KnitR，Latex條件顯示文本和代碼塊

Question

如何根據某些條件打開/關閉特定部分的顯示？ 例如，我想僅在xyplotFacSpecTotVarTest.pdf存在時顯示以下子部分。

我該怎么做 ？

\subsection{Checksum: Factor, Specific, and Total Variance}
Perhaps the most basic test of a regression model is if the factor and specific variances sum to equal the total variance.  Here, we 
present this diagnostic as an xy-plot, with the sum of factor and specific variance on the x-axis and the total variance on the y-axis.  We 
expect the plotted points to line up tightly along the identity line.

\clearpage
\begin{figure}[!h]

\centering

\includegraphics{\Sexpr{image_dir}xyplotFacSpecTotVarTest.pdf}

\caption{Total Variance vs. Sum of Factor and Specific Variance, All Instruments Passing Exposure Model.}

\end{figure}

Answer 1

將您的子部分放在另一個文件中，例如sub.Rnw 。 然后有條件地將它包含在主文檔中，例如

<<child = if (file.exists('foo.pdf')) 'sub.Rnw'>>=
@