R语言ggplot2：geom_rect中换行文本的对齐与居中问题

数据准备代码 #

Channel <- c("Episode", "Episode", "Episode", "Episode", "Episode", "Episode", "Episode", "Episode")
start.time <- c(0.000, 25.458, 48.712, 152.419, 179.055, 196.274, 212.693, 232.861)
stop.time <- c(25.458, 48.712, 152.419, 179.055, 196.274, 212.693, 232.861, 266.370)
Episode <- c("Prologue", "An episode title", "A longer episode title", "An really, incredibly long episode title", "I wish I knew how to make hjust work with wrapped text", "A sample title", "No one likes making reproducible examples", "Epilogue")

ep_df <- data.frame(Channel, start.time, stop.time, Episode)
#wrap text for episode titles
ep_df$Episode <- stringr::str_wrap(ep_df$Episode, 15)

绘图代码 #

library(ggplot2)
ggplot(ep_df, aes(fill = Episode, color = Episode)) + 
  geom_rect(color = "black", aes(xmin = start.time, xmax = stop.time, ymin = -0.5, ymax = 0.5), show.legend = FALSE) +
  scale_x_continuous(breaks = scales::pretty_breaks(n = 15)) +
  facet_grid(Channel ~ .) +
  theme(axis.text.y=element_blank(), 
        axis.ticks.y=element_blank()) + 
  coord_fixed(40)+ scale_fill_manual(values=c("#F8F8F8", "#F5F5F5", "#F0F0F0", "#E8E8E8", "#E0E0E0", "#DCDCDC", "#D8D8D8", "#D3D3D3", "#D0D0D0", "#C8C8C8")) +
  theme(legend.position="bottom") + 
  geom_text(hjust = -0.5, vjust = 0.5, size = 2, aes(x = pmin(start.time, (start.time+stop.time)/2), y = 0, label = Episode), inherit.aes = FALSE) + 
  theme(plot.margin = margin(t = 0)) +
  labs(x = "Time (sec)") +
  ylab(NULL)

遇到的问题 #

• 使用hjust对齐矩形内的文本时，仅第一行生效，后续行错位，希望换行文本的每行都能对齐同一左边缘（不紧贴矩形左边界）；
• 无法实现文本在矩形块内居中，hjust似乎不起作用，能否实现文本随矩形大小自动居中？（第二个问题无法解决也可接受）

解决换行文本左对齐问题 #

要让换行后的每行文本保持同一左边缘对齐，只需调整geom_text的对齐参数与锚点位置：

• 将hjust设为0（左对齐模式），所有换行行都会以指定的x坐标为左基准对齐；
• 把x坐标设为start.time + 1（1为偏移量，可根据需求调整），避免文本紧贴矩形左边界；
• 保持vjust=0.5确保文本在垂直方向居中，添加lineheight参数优化行间距。

修改后的完整绘图代码：

library(ggplot2)
library(stringr)

ggplot(ep_df, aes(fill = Episode, color = Episode)) + 
  geom_rect(color = "black", aes(xmin = start.time, xmax = stop.time, ymin = -0.5, ymax = 0.5), show.legend = FALSE) +
  scale_x_continuous(breaks = scales::pretty_breaks(n = 15)) +
  facet_grid(Channel ~ .) +
  theme(axis.text.y=element_blank(), 
        axis.ticks.y=element_blank()) + 
  coord_fixed(40)+ 
  scale_fill_manual(values=c("#F8F8F8", "#F5F5F5", "#F0F0F0", "#E8E8E8", "#E0E0E0", "#DCDCDC", "#D8D8D8", "#D3D3D3", "#D0D0D0", "#C8C8C8")) +
  theme(legend.position="bottom") + 
  geom_text(hjust = 0, vjust = 0.5, size = 2, lineheight = 0.8,
            aes(x = start.time + 1, y = 0, label = Episode), inherit.aes = FALSE) + 
  theme(plot.margin = margin(t = 0)) +
  labs(x = "Time (sec)") +
  ylab(NULL)

可选：实现文本在矩形内自动居中 #

如果需要让文本随矩形大小自动居中，需要结合矩形宽度动态调整文本换行宽度，并设置居中对齐：

1. 根据每个矩形的宽度（stop.time - start.time）估算合适的换行宽度，让文本适配矩形空间；
2. 将geom_text的hjust设为0.5，x坐标设为矩形中点(start.time + stop.time)/2。

示例代码：

library(ggplot2)
library(stringr)

# 按矩形宽度动态调整换行宽度（比例可按需微调）
ep_df$Episode <- mapply(function(txt, width) {
  str_wrap(txt, width = round(width / 1.5))
}, ep_df$Episode, ep_df$stop.time - ep_df$start.time)

ggplot(ep_df, aes(fill = Episode, color = Episode)) + 
  geom_rect(color = "black", aes(xmin = start.time, xmax = stop.time, ymin = -0.5, ymax = 0.5), show.legend = FALSE) +
  scale_x_continuous(breaks = scales::pretty_breaks(n = 15)) +
  facet_grid(Channel ~ .) +
  theme(axis.text.y=element_blank(), 
        axis.ticks.y=element_blank()) + 
  coord_fixed(40)+ 
  scale_fill_manual(values=c("#F8F8F8", "#F5F5F5", "#F0F0F0", "#E8E8E8", "#E0E0E0", "#DCDCDC", "#D8D8D8", "#D3D3D3", "#D0D0D0", "#C8C8C8")) +
  theme(legend.position="bottom") + 
  geom_text(hjust = 0.5, vjust = 0.5, size = 2, lineheight = 0.8,
            aes(x = (start.time + stop.time)/2, y = 0, label = Episode), inherit.aes = FALSE) + 
  theme(plot.margin = margin(t = 0)) +
  labs(x = "Time (sec)") +
  ylab(NULL)

内容的提问来源于stack exchange，提问作者Wangana