pgfplots, plot options ignored when using "restrict expr to domain"

Question

This is my first post here. I want to use pgfplots (wonderful piece of software/code) to display some data (A,B,C) from a experiment. In some diagrams I want to plot x=A and y=B but only for some points that are within a speficic C-range.

This can be done useing

restrict expr to domain

In one case all the plot options are ingored if I use this feature. See the example (myData2.csv). When I use slightly different data (myData and myData3) it works. I really tried all that is in my power but I do not solve this mystery.

In the example below I have three plots all with the same options. Bur only in two cases this options are considered correctly.

Where is my mistake?

\documentclass{standalone}  
\usepackage{pgfplots} 
\pgfplotsset{compat=newest}   

\usepackage{filecontents}  

\begin{filecontents}{myData.csv} 
A;B;C
0.02;20;2
0.03;20;2
0.00;20;3
0.03;20;3
\end{filecontents}  

\begin{filecontents}{myData2.csv}
A;B;C 
0.02;1;40
0.02;2;40
0.02;3;40
0.02;4;40
0.02;5;40
0.01;0;40
0.01;1;40
0.3;2;40
0.3;3;40
0.01;4;40
0.01;5;40
\end{filecontents} 

\begin{filecontents}{myData3.csv} 
A;B;C
0.02;2;20
0.03;2;20
0.1;3;20
0.2;3;20
\end{filecontents} 

\begin{document}

\begin{tikzpicture}
\begin{axis}[
xlabel={xlabel},
ylabel={ylabel},
xmin=0,
xmax=0.3,
ymin=0,
ymax=100,
width =100mm,
height = 70mm,
]
\addplot
    [
    % Optionen  
    mark=*, 
    draw=red,
    line width=1.5pt    
    ]
    table
    [   
    x=A,
    y=B,
    col sep=semicolon,
    row sep = newline,
    restrict expr to domain={\thisrow{C}}{2.1:3.1}, 
    ] {myData.csv};
    \addlegendentry{C = 3, file myData} 
\addplot
    [
    % Optionen  
    mark=*, 
    draw=red,
    line width=1.5pt    
    ]
    table
    [   
    x=A,
    y=C,
    col sep=semicolon,
    row sep = newline,
    restrict expr to domain={\thisrow{B}}{2.1:3.1}, 
    ] {myData3.csv};
    \addlegendentry{B = 3, file myData3}        
\addplot
    [
    % Optionen
    mark=*, 
    draw=red,
    line width=0.5pt
    ]
    table
    [   
    x=A,
    y=C,
    col sep=semicolon,
    row sep = newline,
    restrict expr to domain={\thisrow{B}}{2.1:3.1}, 
    ] {myData2.csv};
    \addlegendentry{B = 3, file myData2}    
\end{axis}  
\end{tikzpicture}

\end{document}

Solution

\documentclass{standalone}  
\usepackage{pgfplots} 
\pgfplotsset{compat=newest}   

\usepackage{filecontents}  

\begin{filecontents}{myData2.csv}
A;B;C 
0.0;3;40
0.0;2;40
0.1;3;40
0.1;2;40
0.2;3;40
0.2;2;40
0.3;3;40
0.3;2;40
0.4;3;40
0.4;2;40
\end{filecontents} 

\begin{document}

\begin{tikzpicture}
\begin{axis}[
xlabel={xlabel},
ylabel={ylabel},
xmin=0,
xmax=0.3,
ymin=0,
ymax=100,
width =100mm,
height = 70mm,
]      
\addplot
    [
    % Optionen
    mark=*, 
    draw=blue,
    line width=0.5pt
    ]
    table
    [   
    x=A,
    y=C,
    col sep=semicolon,
    row sep = newline,
    restrict expr to domain={\thisrow{B}}{2.1:3.1}, 
    unbounded coords=discard % <-- important
    ] {myData2.csv};
    \addlegendentry{correct (points connected, using \texttt{unbounded coords=discard})}
\addplot
    [
    % Optionen
    mark=o, 
    draw=red,
    line width=1.5pt
    ]
    table
    [   
    x=A,
    y=C,
    col sep=semicolon,
    row sep = newline,
    restrict expr to domain={\thisrow{B}}{2.1:3.1}, 
    %unbounded coords=discard % <-- important
    ] {myData2.csv};
    \addlegendentry{not correct (points not connected)}        
\end{axis}  
\end{tikzpicture}

\end{document}

Answer 1

As percusse and user14649 pointed out, the problem stems from the fact that only two coordinates are left after the filtering, and no connecting line is drawn.

To fix this, you should set the key unbounded coords=discard, which will treat the plot as if the filtered out coordinates had never been there in the first place. The default behaviour is jump, which interrupts the plot when a coordinate is discarded.

Here's a slightly simpler example to explain how these keys work. If you don't apply any filters, a plot might look like this:

If you only want to use the coordinates where C is 1, you can use restrict expr to domain={\thisrow{C}}{0.5:1.5}, leading to

To get a connected plot, you also have to set unbounded coords=discard:

If you had set restrict expr to domain*={\thisrow{C}}{0.5:1.5} (with an asterisk), all x-coordinates where the value of C is greater than 1.5 would have been set to 1.5:

\documentclass[border=5mm]{standalone}  
\usepackage{pgfplots} 

\usepackage{filecontents}  


\begin{filecontents}{myData2.csv}
A;B;C 
1;10;1
2;20;1
3;30;2
4;20;1
5;10;2
\end{filecontents} 

\begin{document}

\begin{tikzpicture}
\begin{axis}[xmin=1,xmax=5,ymin=0]
\addplot[
        mark=*, 
        red,
        line width=0.5pt
    ]
    table
    [   
        x=A,
        y=B,
        col sep=semicolon
    ] {myData2.csv};  
\end{axis}  
\end{tikzpicture}

\end{document}