multiline table header using knitr and latex

Question

I ended up using tables package with knitr, but I can not figure out how to get a multiline header. Here is the code:

<<test_table, results='asis', echo=FALSE>>=
matrix <- matrix(1:9, nrow = 3)
colnames(matrix) <- c("first column", "seconf column which I want to have 2     lines because of its very long header title", "third column")
library(tables)
table <- as.tabular(matrix)
latex(table)
@

Can you simply add \n, as in "seconf column which I want to have 2\nlines...? — lawyeR, Aug 13 '15 at 22:01
@dariaa, you are right. Doesn't seem to work (I also tried a simple carriage return and tried the setNames() function. I'm no Latex guru but have you looked at http://tex.stackexchange.com/questions/39253/multiline-table-header — lawyeR, Aug 14 '15 at 10:31
See also [grouped headers](https://cran.r-project.org/web/packages/kableExtra/vignettes/awesome_table_in_html.html#Grouped_Columns__Rows) i.e. "tables with multi-row headers" in the kable extra package, in case that is what you are looking for. — Paul Rougieux, Mar 17 '21 at 14:37

score 1 · Answer 1 · answered Aug 14 '15 at 10:54

It's probably possible to do this with the tables package, but xtable provides a very easy solution. The following minimal example shows two different approaches:

\documentclass{article}
\begin{document}

<<setup, echo = FALSE>>=
library(xtable)
library(knitr)
opts_chunk$set(echo = FALSE, results = "asis")

matrix <- matrix(1:9, nrow = 3)
  colnames(matrix) <- c(
    "first column",
    "second column which I want to have 2 lines because of its very long header title",
    "third column")
@

<<ChangeColumnType>>=
  print(xtable(matrix, align = c("r", "r", "p{4cm}", "r")), include.rownames = FALSE)
@

<<ChangeOnlyCell>>=
  colnames(matrix)[2] <- "\\multicolumn{1}{p{4cm}}{second column which I want to have 2 lines because of its very long header title}"
  print(xtable(matrix), include.rownames = FALSE, sanitize.colnames.function = identity)
@
\end{document}

The first approach (chunk ChangeColumnType) is very simple: It sets the column type of column 2 to p{4cm}. That gives a column that is 4cm wide with automatic text wrapping (see wikibooks.org for more details). The drawback is, that this affects the whole column, not only the cell in the first row.

The second approach (chunk ChangeOnlyCell) uses default alignment (or whatever you want to specify via align) and changes only the column type of the problematic cell using \multcolumn. By default, xtable "sanitizes" your table, meaning that all special latex characters will be escaped. This is handy because you cannot (easily) break your TEX code, but here we manually want to inject LaTeX code, so we have to turn this off. Therefore, set sanitize.colnames.function = identiy. All column names will be used as you specify them – so be careful when using characters with a special meaning in LaTeX.

The example from above delivers the following tables:

multiline table header using knitr and latex

1 Answers1