ggplot2：从绘图中删除未使用的因子级别组合的方面（facet_grid）

Question

我想从facetted ggplot2数据中选择性地删除不必要的方面。我看了一下这个问题，但无法弄清楚如何做到这一点（也许是提醒现在有过时）：

adding empty graphs to facet_wrap in ggplot2

这里是一个小例子。我想删除右下方的空面（b，2）。

library('ggplot2') 
d <- data.frame('factor_1' = factor(c('a', 'a', 'b')), 
       'factor_2' = factor(c('1', '2', '1')), 
       x = 1:3, y = 1:3) 

ggplot(data = d, mapping = aes(x = x, y = y)) + 
    geom_point() + 
    facet_grid(facets = factor_1 ~ factor_2, drop = TRUE) 

显然drop = TRUE这里没有任何影响，因为没有未使用的因子的水平，但其仅使用新的组合。

Answer 1

在GGPLOT2 2.2.0中，grobs的出图中的名称有改变。

library(ggplot2) 
library(grid) 
d <- data.frame('factor_1' = factor(c('a', 'a', 'b')), 
       'factor_2' = factor(c('1', '2', '1')), 
       x = 1:3, y = 1:3) 

p = ggplot(data = d, mapping = aes(x = x, y = y)) + 
    geom_point() + 
    facet_grid(facets = factor_1 ~ factor_2, drop = TRUE) 

# Get ggplot grob 
g = ggplotGrob(p) 

# Get the layout dataframe. 
# Note the names. 
# You want to remove "panel-2-2" 
g$layout 

# gtable::gtable_show_layout(g) # Might also be useful 

# Remove the grobs 
# The grob needs to be remove, 
# and the relevant row in the layout data frame needs to be removed 
pos <- grepl(pattern = "panel-2-2", g$layout$name) 
g$grobs <- g$grobs[!pos] 
g$layout <- g$layout[!pos, ] 


# Alternatively, replace the grobs with the nullGrob 
g = ggplotGrob(p) 
pos <- grep(pattern = "panel-2-2", g$layout$name) 
g$grobs[[pos]] <- nullGrob() 

# If you want, move the axis 
# g$layout[g$layout$name == "axis-b-2", c("t", "b")] = c(8, 8) 

# Draw the plot 
grid.newpage() 
grid.draw(g) 

在您的链接的答案需要修改是这样的：

n <- 1000 
df <- data.frame(x = runif(n), y=rnorm(n), label = sample(letters[1:7], 
       size = n, replace = TRUE), stringsAsFactors=TRUE) 
df$label.new <- factor(df$label, levels=sort(c(""," ",levels(df$label)))) 


p <- ggplot(df, aes(x=x, y=y)) + geom_point() + 
     facet_wrap(~ label.new, ncol=3,drop=FALSE) 

g = ggplotGrob(p) 

g$layout # Note the names and their positions (t, b, l, r) 
# gtable::gtable_show_layout(g) # Might also be useful 

pos <- g$layout$name %in% c("panel-1-1", "panel-1-2", "strip-t-1-1", "strip-t-2-1") 
g$grobs <- g$grobs[!pos] 
g$layout <- g$layout[!pos, ] 

# Or replace the grobs with the nullGrob 
g = ggplotGrob(p) 
pos <- g$layout$name %in% c("panel-1-1", "panel-1-2", "strip-t-1-1", "strip-t-2-1") 
g$grobs[pos] <- list(nullGrob()) 

# Move the axis 
g$layout[g$layout$name == "axis-l-1-1", c("l", "r")] = c(10,10) 

grid.newpage() 
grid.draw(g) 

Answer 2

不是最好的解决办法，但它给了尚令人满意的结果：

d$fInter <- interaction(d$factor_2, d$factor_1, sep = ' V ') 

    ggplot(data = d, mapping = aes(x = x, y = y)) + 
     geom_point() + 
     facet_wrap(~ fInter, drop = TRUE, 
       ncol = nlevels(d$factor_1)) 

和情节：