Log10 Y 轴从 0 开始

Question

我创建了一个条形图来显示不同地点和层的积水差异。因为一个值远高于其他值，所以我想将 y 轴设置为 log10 刻度。这一切都有效，但结果看起来相当不直观。是否可以将 y 轴的限制设置为 0，以使值为 0.2 的条不向下？

这是我使用的代码：

p2 <- ggplot(data_summary2, aes(x= Site, y= small_mean, fill= Depth, Color= Depth))+
  geom_bar(stat = "identity", position = "dodge", alpha=1)+
  geom_errorbar(aes(ymin= small_mean - sd, ymax= small_mean + sd),
                position = position_dodge(0.9),width=0.25,   alpha= 0.6)+
  scale_fill_brewer(palette = "Greens")+
  geom_text(aes(label=small_mean),position=position_dodge(width=0.9), vjust=-0.25, hjust= -0.1, size= 3)+
  #geom_text(aes(label= Tukey), position= position_dodge(0.9), size=3, vjust=-0.8, hjust= -0.5, color= "gray25")+
  theme_bw()+
  theme(legend.position = c(0.2, 0.9),legend.direction = "horizontal")+
  theme(panel.grid.major = element_blank(), panel.grid.minor = element_blank())+
  labs(fill="Depth [cm]")+
  theme(axis.text.x = element_text(angle = 25, size =9, vjust = 1, hjust=1))+
  scale_x_discrete(labels= c( "Site 1\n(Hibiscus tillaceus)","Site 2 \n(Ceiba pentandra)","Site 3 \n(Clitoria fairchildiana)","Site 4 \n(Pachira aquatica)"))+
  #theme(legend.position = c(0.85, 0.7))+
  labs(x= "Sites\n(Type of Tree)", y= "µg Deep-Water/ g rhizosphere soil", title = "Average microbial Deep-water incorporation per Site", subtitle = "Changes over Time and Depth")+
  facet_grid(.~Time, scale = "free")
p2 + scale_y_continuous(trans = "log10")

剧情是这样的：

Answer 1

在对数刻度上没有0，因此条形图的唯一合理起点是y = 10^0 或1。

但是，您可以使用 scales::pseudo_log_trans 创建一个伪对数刻度，以将 0 包含在轴上，以便所有条形图都具有相同的方向。我借用this 的答案。 注意将0 添加到breaks 以明确这是一个伪对数刻度很重要。比较下面的两个图：

library(tidyverse)
library(scales)

# make up data with distribution positive values above and below 1
d <- tibble(grp = LETTERS[1:5],
            val = 10^(-2:2))

# normal plot with true log scale doesn't contain 0
d %>%
  ggplot(aes(x = grp, y = val, fill = grp)) +
  geom_col() +
  ggtitle("On True Log Scale Bars Start at y = 1") +
  scale_y_log10() # or if you prefer: scale_y_continuous(trans = "log10")

# set range of 'linear' portion of pseudolog scale
sigma <- min(d$val)
  
# plot on pseudolog to get all bars to extend to 0
d %>%
  ggplot(aes(x = grp, y = val, fill = grp)) +
  geom_col() +
  ggtitle("On Pseudolog Scale Bars Start at y = 0") +
  scale_y_continuous(
    trans = pseudo_log_trans(base = 10, sigma = sigma),
    breaks = c(0, 10^(-2:2)),
    labels = label_number(accuracy = 0.01)
  )

^{由reprex package (v2.0.1) 于 2021 年 12 月 30 日创建}