ggplot标签新行开头存在多余空格，如何实现左对齐？

使用ggplot绘制图表并添加多行标签时，部分新行开头出现多余空格，导致标签无法左对齐，需要优化实现所有标签左对齐。

原代码如下：

library(tidyverse)
library(metrica)

df = data.frame(x = 1:100 * rnorm(100,50,7),
           y = c(1:100))

label <- df %>%
  summarise(R2 = metrica::R2(obs = y, pred = x)$R2,
            RMSE = metrica::RMSE(obs = y, pred = x)$RMSE,
            rRMSE = metrica::RRMSE(obs = y, pred = x)$RRMSE,
            n = n()) %>%
  mutate(label = paste("R² = ", round(R2, 2), 
                       "\nRMSE = ", round(RMSE, 2), 
                       "\nrRMSE = ", round(rRMSE, 2),
                       '\nn = ',n, sep=''))

plt <- 
  ggplot(df,aes(x=x,y=y)) +
  geom_point() +
  geom_text(data = label, aes(x = -Inf, y = Inf, label = label), hjust = -0.1, vjust = 1.1,size=4); plt

问题图示：

方法1：使用glue构建标签（推荐） #

glue能直观拼接字符串，避免手动加空格出错，代码更易读：

label <- df %>%
  summarise(R2 = metrica::R2(obs = y, pred = x)$R2,
            RMSE = metrica::RMSE(obs = y, pred = x)$RMSE,
            rRMSE = metrica::RRMSE(obs = y, pred = x)$RRMSE,
            n = n()) %>%
  mutate(label = glue::glue("R² = {round(R2, 2)}
RMSE = {round(RMSE, 2)}
rRMSE = {round(rRMSE, 2)}
n = {n}"))

方法2：修正paste写法 #

如果坚持用paste，改用paste0（默认sep=''），同时确保换行后无多余空格：

mutate(label = paste0("R² = ", round(R2, 2), 
                     "\nRMSE = ", round(RMSE, 2), 
                     "\nrRMSE = ", round(rRMSE, 2),
                     "\nn = ", n))

优化对齐效果 #

调整geom_text的hjust参数为0，确保标签完全左对齐：

geom_text(data = label, aes(x = -Inf, y = Inf, label = label), hjust = 0, vjust = 1.1, size=4)

以上修改后，所有标签行将实现左对齐，不会出现多余空格。

内容的提问来源于stack exchange，提问作者Squan Schmaan