ggplot-将刻度线与轴对齐

Question

我在这里使用@ jan-glx解释的ndodge函数； https://stackoverflow.com/a/60650595/13399047

但是，例如，我无法弄清楚如何对齐轴刻度线。

我可能应该使用theme（axis.ticks.length =），但是我不确定如何以偶数/奇数方式进行操作。

请帮助！

Answer 1

据我所知，在ggplot中没有构建此操作的方法，尽管在他们重写指南系统时可能会改变。

这既不漂亮也不容易，但这是一个示例，您可以通过在gtable /网格中弄乱来做到这一点。

library(ggplot2)
library(grid)
data(diamonds)
diamonds$cut <- paste("Super Dee-Duper",as.character(diamonds$cut))

g <- ggplot(diamonds, aes(cut, carat)) + 
  geom_boxplot() +
  scale_x_discrete(guide = guide_axis(n.dodge = 2))

# Convert to gtable
gt <- ggplotGrob(g)

# Grab bottom axis
is_axis <- grep("axis-b", gt$layout$name)
axisgrob <- gt$grobs[is_axis][[1]]
axis <- axisgrob$children$axis

# Grab tickmarks
is_ticks <- which(vapply(axis$grobs, inherits, logical(1), "polyline"))
ticks <- axis$grobs[[is_ticks]]

# Modify tickmarks
labelheight <- axis$heights[[2]] # First row of labels
modify <- which(seq_along(ticks$y) %% 4 == 0) - 1 # Change every the 3rd item in every quadruplet
ticks$y[modify] <- ticks$y[modify] - labelheight

# Insert ticks back into axis back into table
axis$grobs[[is_ticks]] <- ticks
axisgrob$children$axis <- axis
gt$grobs[[is_axis]] <- axisgrob

# Plot
grid.newpage()
grid.draw(gt)

^{由reprex package（v0.3.0）于2020-05-18创建}

Answer 2

这是一个仅使用 ggplot2 内容而不修改任何 grobs 的解决方案。它需要 ggplot2 3.0.0 并且基于 https://stackoverflow.com/a/51312611/6615512

library(ggplot2)
data(diamonds)
diamonds$cut <- paste("Super Dee-Duper",as.character(diamonds$cut))


tick_min_pos_odd = -0.6
tick_min_pos_even = -0.4
custom_ticks = data.frame(cut = sort(unique(diamonds$cut)))
n_discrete_x_values = nrow(custom_ticks)

# Alternate tick lengths
custom_ticks$tick_min_pos = ifelse(1:n_discrete_x_values %% 2 == 0, tick_min_pos_odd, tick_min_pos_even)

ggplot(diamonds, aes(cut, carat)) + 
  geom_boxplot() +
  scale_x_discrete(guide = guide_axis(n.dodge = 2)) +  
  geom_linerange(data = custom_ticks,                        # The custom tickmarks
                 aes(x=cut, ymax=-0.25, ymin=tick_min_pos), 
                 size=0.5, color='black',
                 inherit.aes = F) +
  coord_cartesian(clip='off', ylim=c(0,NA)) +        # Clip off makes it so the geoms can be drawn outside the plot
                                                     # ylim sets the y-axis from 0 to the max.
  theme(plot.margin = margin(0,0,20,0),              # Add some whitespace to the bottom of the plot
        axis.title.x = element_text(vjust=-1.5),     # nudge the x-axis title and text down a tad
        axis.text.x = element_text(vjust=-1.5))