Legend Entry Y-Shifted Along with Plot

Question

I am using pgfplots for crystallographic data analysis. I can effectively use yshift to shift plots within the axis environment, however, the legend entry line reference also shifts. I originally intended to use pgfplotstable to simply add or subtract from every data point to shift but this was computationally intensive (many data points). Excuse the constant plot hack to have a drop-down plot. Representative Code (courtesy of commenter):

\documentclass{standalone}
\usepackage{pgfplots}
\usepackage{pgfplotstable}
\pgfplotsset{compat = 1.13}
\pgfplotstableset{col sep = comma}

\begin{document}
\pgfplotstableread{
20, 1000
70, 500
}{\data}

\begin{tikzpicture}
\begin{axis}

\addplot[black] table[x index = 0, y index = 1, col sep = comma] {\data};
\addlegendentry[]{040\_Mn}
\addplot[red!20!blue] table[x index = 0, y expr={\thisrowno{1} - 500}] {\data};
\addlegendentry[]{023\_Mn}
\addplot[yshift=-2cm,red!20!blue] table[x index = 0, y index=1] {\data};
\addlegendentry[]{035\_Mn}
\addplot[yshift = -5cm, red!30!blue] expression {x^2};
\end{axis}
\end{tikzpicture}
\end{document}

Answer 1

Here are two options. First, instead of yshift, use something like

\addplot[red!20!blue] table[x index = 0, y expr={\thisrowno{1} - 500}] {\data};

This subtracts 500 from the y-value in the table. You can use the name of a text file instead of loading into a macro (here \data) first.

Another option is to use yshift, but add forget plot to the \addplot options. forget plot disables adding the plot to the legend, so you need \addlegendimage{<style options for plot>} instead.

\documentclass{standalone}
\usepackage{pgfplots}
\usepackage{pgfplotstable}
\pgfplotsset{compat = 1.13}
\pgfplotstableread[col sep=comma]{
20, 1000
70, 500
}{\data}

\begin{document}
\begin{tikzpicture}
\begin{axis}

\addplot[black] table[x index = 0, y index = 1] {\data};
\addlegendentry[]{040\_Mn}
\addplot[red!20!blue] table[x index = 0, y expr={\thisrowno{1} - 500}] {\data};
\addlegendentry[]{023\_Mn}
\addplot[yshift=-2cm,green,forget plot] table[x index = 0, y index=1] {\data};
\addlegendimage{green}
\addlegendentry{shifted}
\end{axis}
\end{tikzpicture}

\end{document}