Place values from table centred within bars in a stacked bar chart

Question

I would like to get the values from the the columns Cd, Cr, and Ni showing on their respective sections of the bars in the chart. I would like them to be aligned in the center of each section. I have used nodes near coords and \addplot with coordinates to show the values. The first three fit within the correct place but they are not centered. Furthermore, the subsequent \addplot show up in the wrong position. Could I get some help with this issue? Thank you in advance for the help.

Code is

\documentclass[border={0pt,0pt,0pt,0pt}]{standalone}

\usepackage{helvet}
\usepackage[eulergreek]{sansmath}
\usepackage{tikz,pgfplotstable}
\usetikzlibrary{patterns}
\pgfplotsset{compat=1.8,
 every axis/.style={axis on top},
 tick label style = {font=\sansmath\sffamily\small\itshape,xshift={-15}},
 every axis label = {font=\sansmath\sffamily},
 legend style = {font=\sansmath\sffamily},
 label style = {font=\sansmath\sffamily}, 
 }
\begin{document}

\pgfplotstableread{
Species                         Cd      Cr      Ni
V.\space c.\space cochiensis    3.67    2.16    2.27
L.\space teres                  2.76    0       0
L.\space s.\space claibornensis 2.52    0       1.94
A.\space pectorosa              2.34    0       1.34
L.\space subviridis             2.34    0       0
U.\space imbecillis             2.26    0.76    1.44
V.\space vibex                  2.21    0       1.58
C.\space fluminalis             1.39    0       0
P.\space casertanum             1.17    0       0
P.\space compressum             1.08    0       0
C.\space rhizophorae            0.40    0       0
P.\space favidens               0.24    0       0
L.\space marginalis             0.10    0       0
M.\space nervosa                0       1.08    1.82
R.\space cuneata                0       0.90    0
A.\space plicata                0       0.85    1.69
L.\space siliquoidea            0       0.80    1.42
M.\space falcata                0       0.42    1.63
H.\space perovalis              0       0       1.56
V.\space nebulosa               0       0       1.35
H.\space cumingii               0       -0.81   0
D.\space chilensis              0       -1.09   0
}\testdata

\begin{tikzpicture}
\begin{axis}[
            xbar stacked,
            xmin=-3,
            xmax=8,         
            xticklabel style=transparent,    
            xtick style=transparent,
            ytick style=transparent,            
            axis y line*=middle,
            every inner y axis line/.append style = {dotted, ultra thick},
            height=11cm,
            width=11.9cm,           
            enlarge y limits={abs=0.725},
            enlarge x limits={abs=0.725},            
            xlabel={RS = $\log (LC_{50\textit{Lf}}/LC_{50\textit{i}})$},             
            ytick=\empty,
            legend style={at={(0.8,0.6)},anchor=north west, draw=none},            
            nodes near coords,
            visualization depends on=x\as\myx,          
            nodes near coords align={center},
            every node near coord/.append style={anchor ={180-sign(\myx)*180},font=\footnotesize},
            point meta = explicit symbolic         
]
\addlegendimage{empty legend},
\addplot [fill=black!90!black!45] table [x=Cr, y expr=\coordindex] {\testdata};   % "First" column against the data index
\addplot [fill=black!90!black!20] table [x=Cd, y expr=\coordindex] {\testdata};
\addplot [fill=black!5] table [x=Ni, y expr=\coordindex] {\testdata};
\addplot [only marks,mark size=0pt,point meta=explicit symbolic,
    nodes near coords,nodes near coords style={anchor=east,font =\small\itshape}] 
    table[x expr={-1*ifthenelse(\thisrow{Cd}+\thisrow{Cr}+\thisrow{Ni}>0,
        \thisrow{Cd}+\thisrow{Cr}+\thisrow{Ni},0)},y expr=\coordindex,meta=Species]  {\testdata};
\addplot[black] coordinates{(2.16,0)[2.16]};%shows up well but not 'center'.
\addplot[black] coordinates{(3.67,0)[3.67]};%shows up well but not 'center'.
\addplot[black] coordinates{(2.27,0)[2.27]};%shows up well but not 'center'.
%
%all other \addplot entries from table.
%
\addplot[black] coordinates{(0,20)};
\addplot[black] coordinates{(-0.81,20)[-0.81]};%shows up on the wrong position. 
\addplot[black] coordinates{(0,20)};
\addplot[black] coordinates{(0,21)};
\addplot[black] coordinates{(-1.09,21)[-1.09]};%shows up on the wrong position.
\addplot[black] coordinates{(0,21)};


\addlegendentry{\hspace{-0.85cm}\textbf\small{Metals}},
\addlegendentry{Cr(VI)},
\addlegendentry{Cd(II)},
\addlegendentry{Ni(II)},
\end{axis}
\end{tikzpicture}

\end{document}

Answer 1

Out of the two points you raise I think one of them can be addressed rather easily. The issue is that these are stacked plots. However, it seems that you only want to show the x values. Then you seem to want to suppress the nodes if the bar is too small. This can be achieved with a style

\pgfplotsset{my meta/.style={point meta=\thisrow{#1},
every node near coord/.append style={%
 opacity={ifthenelse(abs(\csname my#1\endcsname)><threshold>,1,0)}}}}

where <threshold> is taken to be 0.5 in the below example. For the horizontal centering I use a variant of this solution.

