如何在Rmarkdown表格的表头下方添加分隔线？

你可以通过修改row_spec()函数对表头行（第0行）的设置，直接添加底部边框来实现需求。

原代码 #

library(knitr)
library(kableExtra)

x <- cbind(c("Term", "Intercept"),
           c( "Estimate", round(2.684698447, digits = 3)), 
           c("P-value", "$< 2 \\times 10^{-16}$"),
           c("Significance", "***"))


knitr::kable(x, align="c", escape = F, caption = "Summary of the fitted linear model with miles per gallon as the response variable. Significance codes: 0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1",
      booktabs = T) %>%
  kable_styling("hover", full_width = F, font_size = 11, latex_options = "hold_position"
                )%>%
  row_spec(0, bold = T, font_size = 12) %>%
  column_spec(1, border_right = TRUE)  %>%
  row_spec(3, hline_after = TRUE)

修改后的代码 #

只需要在表头行的row_spec()中添加border_bottom = TRUE参数，就能在表头下方生成一条分隔线：

library(knitr)
library(kableExtra)

x <- cbind(c("Term", "Intercept"),
           c( "Estimate", round(2.684698447, digits = 3)), 
           c("P-value", "$< 2 \\times 10^{-16}$"),
           c("Significance", "***"))


knitr::kable(x, align="c", escape = F, caption = "Summary of the fitted linear model with miles per gallon as the response variable. Significance codes: 0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1",
      booktabs = T) %>%
  kable_styling("hover", full_width = F, font_size = 11, latex_options = "hold_position"
                )%>%
  row_spec(0, bold = T, font_size = 12, border_bottom = TRUE) %>% # 添加表头底部边框
  column_spec(1, border_right = TRUE)  %>%
  row_spec(3, hline_after = TRUE)

补充说明 #

如果你想要适配booktabs风格的细线，可以改用hline_after = TRUE参数替代border_bottom = TRUE，生成的线条会符合booktabs的排版规范：

row_spec(0, bold = T, font_size = 12, hline_after = TRUE)

内容的提问来源于stack exchange，提问作者Abbas