用网格和gtable拆除ggplot [英] dismantling a ggplot with grid and gtable

问题描述

我正努力根据 ggplot 对象构建双轴图。根据baptiste的建议，我已将问题分解成更小的部分。现在的问题是：如何从 grobs 中删除​​所有数据。 $ c>，同时保留坐标轴，轴标签，坐标轴标记和网格线？'data'是指与 geom_line（）和 geom_points（）。


想要这样做的原因在构建双轴图的过程中，我遇到了以下问题：来自一个grob的网格线会覆盖另一个grob的数据。

让我明确一点：我的解决方法是将线型添加到aes（）和设置scale_linetype_manual（values = c（solid，blank）或者将数据从网格中发送出去，但是我想后处理一个没有被修饰太多

以下是一些代码和数字。

 ＃数据
 df < - 结构（列表（年份= c（1950,2013,1950,2013），国家=结构（c（1L，
 1L，2L，2L），。标签= c 小时最低工资，小时最低工资，
小时最低工资，小时最低工资，小时最低工资 （2013年欧元），美国（2013年），b美元（2013美元）
），单位= c（2013年欧元，2013年欧元，2013美元， 2013美元
）），.Names = c（Year，Country，Category，value，variable，
Unit），row.names = c （数据框架）（b）数据框架（b）数据框架（ggplot2）
p < -  ggplot（data = df，aes（NA，4L），class =data.frame）
 
＃ x = Year，y = value，group = variable，color = variable，shape = variable））+ 
 geom_line（size = 2）+ 
 geom_point（size = 4）+ 
 theme panel.grid.major = element_line（size = 1，color =darkgreen），
 panel.grid.minor = element_line（size = 1，color =darkgreen，linetype =dotted））
 
＃使用gtable操作grobs 
 library（gtable）
g<  -  ggplot_gtable（ggplot_build（p））
 ##这里删除geom_line（）和geom_point（）
 ## g < -  stripdata（g）＃伪代码！ 
 grid.newpage（）
 grid.draw（g）
  

在下面的阴谋，我想线去！

编辑：按照baptiste的建议，我尝试删除数据图层。但是，BondedDust在注释部分指出，这会打破ggplot对象：

 ＃删除两层数据
p $ layers [[1]]<  -  NULL 
p $ layers [[1]]<  -  NULL 
g<  -  ggplot_gtable（ggplot_build（p））
 ##错误：图中没有图层
  

从ggplot对象中删除数据会破坏它。我在应用程序中使用的一种解决方法是将数据从网格发送，例如将每个单元乘以-999999并用 + scale_y_continuous（limits = c（1，10））切断显示，但是我想避免这种丑陋的黑客行为，如果可行。我希望如果我用NA或NULL替换每个数据点，关联的gtable不会被销毁，所以我正在寻找一种从g对象内部而不是p对象中删除数据的方法。

在操作grobs（而不是直接对ggplot对象进行攻击）之后， grid.draw（g）的结果会be：

仅供参考，第二个图是通过以下解决方法获得的。

  p < ;  -  ggplot（data = within（df，value <-999999），aes（x = Year，y = value，group = variable，color = variable，shape = variable））+ 
 geom_line（）+ 
 geom_point（）+ 
主题（panel.grid.major = element_line（size = 1，color =darkgreen），
 panel.grid.minor = element_line（size = 1，color =darkgreen，linetype =dotted））+ 
 scale_y_continuous（limits = c（1，10））
  

解决方案

更自然的策略是使用隐藏的 geom_blank 图层，以便ggplot2仍然训练刻度等来建立情节，但没有显示数据。但是，由于您要处理已格式化的图块，因此可能必须手动从图形gTree中删除这些图块。这是一个尝试，

  library（gtable）
g < -  ggplotGrob（p）
 
 stripdata<  -  function（g）{
 keep<  -  grepl（border | grill，
 names（g [[grobs]] [[4]] [[ ]]））
g [[grobs]] [[4]] [[children]] [！keep]<  -  NULL 
g 
} 
 
 grid.newpage（）
 grid.draw（stripdata（g））
  

I'm struggling to build a dual-axis plot based on ggplot objects. At baptiste's suggestion, I have broken down the problem into smaller parts. The present issue is:

1. how to remove all of the data from the grobs, while keeping the axis, the axis labels, the axis tickmarks, and the grid lines? By 'data' I mean the data associated with geom_line() and geom_points().

