + facet_grid(vars(cyl))

# create object
myobj <- gridExtra::grid.arrange(g1, g2, ncol=1)

# Now I would need some extract_data function to retrieve mpg and mtcars:
list_with_mpg_and_mtcars <- extract_data(myobj)
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1 回答 1

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你不能；在这个阶段（即之后ggplotGrob），数据已被处理为图形对象，并且映射通常不可逆，就像煎蛋一样。

如果您迫切希望获得一些值，您可以检查与绘制点相对应的单个 grobs，例如

myobj$grobs[[2]]$grobs[[2]]$children[[3]][c('x','y')]

$x
 [1] 0.525145067698259native 0.587040618955513native
 [3] 0.525145067698259native 0.89651837524178native 
 [5] 0.819148936170213native 0.954545454545455native
 [7] 0.474854932301741native 0.699226305609285native
 [9] 0.648936170212766native 0.819148936170213native
[11] 0.470986460348163native

$y
 [1] 0.233037353850445native  0.435264173310709native 
 [3] 0.425966388507938native  0.205143999442133native 
 [5] 0.0691638967016109native 0.12030171311685native  
 [7] 0.266741823760489native  0.143546175123777native 
 [9] 0.191197322237977native  0.0454545454545455native
[11] 0.339961879082309native
于 2020-04-20T00:22:50.633 回答