pgfplotstable：如何在每列上添加变量名（x_1、x_2、...）？

Question

我想创建一个线性方程组的确使用 pgfplotstable。

如果某些字符串已被替换，我该如何添加变量名称（x_1，x_2，...或其他名称：x，y，z）？

string replace={0}{}, string replace={-1}{-x}, string replace={1}{x}

\documentclass[border=5pt, varwidth]{standalone}
\usepackage{pgfplotstable, systeme}
 \pgfplotsset{compat=1.13}

\pgfplotstableset{
string type,%
%header=false, 
every head row/.style={output empty row},%
column type=r,%
postproc cell content/.append style={
/pgfplots/table/@cell content/.add={$}{$},
},%
}

\begin{document}
\pgfplotstableread{
x                    y
-1                   0
0                    1
1                    2
3                    3 
0                    4
13                  5
-6                   6
-\frac{3}{2}    7
-12                 8
}\test


Actual:  \pgfplotstabletypeset[]{\test} 
%
Partially replaced:  \pgfplotstabletypeset[
string replace={0}{},
string replace={-1}{-x},
string replace={1}{x},
]{\test} \\

\bigskip
Target:  $\newcolumntype{R}{>{{}}r<{{}}}
\setlength\arraycolsep{1pt}
\begin{array}{ r R r R}
-                      &x_1 &    &            \\
{}                    & {} &    &x_2           \\
{}                    &x_1 &+2 &x_2           \\
3                     &x_1 &+3 &x_2           \\
{}                   & {} &+4 &x_2           \\
{}  13             &x_1  &+5 &x_2           \\
- 6                 &x_1 &+6 &x_2           \\
-\frac{3}{2}    &x_1 &+7 &x_2           \\
-12                &x_1 &+8 &x_2           \\
\end{array}$

\end{document}

Answer 1

这只是一个部分解决方案，因为如果数字不是数字而是数学表达式（例如，如果您在-\fraq{...}{...}第二列），我不知道如何处理第二列的符号。

不过，我认为它可能对你有用。

使用\pgfplotstablemodifyeachcolumnelement我etoolbox已经修改了列值：

\documentclass[border=5pt, varwidth]{standalone}
\usepackage{etoolbox}
\usepackage{pgfplotstable, systeme}
\pgfplotsset{compat=1.13}

\pgfplotstableset{
string type, 
every head row/.style={output empty row},
column type=r,%
%postproc cell content/.append style={
%/pgfplots/table/@cell content/.add={$}{$},
%},%
}

\begin{document}
\pgfplotstableread{
x                    y
-1                   0
0                    1
1                    2
3                    3 
0                    4
13                  5
-6                   6
-\frac{3}{2}    7
-12                 8
}\test

\newcommand{\firstvar}{x_1}
\newcommand{\secondvar}{x_2}
\pgfplotstablemodifyeachcolumnelement{x}\of\test\as\cell{%
\edef\cell{% code from https://tex.stackexchange.com/questions/24922/comparing-an-argument-to-a-string-when-argument-is-a-result-of-a-command-with-et
 \expandafter\ifstrequal\expandafter{\cell}{0}{}{\expandafter\ifstrequal\expandafter{%
        \cell}{-1}{$-\firstvar$}{%
        \expandafter\ifstrequal\expandafter{\cell}{1}{$\firstvar$}{$\cell\firstvar$}%
}}}
}
\pgfplotstablemodifyeachcolumnelement{y}\of\test\as\cell{%
\edef\cell{% this part is to improve to correctly manage the negative value
 \expandafter\ifstrequal\expandafter{\cell}{0}{}{\expandafter\ifstrequal\expandafter{%
        \cell}{-1}{$-\secondvar$}{%
        \expandafter\ifstrequal\expandafter{\cell}{1}{$+\secondvar$}{$+\cell\secondvar$}%
}}}
}
\pgfplotstabletypeset{\test}
\end{document}