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如果条件不满足，则使 itemize 中的项目消失

tag-icon • tag-icon conditionals itemize
如果条件不满足，则使 itemize 中的项目消失

以下是 MWE：

\documentclass{article}
\newcommand{\VarOne}{1500}
\begin{document}
I want this list to have item Two if VarOne is more than 1000. If it is not, this will be a two item list. By the way, I could not    get this to print VarOne with a backslash!                                                                                            
\begin{itemize}
  \item One 
  \item Two only if VarOne is more than 1000. 
  \item Three
\end{itemize}
\end{document}

我如何实现这个目标？

答案1

Ulrike Fischer 给出了关于查询的提示low-level \ifnum，此版本使用了包\ifnumgreater中的宏etoolbox（并提供了比较）。

在我看来，\VarOne只要只涉及整数值，就不应该将其用作宏而应该用作计数器。

\documentclass{article}
\newcommand{\VarOne}{1500}


\usepackage{etoolbox}%
\begin{document}
I want this list to have item Two if VarOne is more than 1000. If it is not, this will be a two item list. By the way, I could not    get this to print \(\backslash\)VarOne with a backslash!                                                                                            
\begin{itemize}
  \item One
  \ifnumgreater{\VarOne}{1000}{\item Two only if VarOne is more than 1000.}{}
  \item Three
\end{itemize}

\renewcommand{\VarOne}{100}%
Once again -- without the 2nd argument
\begin{itemize}
  \item One 
  \ifnumgreater{\VarOne}{1000}{\item Two only if VarOne is more than 1000.}{}
  \item Three
\end{itemize}


\end{document}

在此处输入图片描述

答案2

这是您的请求的轻度自动化版本，使用了一些来自enumerate自动对环境中的物品进行排序：

在此处输入图片描述

\documentclass{article}
\usepackage{environ,etoolbox,multido}

% Taken from https://tex.stackexchange.com/a/128318/5764
\makeatletter
\newcounter{varoneitem}\newcounter{listcount}[varoneitem]
\let\olditem\item% Store regular \item macro
\NewEnviron{varoneitem}[1][0]{%
  \stepcounter{varoneitem}% New orderenum environment (also resets listcount)
  \g@addto@macro{\BODY}{\item\relax\item}% Used to delimit the items; last item identified by \item\relax\item
  \def\item##1\item{% Redefine \item to capture contents
    \def\itemarg{##1}%
    \expandafter\ifx\itemarg\relax\else% Last item not reached
      \stepcounter{listcount}% Next item being processed
      \csgdef{varoneitem@\thevaroneitem @\thelistcount}{##1}% Store item in control sequence
      \expandafter\item% Recursively continue processing items
    \fi
  }
  \BODY% Process environment (save items)
  \begin{itemize}
    \multido{\i=1+1}{\value{listcount}}{%
      \ifnum\i=#1\relax
        \ifnum\VarOneCondition\relax
          \olditem \csname varoneitem@\thevaroneitem @\i\endcsname
        \fi
      \else
        \olditem \csname varoneitem@\thevaroneitem @\i\endcsname
      \fi
    }
  \end{itemize}
}
\makeatother

\newcommand{\VarOne}{1500}
\newcommand{\VarOneCondition}{\VarOne>1000}

\begin{document}

I want this list to have item Two if \verb|\VarOne| is more than 1\,000. If it is not, this will be a two item list. 
By the way, I could not get this to print \verb|\VarOne| with a backslash!                                                                                            

\begin{varoneitem}[2]
  \item One 
  \item Two only if \texttt{\string\VarOne} is more than 1\,000.
  \item Three
\end{varoneitem}

\renewcommand{\VarOne}{900}
\begin{varoneitem}[2]
  \item One 
  \item Two only if \texttt{\string\VarOne} is more than 1\,000.
  \item Three
\end{varoneitem}


\end{document}

这个想法是处理列表两次。在第一次迭代中，所有\items 都被收集并存储在宏中。在第二次迭代中，根据 有条件地输出项目\VarOneCondition。

由于该过程\item在宏中“捕获”每个内容，因此逐字内容应以不同的方式传递。我在上面的例子中也展示了这一点。

新创建的varoneitem环境采用可选参数，该参数标识有条件抑制的项目编号。其他改进也是可能的，但我不确定您的最终用例是什么。

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