The reason for wanting to do this is that in the process of building a dual-axis plot, I ran into the following problem: the grid lines from one grob would overwrite the data from the other grob. By removing the data lines and points, there would be no overwriting.

Let me be clear: I do have workarounds that consist in adding a linetype to the aes() and setting scale_linetype_manual(values = c("solid", "blank") or, alternatively, sending the data 'off the grid', but I would like to post-process a plot object that has not been 'groomed' too much for the purpose at hand.

Below some code and figures.

# Data
df <- structure(list(Year = c(1950, 2013, 1950, 2013), Country = structure(c(1L, 
1L, 2L, 2L), .Label = c("France", "United States"), class = "factor"), 
Category = c("Hourly minimum wage", "Hourly minimum wage", 
"Hourly minimum wage", "Hourly minimum wage"), value = c(2.14, 
9.43, 3.84, 7.25), variable = c("France (2013 euros)", 
"France (2013 euros)", "United States (2013 dollars)", "United States (2013 dollars)"
), Unit = c("2013 euros", "2013 euros", "2013 dollars", "2013 dollars"
)), .Names = c("Year", "Country", "Category", "value", "variable", 
"Unit"), row.names = c(NA, 4L), class = "data.frame")

# Plot data with ggplot
library(ggplot2)
p <- ggplot(data = df, aes(x = Year, y = value, group = variable, colour = variable, shape = variable)) + 
geom_line(size = 2) + 
geom_point(size = 4) +
theme(panel.grid.major = element_line(size = 1, colour = "darkgreen"), 
      panel.grid.minor = element_line(size = 1, colour = "darkgreen", linetype = "dotted"))

# Manipulate grobs with gtable
library(gtable)
g <- ggplot_gtable(ggplot_build(p))
## Here remove the geom_line() and geom_point()
## g <- stripdata(g)  # pseudo-code!
grid.newpage()
grid.draw(g)

In the plot below, I would like the lines gone!

Edit: Following baptiste's suggestion, I attempt to remove the data layers. However, as BondedDust points out in the comments section, this breaks the ggplot object:

# Remove the two layers of data
p$layers[[1]] <- NULL
p$layers[[1]] <- NULL
g <- ggplot_gtable(ggplot_build(p))
## Error: No layers in plot

Removing the data from the ggplot object destroys it. One workaround I have used in applications is to 'send the data off the grid', e.g. multiplying each cell by -999999 and cuting off the display with + scale_y_continuous(limits = c(1, 10)), but I'd like to avoid this ugly hack, if feasible. I was hoping that the associated gtable would not be destroyed if I replaced every data point with NA or NULL, so that's why I was looking for a way to remove the data from inside the g object, rather than the p object.

After manipulation of the grobs (rather than hacking directly the ggplot object), the result of grid.draw(g) would be:

FYI, the second plot was obtained with the following workaround.

p <- ggplot(data = within(df, value <- -999999), aes(x = Year, y = value, group = variable, colour = variable, shape = variable)) + 
geom_line() + 
geom_point() +
theme(panel.grid.major = element_line(size = 1, colour = "darkgreen"), 
      panel.grid.minor = element_line(size = 1, colour = "darkgreen", linetype = "dotted")) +
scale_y_continuous(limits = c(1, 10))

解决方案

A more natural strategy would be to use invisible geom_blank layers, so that ggplot2 still trains the scales etc to build the plot but shows no data. Since you want to process already-formatted plots, however, you probably have to remove manually those grobs from the plot gTree. Here's an attempt,

library(gtable)
g <- ggplotGrob(p)

stripdata <- function(g){
  keep <- grepl("border|grill", 
                names(g[["grobs"]][[4]][["children"]]))
  g[["grobs"]][[4]][["children"]][!keep] <- NULL
  g
}

grid.newpage()
grid.draw(stripdata(g))

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