Como mostrar os valores negativos de gráficos de barras agrupados com linha zero em um único gráfico?

Question

I am new to tikz and pgf plots. I want to draw a bar chart with a mixed positive and negative values. 
I want to display all the values (both positive and negative) in a single figure with single axis. 
It means the values greater than 0 and less than 0 in the y-axis need to be displayed in the same figure itself. I have tried but the negative values is not displayed in the bar chart. 
The MWE is as follows.    
\documentclass[10pt,a4paper,twoside]{article}
\usepackage[usenames,dvipsnames]{xcolor}
\usepackage{pgfplots}
\usepackage{textcomp}
\usepackage{subcaption} 
\usepackage{caption}
\usepackage{latexsym}
\pgfplotsset{compat=1.3}
\usepackage[justification=raggedright]{caption}
\pgfplotsset{
bar group size/.style 2 args={
    /pgf/bar shift={%
        -0.5*(#2*\pgfplotbarwidth + (#2-1)*\pgfkeysvalueof{/pgfplots/bar group skip})  + 
        (.5+#1)*\pgfplotbarwidth + #1*\pgfkeysvalueof{/pgfplots/bar group skip}},%
},
bar group skip/.initial=2pt,
plot 0/.style={blue,fill=blue!30!white,mark=none},%
plot 1/.style={red,fill=red!30!white,mark=none},%
plot 2/.style={brown!60!black,fill=brown!30!white,mark=none},%
}

\begin{document}
\begin{figure}
\small
\centering
\begin{tikzpicture}
\centering
\begin{axis}[
ybar,
width=11cm,
height=8cm,
legend style={area legend, at={(0.55,1)},
anchor=north,legend columns=-1},
xtick=data,
symbolic x coords={N \textrightarrow N+T, S \textrightarrow S+T, P \textrightarrow P+T, E \textrightarrow E+T, H \textrightarrow H+T, W\_H \textrightarrow W\_H+T},
x tick label style ={rotate=45, anchor=east, align=right,text width=2.6cm},
xlabel={Models},
enlarge x limits=0.15,
tick label style={},
ylabel={Percentage difference at nDCG@1},
every axis y label/.style={rotate=90,at={(-0.12,0.5)}},
bar width=5pt,
]
\addplot[ybar,black,fill=blue] coordinates {(N \textrightarrow N+T,100) (S \textrightarrow S+T,200) (P \textrightarrow P+T,-120) (E \textrightarrow E+T,150) (H \textrightarrow H+T,155) (W\_H \textrightarrow W\_H+T,267)};

\addplot[ybar,black,fill=pink] coordinates {(N \textrightarrow N+T,100) (S \textrightarrow S+T,-200) (P \textrightarrow P+T,200) (E \textrightarrow E+T,388) (H \textrightarrow H+T,155) (W\_H \textrightarrow W\_H+T,-267)};

\addplot[ybar,black,fill=violet] coordinates {(N \textrightarrow N+T,100) (S \textrightarrow S+T,-200) (P \textrightarrow P+T,-200) (E \textrightarrow E+T,388) (H \textrightarrow H+T,155) (W\_H \textrightarrow W\_H+T,267)};

\legend{\footnotesize TF-IDF,\footnotesize BM25,\footnotesize PL2}
\end{axis}
\end{tikzpicture}
\captionsetup{width=.95\textwidth}
\caption{Performance differences with transliteration.}
\label{isffig14}
\end{figure}
\end{document}

Answer 1

Só para evitar alguns mal-entendidos: Este é o resultado que obtenho usando seu código e acabei de adicionar a linha em y=0.

% used PGFPlots v1.15
\documentclass[border=5pt]{standalone}
\usepackage{pgfplots}
    \pgfplotsset{compat=1.3}
\begin{document}
\small
\begin{tikzpicture}
    \begin{axis}[
        ybar,
        width=11cm,
        height=8cm,
        legend style={
            area legend,
            at={(0.55,1)},
            anchor=north,
            legend columns=-1,
            font=\footnotesize,     % <-- moved here from each legend entry
        },
        xtick=data,
        symbolic x coords={
            N \textrightarrow N+T,
            S \textrightarrow S+T,
            P \textrightarrow P+T,
            E \textrightarrow E+T,
            H \textrightarrow H+T,
            W\_H \textrightarrow W\_H+T
        },
        x tick label style={
            rotate=45,
            anchor=east,
            align=right,
            text width=2.6cm,
        },
        xlabel={Models},
        ylabel={Percentage difference at nDCG@1},
        bar width=5pt,
    ]
        \addplot [black,fill=blue] coordinates {
            (N \textrightarrow N+T,100)
            (S \textrightarrow S+T,200)
            (P \textrightarrow P+T,-120)
            (E \textrightarrow E+T,150)
            (H \textrightarrow H+T,155)
            (W\_H \textrightarrow W\_H+T,267)
        };
        \addplot [black,fill=pink] coordinates {
            (N \textrightarrow N+T,100)
            (S \textrightarrow S+T,-200)
            (P \textrightarrow P+T,200)
            (E \textrightarrow E+T,388)
            (H \textrightarrow H+T,155)
            (W\_H \textrightarrow W\_H+T,-267)
        };
        \addplot [black,fill=violet] coordinates {
            (N \textrightarrow N+T,100)
            (S \textrightarrow S+T,-200)
            (P \textrightarrow P+T,-200)
            (E \textrightarrow E+T,388)
            (H \textrightarrow H+T,155)
            (W\_H \textrightarrow W\_H+T,267)
        };

        % ---------------------------------------------------------------
        % draw a line at $y = 0$
        \draw (axis cs:{[normalized]\pgfkeysvalueof{/pgfplots/xmin}},0)
            -- (axis cs:{[normalized]\pgfkeysvalueof{/pgfplots/xmax}},0);
        % ---------------------------------------------------------------

        \legend{
            TF-IDF,
            BM25,
            PL2,
        }
    \end{axis}
\end{tikzpicture}
\end{document}