plotting a line in a barchart

Question

Problem: line stops at given coordinates, ymax is not obeyed.

\documentclass[a4paper,10pt]{report}
\usepackage[left=1.5cm,top=2cm,right=1.5cm,bottom=1.5cm]{geometry}
\usepackage[table,usenames,dvipsnames]{xcolor}
\usepackage{tikz}
\usepackage{pgfplots}

\pgfplotsset{
    width=\textwidth,
}
\begin{document}
\begin{tikzpicture}
\begin{axis}[
ybar,ymax=100,enlarge y limits={upper,value=1},
height=8cm,
enlargelimits=0.25,
ylabel={Uptime \%},
symbolic x coords={Mar '12,Apr '12,May '12},
xtick=data,
nodes near coords=\rotatebox{90}{\scriptsize\pgfmathprintnumber\pgfplotspointmeta},
]
\addplot[draw=blue,fill=blue!40!white] coordinates      {(Mar '12,100)      (Apr '12,100)       (May '12,100)}; 
\addplot[draw=Salmon,fill=Salmon!40!white] coordinates      {(Mar '12,100)      (Apr '12,100)       (May '12,100)}; 
\addplot[draw=yellow,fill=yellow!40!white] coordinates      {(Mar '12,99.86)    (Apr '12,99.47)     (May '12,99.37)}; 
\addplot[draw=RawSienna,fill=RawSienna!40!white] coordinates    {(Mar '12,100)      (Apr '12,100)       (May '12,99.98)};
\addplot[draw=purple,fill=purple!40!white] coordinates      {(Mar '12,99.69)    (Apr '12,98.79)     (May '12,97.91)}; 
\addplot[draw=cyan,fill=cyan!40!white] coordinates      {(Mar '12,100)      (Apr '12,100)       (May '12,100)}; 
\addplot[draw=magenta,fill=magenta!40!white] coordinates    {(Mar '12,100)      (Apr '12,100)       (May '12,99.96)}; 
\addplot[draw=LimeGreen,fill=LimeGreen!40!white] coordinates    {(Mar '12,100)      (Apr '12,100)       (May '12,99.99)}; 
\addplot[draw=red,fill=red!40!white] coordinates        {(Mar '12,100)      (Apr '12,100)       (May '12,99.99)}; 
\addplot[red,sharp plot] coordinates {(Mar '12,98) (May '12,98)} node[above] at (axis cs:Apr '12,98) {KPI};

\end{axis}
\end{tikzpicture}

\end{document}

Now I like to have a continuous line at 98% without the labels but with the KPI label, and the y axis should stop at 100. Is this possible?

Answer 1

You can adapt the solution from How can I add a zero line to a plot? to add the red line:

\draw [red] ({rel axis cs:0,0}|-{axis cs:May '12,98}) -- ({rel axis cs:1,0}|-{axis cs:May '12,98}) node [pos=0.33, above] {KPI};

will draw a red line across the whole plot width with a label at one third of the length. Note that the x coordinate May '12 isn't actually used for anything here, but you still need to supply a valid value.

The reason your ymax isn't obeyed is that you're calling enlargelimits=0.25, which overrides the ymax. Also, you're setting enlarge y limits={upper,value=1}, which also increases the upper y limit. Replace those options with enlarge x limits=0.25, and your upper y limit will be obeyed. In that case, you'll probably want to set x axis lines*=left, so only the bottom x axis line will be drawn (the * switches off the arrow tip that would otherwise be used).

\documentclass[a4paper,10pt]{report}
\usepackage[left=1.5cm,top=2cm,right=1.5cm,bottom=1.5cm]{geometry}
\usepackage[table,usenames,dvipsnames]{xcolor}
\usepackage{tikz}
\usepackage{pgfplots}

\pgfplotsset{
    width=\textwidth,
}
\begin{document}
\begin{tikzpicture}
\begin{axis}[
ybar,ymax=100,
height=8cm,
enlarge x limits=0.25,
axis x line*=left,
ylabel={Uptime \%},
symbolic x coords={Mar '12,Apr '12,May '12},
xtick=data,
nodes near coords=\rotatebox{90}{\scriptsize\pgfmathprintnumber\pgfplotspointmeta},
]
\addplot[draw=blue,fill=blue!40!white] coordinates      {(Mar '12,100)      (Apr '12,100)       (May '12,100)}; 
\addplot[draw=Salmon,fill=Salmon!40!white] coordinates      {(Mar '12,100)      (Apr '12,100)       (May '12,100)}; 
\addplot[draw=yellow,fill=yellow!40!white] coordinates      {(Mar '12,99.86)    (Apr '12,99.47)     (May '12,99.37)}; 
\addplot[draw=RawSienna,fill=RawSienna!40!white] coordinates    {(Mar '12,100)      (Apr '12,100)       (May '12,99.98)};
\addplot[draw=purple,fill=purple!40!white] coordinates      {(Mar '12,99.69)    (Apr '12,98.79)     (May '12,97.91)}; 
\addplot[draw=cyan,fill=cyan!40!white] coordinates      {(Mar '12,100)      (Apr '12,100)       (May '12,100)}; 
\addplot[draw=magenta,fill=magenta!40!white] coordinates    {(Mar '12,100)      (Apr '12,100)       (May '12,99.96)}; 
\addplot[draw=LimeGreen,fill=LimeGreen!40!white] coordinates    {(Mar '12,100)      (Apr '12,100)       (May '12,99.99)}; 
\addplot[draw=red,fill=red!40!white] coordinates        {(Mar '12,100)      (Apr '12,100)       (May '12,99.99)};
\draw [red] ({rel axis cs:0,0}|-{axis cs:May '12,98}) -- ({rel axis cs:1,0}|-{axis cs:May '12,98}) node [pos=0.33, above] {KPI};
\end{axis}
\end{tikzpicture}

\end{document}