如何在R Markdown中使用kbl减少表格列间距

我用R Markdown结合kableExtra包创建了如下表格，但生成的表格列间距过大。已经通过column_spec设置了列宽，希望在不改动列宽的前提下缩小列之间的间距，请问该如何实现？

```{r table_r_3, message=FALSE, warning=FALSE, echo=FALSE}
library(kableExtra)

tab <- matrix(c("Description that takes 43 characters +123","2.89*** (1.12-3.90)","2.89*** (1.12-3.90)","2.89*** (1.12-3.90)","2.89 (1.12-3.90)","2.89*** (1.12-3.90)","2.89*** (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)",
                "Description that takes 43 characters +123","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)",
                "Description that takes 43 characters +123","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)",
                "Description that takes 43 characters +123","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)",
                "Description that takes 43 characters +123","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)",
                "Description that takes 43 characters +123","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)",
                "Description that takes 43 characters +123","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)",
                "Description that takes 43 characters +123","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)",
                "Description that takes 43 characters +123","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)",
                "Description that takes 43 characters +123","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)",
                "Description that takes 43 characters +123","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)",
              "Description that takes 43 characters +123","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)",
              "Description that takes 43 characters +123","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)","2.89 (1.12-3.90)"
              ), ncol=13, byrow=TRUE)
colnames(tab) <- c(' ','A1','A2','A1','A2','A1','A2','A1','A2','A1','A2','A1','A2')
rownames(tab) <- NULL
tab <- as.table(tab)

table_r_3_output <- kbl(tab, booktabs = T, linesep = "", row.names = 0, caption = "Results.") %>%
  kable_styling(font_size = 5, latex_options = "hold_position") %>%
add_header_above(c(" " = 1, "Grp1 & Grp2" = 2, "Grp1" = 2, "Grp1 & Grp2" = 2, "Grp1" = 2, "Grp1 & Grp2" = 2, "Grp1" = 2)) %>%
add_header_above(c(" " = 1, "Jan 2015 - Dec 2017" = 4, "Jan 2016 - Dec 2016" = 4, "Jan 2017 - Dec 2017" = 4),
                 escape = FALSE) %>%
  column_spec(1, width = "19em") %>%
  column_spec(c(2:13), width = "5em")

table_r_3_output

---

# 解决方案
要在保留现有列宽的前提下缩小列间距，核心是调整LaTeX表格的`\tabcolsep`参数（该参数控制列与列之间的空白宽度，默认值通常为6pt），以下两种方法均可实现：

## 方法1：在`kbl()`中直接添加LaTeX命令
在`kbl()`函数的`extra`参数中插入`\setlength{\tabcolsep}{<数值>pt}`，自定义列间距大小（示例设为2pt，可根据可读性调整）：
```r
table_r_3_output <- kbl(tab, booktabs = T, linesep = "", row.names = 0, caption = "Results.",
                       # 新增这一行，调整列间距
                       extra = "\\setlength{\\tabcolsep}{2pt}") %>%
  kable_styling(font_size = 5, latex_options = "hold_position") %>%
  add_header_above(c(" " = 1, "Grp1 & Grp2" = 2, "Grp1" = 2, "Grp1 & Grp2" = 2, "Grp1" = 2, "Grp1 & Grp2" = 2, "Grp1" = 2)) %>%
  add_header_above(c(" " = 1, "Jan 2015 - Dec 2017" = 4, "Jan 2016 - Dec 2016" = 4, "Jan 2017 - Dec 2017" = 4),
                   escape = FALSE) %>%
  column_spec(1, width = "19em") %>%
  column_spec(c(2:13), width = "5em")

方法2：通过add_footnote()实现局部生效 #

如果不想影响文档中的其他表格，可利用LaTeX分组机制，通过add_footnote()将列间距设置限定在当前表格范围内：

table_r_3_output <- kbl(tab, booktabs = T, linesep = "", row.names = 0, caption = "Results.") %>%
  kable_styling(font_size = 5, latex_options = "hold_position") %>%
  add_header_above(c(" " = 1, "Grp1 & Grp2" = 2, "Grp1" = 2, "Grp1 & Grp2" = 2, "Grp1" = 2, "Grp1 & Grp2" = 2, "Grp1" = 2)) %>%
  add_header_above(c(" " = 1, "Jan 2015 - Dec 2017" = 4, "Jan 2016 - Dec 2016" = 4, "Jan 2017 - Dec 2017" = 4),
                   escape = FALSE) %>%
  column_spec(1, width = "19em") %>%
  column_spec(c(2:13), width = "5em") %>%
  # 新增这一行，局部调整列间距
  add_footnote("\\setlength{\\tabcolsep}{2pt}", escape = FALSE, footnote_as_chunk = TRUE)

原理说明 #

\tabcolsep是LaTeX表格的核心参数，控制列边缘之间的水平空白距离。调整该参数的数值时，column_spec设置的列宽不会受到影响，只会改变列与列之间的空隙大小。建议在1pt-4pt之间测试，找到兼顾紧凑性和可读性的数值。

内容的提问来源于stack exchange，提问作者Dan