\documentclass[border={0pt,0pt,0pt,0pt}]{standalone}

\usepackage{helvet}
\usepackage[eulergreek]{sansmath}
\usepackage{tikz,pgfplotstable}
\usetikzlibrary{patterns}
\pgfplotsset{compat=1.8,
 every axis/.style={axis on top},
 tick label style = {font=\sansmath\sffamily\small\itshape,xshift={-15}},
 every axis label = {font=\sansmath\sffamily},
 legend style = {font=\sansmath\sffamily},
 label style = {font=\sansmath\sffamily}, 
 }
\makeatletter
\pgfplotsset{
    calculate offset/.code={
        \pgfkeys{/pgf/fpu=true,/pgf/fpu/output format=fixed}    
        \pgfmathsetmacro\testmacro{(10^\pgfplots@data@scale@trafo@EXPONENT@x)*%
         \csname my#1\endcsname/2*\pgfplots@x@veclength)}
        \pgfkeys{/pgf/fpu=false}
        },
    nodes near coords horizontally centered/.style={
        every node near coord/.append style={
            /pgfplots/calculate offset=#1,
            xshift=-\testmacro
        },
    }
}
\makeatother 

\begin{document}

\pgfplotstableread{
Species                         Cd      Cr      Ni
V.\space c.\space cochiensis    3.67    2.16    2.27
L.\space teres                  2.76    0       0
L.\space s.\space claibornensis 2.52    0       1.94
A.\space pectorosa              2.34    0       1.34
L.\space subviridis             2.34    0       0
U.\space imbecillis             2.26    0.76    1.44
V.\space vibex                  2.21    0       1.58
C.\space fluminalis             1.39    0       0
P.\space casertanum             1.17    0       0
P.\space compressum             1.08    0       0
C.\space rhizophorae            0.40    0       0
P.\space favidens               0.24    0       0
L.\space marginalis             0.10    0       0
M.\space nervosa                0       1.08    1.82
R.\space cuneata                0       0.90    0
A.\space plicata                0       0.85    1.69
L.\space siliquoidea            0       0.80    1.42
M.\space falcata                0       0.42    1.63
H.\space perovalis              0       0       1.56
V.\space nebulosa               0       0       1.35
H.\space cumingii               0       -0.81   0
D.\space chilensis              0       -1.09   0
}\testdata

\begin{tikzpicture}
\pgfplotsset{my meta/.style={point meta=\thisrow{#1},
nodes near coords horizontally centered=#1,
every node near coord/.append style={%
opacity={ifthenelse(abs(\csname my#1\endcsname)>0.5,1,0)}}}}
\begin{axis}[
            xbar stacked,
            xmin=-3,
            xmax=8,         
            xticklabel style=transparent,    
            xtick style=transparent,
            ytick style=transparent,            
            axis y line*=middle,
            every inner y axis line/.append style = {dotted, ultra thick},
            height=11cm,
            width=11.9cm,           
            enlarge y limits={abs=0.725},
            enlarge x limits={abs=0.725},            
            xlabel={RS = $\log (LC_{50\textit{Lf}}/LC_{50\textit{i}})$},             
            ytick=\empty,
            legend style={at={(0.8,0.6)},anchor=north west, draw=none},            
            nodes near coords,
            visualization depends on=x\as\myx, 
            visualization depends on=\thisrow{Cr}\as\myCr,
            visualization depends on=\thisrow{Cd}\as\myCd,
            visualization depends on=\thisrow{Ni}\as\myNi,         
            nodes near coords align={center},
            every node near coord/.append style={%anchor={180-sign(\myx)*180},
            font=\tiny},
]
\addlegendimage{empty legend},
\addplot [fill=black!90!black!45,my meta=Cr] table [x=Cr, y expr=\coordindex] {\testdata};   % "First" column against the data index
\addplot [fill=black!90!black!20,my meta=Cd] table [x=Cd, y expr=\coordindex] {\testdata};
\addplot [fill=black!5,my meta=Ni] table [x=Ni, y expr=\coordindex] {\testdata};
\addplot [only marks,mark size=0pt,point meta=explicit symbolic,
    nodes near coords,nodes near coords style={anchor=east,font=\small\itshape,opacity=1}] 
    table[x expr={-1*ifthenelse(\thisrow{Cd}+\thisrow{Cr}+\thisrow{Ni}>0,
        \thisrow{Cd}+\thisrow{Cr}+\thisrow{Ni},0)},y expr=\coordindex,meta=Species]  {\testdata};
\addlegendentry{\hspace{-0.85cm}\textbf\small{Metals}},
\addlegendentry{Cr(VI)},
\addlegendentry{Cd(II)},
\addlegendentry{Ni(II)},
\end{axis}
\end{tikzpicture}

\end{document}