如何更改 xtable markdown 中某些单元格的颜色？

我有一个名为 j 的数据框：

dput(j)

structure(list(Trans = c(89.8, 3337, NA, 97.55, NA, 3558.7, NA, 
4290.6, NA, 65.95, 94.55, 3495.9), `%CPU` = c(6.938, 79.853, 
1.875, 4.87, 1.46, 37.885, 1.63, 64.576, 1.165, 3.425, 5.67, 
33.856), `%Heap Used` = c(9.9, 76.95, 3.77, 9.8, 6.73, 59.23, 
3.94, 67.38, 3.73, 9.13, 9.57, 62.11), `Heap Usage/MB` = c(263.884, 
1942.246, 99.104, 257.717, 178.951, 1657.447, 99.933, 2137.134, 
96.687, 242.024, 256.302, 1646.117)), .Names = c("Trans", "%CPU", 
"%Heap Used", "Heap Usage/MB"), class = "data.frame", row.names = c(NA, 
-12L))

如果我想根据 r markdown 中的阈值对单元格进行颜色编码，我该怎么做？

例如，如果 %CPU>70，我需要将该单元格颜色编码为红色。

我可以像这样在 r markdown 中打印它：

print(xtable(j_cor,digits=2,row.names=FALSE,caption="JVM Usage"),caption.placement="top", tabular.environment="longtable",comment=FALSE,floating=FALSE)

但我喜欢根据阈值 r markdown 在单元格中放置颜色 有什么想法吗？

我尝试过类似的操作，但 pdf 文件中的颜色或单元格没有改变：

j[,2] = ifelse(j[,2] < 60, paste0("\\colorbox{red}{", j[,2], "}"), j[,2])


sessionInfo()

R version 3.2.4 (2016-03-10)
Platform: x86_64-w64-mingw32/x64 (64-bit)
Running under: Windows 7 x64 (build 7601) Service Pack 1

locale:
[1] LC_COLLATE=English_United States.1252  LC_CTYPE=English_United States.1252    LC_MONETARY=English_United States.1252
[4] LC_NUMERIC=C                           LC_TIME=English_United States.1252    

attached base packages:
[1] stats4    grid      stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
 [1] ggthemes_3.4.0    flexclust_1.3-4   modeltools_0.2-21 lattice_0.20-35   tidyr_0.6.1       jsonlite_1.4      Rcpp_0.12.10      lazyeval_0.2.0   
 [9] knitr_1.16        gridExtra_2.0.0   xtable_1.8-0      data.table_1.9.6  cowplot_0.6.2     reshape2_1.4.1    corrplot_0.77     scales_0.4.1     
[17] stringr_1.0.0     chron_2.3-47      ggplot2_2.2.1     dplyr_0.5.0       purrr_0.2.2       xml2_1.0.0        plyr_1.8.4        RCurl_1.95-4.7   
[25] bitops_1.0-6      XML_3.98-1.3      httr_1.0.0        rmarkdown_1.5    

loaded via a namespace (and not attached):
 [1] tools_3.2.4      digest_0.6.12    evaluate_0.10    tibble_1.3.0     gtable_0.2.0     DBI_0.6-1        parallel_3.2.4   yaml_2.1.14     
 [9] rprojroot_1.2    R6_2.2.1         magrittr_1.5     backports_1.1.0  htmltools_0.3.5  assertthat_0.2.0 colorspace_1.3-2 labeling_0.3    
[17] stringi_1.1.5    munsell_0.4.3 

我已将确切的文本复制到我的 Rstudio 并尝试运行它，但收到此错误：

"C:/Program Files/RStudio/bin/pandoc/pandoc" +RTS -K512m -RTS test_color.utf8.md --to latex --from markdown+autolink_bare_uris+ascii_identifiers+tex_math_single_backslash --output test_color.pdf --template "C:\R\win-library\3.2\rmarkdown\rmd\latex\default.tex" --highlight-style tango --latex-engine xelatex --variable graphics=yes --variable "geometry:margin=1in" 
! LaTeX Error: Missing \begin{document}.

See the LaTeX manual or LaTeX Companion for explanation.
Type  H <return>  for immediate help.
 ...                                              

l.1 <

pandoc.exe: Error producing PDF from TeX source
Error: pandoc document conversion failed with error 43
In addition: Warning message:
running command '"C:/Program Files/RStudio/bin/pandoc/pandoc" +RTS -K512m -RTS test_color.utf8.md --to latex --from markdown+autolink_bare_uris+ascii_identifiers+tex_math_single_backslash --output test_color.pdf --template "C:\Documents\R\win-library\3.2\rmarkdown\rmd\latex\default.tex" --highlight-style tango --latex-engine xelatex --variable graphics=yes --variable "geometry:margin=1in"' had status 43 

小心%签署列名称。您需要为文本指定清理函数，以处理 LaTeX 命令，并为列名指定处理百分号。

Use the \cellcolor命令为 LaTeX 表格中的单元格着色。

这是一个 .Rmd 文件示例

---
title: "Colors of xtable cells"
header-includes:
   - \usepackage{longtable}
   - \usepackage[table]{xcolor}
   - \usepackage{colortbl}
output:
    pdf_document
---

Build the example data set

```{r, include = FALSE}
library(xtable)
j <-
  structure(list(Trans = c(89.8, 3337, NA, 97.55, NA, 3558.7, NA, 
  4290.6, NA, 65.95, 94.55, 3495.9), `%CPU` = c(6.938, 79.853, 
  1.875, 4.87, 1.46, 37.885, 1.63, 64.576, 1.165, 3.425, 5.67, 
  33.856), `%Heap Used` = c(9.9, 76.95, 3.77, 9.8, 6.73, 59.23, 
  3.94, 67.38, 3.73, 9.13, 9.57, 62.11), `Heap Usage/MB` = c(263.884, 
  1942.246, 99.104, 257.717, 178.951, 1657.447, 99.933, 2137.134, 
  96.687, 242.024, 256.302, 1646.117)), .Names = c("Trans", "%CPU", 
  "%Heap Used", "Heap Usage/MB"), class = "data.frame", row.names = c(NA, 
  -12L))
```

Create a version of the `data.frame` with red cells for \%CPU greater than 70.
Set the color and round to two digits.

```{r, include = FALSE}
j[, 2] <- ifelse(j[, 2] > 70, paste("\\cellcolor{red}{", round(j[, 2], 2), "}"), round(j[, 2], 2))
```

The resulting table is:

```{r results = "asis"}
print(xtable(j,
             digits = 2,
             row.names = FALSE,
             caption = "JVM Usage"),
      sanitize.text.function = identity,
      sanitize.colnames.function = NULL,
      caption.placement   = "top",
      tabular.environment = "longtable",
      comment = FALSE,
      floating=FALSE) 
```

产生以下输出：