Change the appearance of a single bar in grouped barplot

Question

I'm trying to change the appearance of a specific bar in a grouped barplot with TikZ. But I can't find anywhere how to do what I want to achieve.

Specifically, I have three groups of three bars, where the first one represents something completely different from the other two. I would like to make it appear like the following example that I've made in powerpoint:

Do you have any idea on how to realize this?

EDIT: This is what I've made so far:

\documentclass[10pt,bigtitle,twocolumn,SECTION,absheading]{article}
\usepackage{pgfplots,pgfplotstable}
\usetikzlibrary{pgfplots.groupplots}

\begin{document}

    \begin{figure}[h]
    \pgfplotsset{compat=1.14}
        \pgfplotsset{
            legend image with text/.style={
                legend image code/.code={%
                    \node[anchor=center] at (0.3cm,0cm) {#1};
                }
            },
        }
    \begin{tikzpicture}
        \begin{groupplot}[
            group style={
                group size=1 by 2,
                x descriptions at=edge bottom,
                y descriptions at=edge left,
                vertical sep=1.6mm, % modified
                group name=G % added
            },
            ybar,
            axis lines=left, % added
            enlarge y limits=0,
            enlarge x limits=0.3,
            ylabel={\# trials},
            xtick=data,
            symbolic x coords={gHHT,gATH,gCTR},
            nodes near coords,
            nodes near coords align={vertical},
            every node near coord/.append style={rotate=90, anchor=west},
            legend style={at={(0.93,0.9)}},
        ]
        \nextgroupplot[ymin=0, ymax=50, height=6cm, width=8cm]
            \addplot coordinates {(gHHT,13.67) (gATH,7) (gCTR,13.5)};
            \addplot coordinates {(gHHT,4.67) (gATH,33.6) (gCTR,38)};
        \nextgroupplot[ymin=0, ymax=23, height=6cm, width=8cm]
            \addplot coordinates {(gHHT,16.4) (gATH,12.3) (gCTR,0)};
            \addplot coordinates {(gHHT,7) (gATH,6) (gCTR,0)};
            \legend{\# valid,\# failed} % added
            \addlegendimage{legend image with text=($\cdot$) \; \,}
            \addlegendentry{\# part.}
        \end{groupplot}
    \node [rotate=90] at (G c1r1.east) {\textit{Manual control}}; % added
    \node [rotate=90] at (G c1r2.east) {\textit{Shared control}}; % added
    \node at (1.2,2.4) {(3)};
    \node at (3.2,4) {(3)};
    \node at (5.2,4.25) {(4)};
    \node at (1.2,-0.4) {(5)};
    \node at (3.2,-01.2) {(3)};
    \node at (5.2,-3.8) {(0)};
    \draw (current bounding box.south west) rectangle (current bounding box.north east); % added 
    \end{tikzpicture}
\caption{caption.}
\end{figure}

\end{document}

Answer 1

Do you mean something like the following? If so, please look at the comments in the code for more details on how it works.

% used PGFPlots v1.14
\documentclass[border=5pt]{standalone}
\usepackage{pgfplots,pgfplotstable}
    \usetikzlibrary{pgfplots.groupplots}
    \pgfplotsset{
        % use this `compat' level or higher
        % (it is only needed for the "advanced" positioning of the axis labels)
        compat=1.3,
        % create a style to hold the stuff needed for a `ycomb' in a `ybar'
        % environment
        Ycomb/.style={
            ycomb,
            % because the "bar cycle list" does not contain markers --> add one
            mark=*,
            % apply the "bar shift" also here ...
            xshift=-\pgfplotbarwidth,
            % ... and that needs correction/compensation for the `nodes near coords'
            nodes near coords style={
                yshift=-\pgfplotbarwidth,
            },
            % because also the `nodes near coords' need/have special labels
            % --> allow that here
            point meta=explicit symbolic,
            % unfortunately the above `xshift' also applies to the legend image
            % so this needs to be corrected again
            % --> modified default style to correct/compensate that
            my ybar legend,
        },
        % copied `ybar legend' style from the manual
        % and modified to compensate the needed `xshift' for the `ycomb' plot
        /pgfplots/my ybar legend/.style={
            /pgfplots/legend image code/.code={
                \draw [##1,
                    /tikz/.cd,
                    bar width=3pt,
                    yshift=-0.2em,
                    bar shift=0pt,
                    % compensate `xshift' of `ycomb' plot
                    % (which also is applied to the legend image)
                    xshift=10pt,
                ] plot coordinates {(0cm,0.8em) (2*\pgfplotbarwidth,0.6em)};
            },
        },
        % copied from the manual and modified it, so the shift applies to *all*
        % added plots and not only bar plots
        /pgfplots/bar shift auto/.style={
            /pgf/bar shift={
                % total width = n*w + (n-1)*skip
                % -> subtract half for centering
                -0.5*(\numplots*\pgfplotbarwidth + (\numplots-1)*(#1)) +
                % the '0.5*w' is for centering
                (.5+\plotnum)*\pgfplotbarwidth + \plotnum*(#1)
            },
        },
    }
\begin{document}
    \begin{tikzpicture}
        \begin{groupplot}[
            group style={
                group size=1 by 2,
                x descriptions at=edge bottom,
                y descriptions at=edge left,
                vertical sep=1.6mm,
                group name=G,
            },
            ybar,
            axis lines=left,
            enlarge y limits=0,
            enlarge x limits=0.3,
            ylabel={\# trials},
            xtick=data,
            symbolic x coords={gHHT,gATH,gCTR},
            nodes near coords,
            nodes near coords align={vertical},
            every node near coord/.append style={rotate=90, anchor=west},
            legend style={at={(0.93,0.9)}},
        ]
        \nextgroupplot[ymin=0, ymax=50, height=6cm, width=8cm]
            % copied next `\addplot' command and applied style
            % also added the "custom" labels (shown by the `nodes near coords')
            \addplot+ [Ycomb]
                coordinates {(gHHT,13.67) [(3)] (gATH,7) [(3)] (gCTR,13.5) [(4)]};
            \addplot coordinates {(gHHT,13.67) (gATH,7) (gCTR,13.5)};
            \addplot coordinates {(gHHT,4.67) (gATH,33.6) (gCTR,38)};
        \nextgroupplot[ymin=0, ymax=23, height=6cm, width=8cm]
            % copied next `\addplot' command and applied style
            % also added the "custom" labels (shown by the `nodes near coords')
            \addplot+ [Ycomb]
                coordinates {(gHHT,16.4) [(5)] (gATH,12.3) [(3)] (gCTR,0) [(0)]};
            \addplot coordinates {(gHHT,16.4) (gATH,12.3) (gCTR,0)};
            \addplot coordinates {(gHHT,7) (gATH,6) (gCTR,0)};

            \legend{comb,\# valid,\# failed}
%            % the following two lines caused an error, so I just commented them
%            \addlegendimage{legend image with text=($\cdot$) \; \,}
%            \addlegendentry{\# part.}
        \end{groupplot}

        \node [rotate=90] at (G c1r1.east) {\textit{Manual control}};
        \node [rotate=90] at (G c1r2.east) {\textit{Shared control}};

        % I enlarged the bounding box a bit at the top, so the rectangle doesn't
        % touch the arrow tip of the upper y-axis any more
        % (--> added `yshift')
        \draw (current bounding box.south west)
            rectangle ([yshift=1ex] current bounding box.north east);
    \end{tikzpicture}
\end{document}