pgfplot: equidistant bars, different colours for groups

Question

I have a document like this:

\documentclass{article}

\usepackage{tikz,pgfplots}
\usepackage{pgfplotstable}

\begin{filecontents}{data.csv}
Thing;Weight
Dog 1;50
Dog 2;45
Cat 1;10
Cat 2;10
Cat 3;11
Parrot;3
\end{filecontents}

\begin{document}

\pgfplotstableread[col sep=semicolon]{data.csv}{\table}

\begin{tikzpicture}%
    \begin{axis}[%
        ybar=3mm,%
        xtick=data,%
        xticklabels from table={\table}{Thing},%
        x tick label style={rotate=60},%
        nodes near coords%
    ]%
        \addplot table [x expr=\coordindex,y index=1,col sep=semicolon] {\table};%
    \end{axis}
\end{tikzpicture}

\end{document}

Now, I would like to have the two dog bars in one colour, the three cat bars in a different colour and so on. The bars should be equidistant.

I know, each addplot gets its own colour. I would have to make one plot for each group (animal/thing). But pgfplots uses only the first plot for the xticklabels. I could make one table containing all groups with all y values set to 0 and have nodes near coords only plotted if the y value isn’t 0, and then for each group a seperate table with the actual data. But that is a rather ugly hack, as it plots plots over an effectively invisible plot (with bar shift = 0). Is there an elegant way to group bars using colours (not vertical spaces)?

From all I found here on TSX, for my actual document I tinkered this hack:

\documentclass{article}

\usepackage{tikz,pgfplots}
\usepackage{pgfplotstable}
\usepackage{ifthen}

\pgfplotsset{compat=1.16}

\begin{filecontents}{data_b.csv}
Thing;Weight
Dog 1;0
Dog 2;0
Cat 1;0
Cat 2;0
Cat 3;0
Parrot;0
\end{filecontents}

\begin{filecontents}{data_b_dog.csv}
Thing;Weight
Dog 1;50
Dog 2;45
\end{filecontents}

\begin{filecontents}{data_b_cat.csv}
Thing;Weight
Cat 1;10
Cat 2;10
Cat 3;11
\end{filecontents}

\begin{filecontents}{data_b_parrot.csv}
Thing;Weight
Parrot;3
\end{filecontents}

\begin{document}

\pgfplotstableread[col sep=semicolon]{data_b.csv}{\tableall}
\pgfplotstableread[col sep=semicolon]{data_b_dog.csv}{\tabledog}
\pgfplotstableread[col sep=semicolon]{data_b_cat.csv}{\tablecat}
\pgfplotstableread[col sep=semicolon]{data_b_parrot.csv}{\tableparrot}

\begin{tikzpicture}%
    \begin{axis}[%
        ybar=3mm,%
        xtick=data,%
        xticklabels from table={\tableall}{Thing},%
        x tick label style={rotate=60},%
        nodes near coords={%
            \pgfkeys{%
                /pgf/fpu=true,%
                /pgf/fpu/output format=fixed,%
            }%
            \pgfmathtruncatemacro{\Y}{\pgfplotspointmeta}%
            \ifthenelse{\Y=0}{}{\pgfmathprintnumber{\pgfmathresult}}%
        },%
        every axis plot/.append style={bar shift = 0}%
    ]%
        \addplot[draw=none] table [x expr=\coordindex,y index=1,col sep=semicolon] {\tableall};%
        \addplot[blue,fill] table [x expr=\coordindex,y index=1,col sep=semicolon] {\tabledog};%
        \addplot[green,fill] table [x expr=\coordindex+2,y index=1,col sep=semicolon] {\tablecat};%
        \addplot[red,fill] table [x expr=\coordindex+5,y index=1,col sep=semicolon] {\tableparrot};%
    \end{axis}
\end{tikzpicture}

\end{document}

In this MWE the numbers above the bars are wrong. I suppose that’s because I’m switching to integers. I’m not having that problem in my actual document. I have no clue where that comes from here. Anyway, that second MWE shows what I want to plot. This is the output:

Answer 1

Here is a way how you could achieve what you want. But be aware that this is not very efficient for large tables, because for each \addplot that uses the filter the whole table needs to be fully processed.

For details please have a look at the comments in the code.

% used PGFPlots v1.16
\begin{filecontents}{data.csv}
Thing;Weight
Dog 1;50
Dog 2;45
Cat 1;10
Cat 2;10
Cat 3;11
Parrot;3
\end{filecontents}
\documentclass[border=5pt]{standalone}
\usepackage{xstring}
\usepackage{pgfplots}
\usepackage{pgfplotstable}
    \pgfplotstableread[col sep=semicolon]{data.csv}{\table}
    \pgfplotsset{
        % filter away stuff in column #1 which starts with string #2 of
        % table \table
        discard if not/.style 2 args={
            % adapted from <https://tex.stackexchange.com/a/66716/95441>
            x filter/.code={
                \pgfplotstablegetelem{\coordindex}{#1}\of{\table}
                \IfBeginWith{\pgfplotsretval}{#2}{}{\def\pgfmathresult{}}
            },
        },
    }
\begin{document}
\begin{tikzpicture}
    \begin{axis}[
        ybar=3mm,
        bar shift=0pt,
        xtick=data,
        xticklabels from table={\table}{Thing},
        x tick label style={rotate=60},
    ]
        % dummy to plot all `xtick`s
        \addplot [forget plot] table [x expr=\coordindex,y expr=0] {\table};

        % cycle through entries
        \pgfplotsinvokeforeach {Dog,Cat,Parrot} {
            \addplot+ [
                nodes near coords,
                % apply style
                discard if not={Thing}{#1},
            ] table [x expr=\coordindex,y index=1] {\table};
        }
    \end{axis}
\end{tikzpicture}
\end{document}