ggplot2 facet绘图：显示所有子图X轴及美化需求咨询

1. 让所有子图显示X轴 #

ggplot2的facet_wrap默认仅底部子图显示X轴，要让所有8个子图都显示X轴，只需在theme中强制开启X轴文本、刻度，并调整分面标题位置避免遮挡：

plotcircad <- ggplot(circad, aes(x=hourr,y=mean_d)) + 
  geom_col() +
  geom_errorbar(aes(ymax=mean_d+std_d, ymin=mean_d), size=0.25, width=0.25, 
                show.legend=FALSE, col="black") +
  xlab("Time slot") + 
  ylab("Mean (sd) distance from nest (m)") +
  facet_wrap(~ring, scales="free_y") + 
  theme_classic() + 
  theme(
    axis.line.x = element_line(colour='black', size=0.5, linetype='solid'),
    axis.line.y = element_line(colour='black', size=0.5, linetype='solid'),
    panel.background = element_blank(),
    # 强制所有子图显示X轴文本与刻度，旋转标签避免重叠
    axis.text.x = element_text(angle=45, vjust=1, hjust=1),
    axis.ticks.x = element_line(),
    # 将分面标题移到面板上方，不遮挡X轴
    strip.placement = "outside"
  )

2. 实现柱状图颜色随昼夜临近渐变 #

首先给数据集添加一个表示昼夜强度的变量（比如离正午/午夜越近，值越大），再通过颜色映射实现渐变效果：

# 新增昼夜强度变量：白天离正午越近值越大，夜晚离午夜越近值越大
circad$intensity <- ifelse(circad$hourr >=6 & circad$hourr <=18,
                           abs(circad$hourr - 12),
                           abs(circad$hourr - 0))

# 修改绘图代码，添加颜色映射
plotcircad <- ggplot(circad, aes(x=hourr,y=mean_d, fill=intensity)) + 
  geom_col() +
  geom_errorbar(aes(ymax=mean_d+std_d, ymin=mean_d), size=0.25, width=0.25, 
                show.legend=FALSE, col="black") +
  xlab("Time slot") + 
  ylab("Mean (sd) distance from nest (m)") +
  facet_wrap(~ring, scales="free_y") + 
  theme_classic() + 
  theme(
    axis.line.x = element_line(colour='black', size=0.5, linetype='solid'),
    axis.line.y = element_line(colour='black', size=0.5, linetype='solid'),
    panel.background = element_blank(),
    axis.text.x = element_text(angle=45, vjust=1, hjust=1),
    axis.ticks.x = element_line(),
    strip.placement = "outside"
  ) +
  # 设置渐变配色，可根据需求调整option参数
  scale_fill_viridis_c(option="magma", name="Proximity to\nMidday/Midnight")

3. 在黎明/黄昏柱状图顶部添加太阳/月亮图标 #

可以直接使用emoji表情快速实现，步骤如下：

# 筛选黎明（假设为6点）和黄昏（假设为18点）的数据点
dawn_dusk <- circad %>% filter(hourr %in% c(6, 18))
# 为不同时间点分配对应emoji
dawn_dusk$icon <- ifelse(dawn_dusk$hourr ==6, "☀️", "🌙")

# 在绘图代码中添加图标层
plotcircad <- ggplot(circad, aes(x=hourr,y=mean_d, fill=intensity)) + 
  geom_col() +
  geom_errorbar(aes(ymax=mean_d+std_d, ymin=mean_d), size=0.25, width=0.25, 
                show.legend=FALSE, col="black") +
  # 添加太阳/月亮图标，vjust控制图标与柱子顶部的距离
  geom_text(data=dawn_dusk, aes(label=icon), vjust=-0.5, size=6) +
  xlab("Time slot") + 
  ylab("Mean (sd) distance from nest (m)") +
  facet_wrap(~ring, scales="free_y") + 
  theme_classic() + 
  theme(
    axis.line.x = element_line(colour='black', size=0.5, linetype='solid'),
    axis.line.y = element_line(colour='black', size=0.5, linetype='solid'),
    panel.background = element_blank(),
    axis.text.x = element_text(angle=45, vjust=1, hjust=1),
    axis.ticks.x = element_line(),
    strip.placement = "outside"
  ) +
  scale_fill_viridis_c(option="magma", name="Proximity to\nMidday/Midnight")

如果需要更精细的自定义图标，可使用ggimage包加载本地图标文件，示例：

library(ggimage)
# 假设本地有sun.png和moon.png图标文件
dawn_dusk$icon_path <- ifelse(dawn_dusk$hourr ==6, "sun.png", "moon.png")
geom_image(data=dawn_dusk, aes(image=icon_path), vjust=-0.5, size=0.06)

内容的提问来源于stack exchange，提问作者Devon