Criando um gráfico de barras com um eixo x ordinal?

Question

Estou tentando criar um gráfico de barras onde os valores ao longo do eixo x não são relevantes. Meu código atual é este:

\documentclass{article}
\beging{document}
\begin{figure}
\centering
     \begin{tikzpicture}
        \begin{axis}[ylabel=Similarity,
                    ybar]
            \addplot table[y=Pref, col sep=comma] {5_Results/evalresults.csv};
            \addplot table[y=Rec, col sep=comma] {5_Results/evalresults.csv};

        \end{axis}
    \end{tikzpicture}
    \caption{A bar chart of user and course similarity}
    \label{evalresultsbar}
\end{figure}
\end{document}

No entanto, isso gera este gráfico. Não estou apenas procurando remover os valores ao longo do eixo x, também quero impedir que as barras sejam empilhadas umas sobre as outras.

Minha saída desejada seria semelhante a este gráfico gerado pelas planilhas do Google:

O conteúdo de evalresults.csv

Pref,Rec,label
0.00,14.29,a
0.00,16.67,a
0.00,16.67,a
0.00,20.00,a
0.00,20.00,a
0.00,25.00,a
0.00,33.33,a
0.00,33.33,a
0.00,33.33,a
0.00,50.00,a
0.00,50.00,a
0.00,50.00,a
0.00,50.00,a
0.00,50.00,a
0.00,60.00,a
0.00,60.00,a
0.00,60.00,a
33.33,25.00,a
33.33,25.00,a
33.33,33.33,a
33.33,33.33,a
33.33,60.00,a
33.33,60.00,a
33.33,66.67,a
33.33,75.00,a
33.33,75.00,a
33.33,75.00,a
33.33,80.00,a
33.33,80.00,a
33.33,100.00,a
66.67,75.00,a
66.67,80.00,a
66.67,100.00,a
66.67,100.00,a
66.67,100.00,a
66.67,100.00,a
100.00,100.00,a

Answer 1

Você precisará especificar a coordenada x de alguma forma, então adicione x expr=\coordindexas opções para table, como visto abaixo.

Eu adicionei alguns comentários no código

\documentclass[border=5mm]{standalone}
\usepackage{pgfplots}
\pgfplotsset{compat=1.14}
\usepackage{pgfplotstable} % for pgfplotstableread, but you can use the filename in the \addplot as you did instead
\pgfplotstableread[col sep=comma]{
Pref,Rec,label
0.00,14.29,a
0.00,16.67,a
0.00,16.67,a
0.00,20.00,a
0.00,20.00,a
0.00,25.00,a
0.00,33.33,a
0.00,33.33,a
0.00,33.33,a
0.00,50.00,a
0.00,50.00,a
0.00,50.00,a
0.00,50.00,a
0.00,50.00,a
0.00,60.00,a
0.00,60.00,a
0.00,60.00,a
33.33,25.00,a
33.33,25.00,a
33.33,33.33,a
33.33,33.33,a
33.33,60.00,a
33.33,60.00,a
33.33,66.67,a
33.33,75.00,a
33.33,75.00,a
33.33,75.00,a
33.33,80.00,a
33.33,80.00,a
33.33,100.00,a
66.67,75.00,a
66.67,80.00,a
66.67,100.00,a
66.67,100.00,a
66.67,100.00,a
66.67,100.00,a
100.00,100.00,a
}\data
\begin{document}    
\begin{tikzpicture}
\begin{axis}[
  ylabel=Similarity,
  ybar,
  % reduce bar width
  bar width=1pt,
  % to remove whitespace below bars
  ymin=0,
  % only want the x-axis on the bottom
  axis x line=bottom,
  % add some horizontal space between bars and axis limits
  enlarge x limits=0.05,
  % don't draw the ticks
  tick style={draw=none},
  % remove x ticks
  xtick=\empty,
  % enable grid
  grid=major,
  % don't draw the vertical lines for the y-axes
  every outer y axis line/.style={draw=none},
  %position legend outside the axis, top right
  legend pos=outer north east,
  % don't draw box around legend
  legend style={draw=none}
]
    \addplot [fill=red!50,draw=none] table[x expr=\coordindex,y=Pref, col sep=comma] {\data};
    \addplot [fill=blue!30,draw=none] table[x expr=\coordindex,y=Rec, col sep=comma] {\data};

   \addlegendentry{Pref}
   \addlegendentry{Rec}

\end{axis}
\end{tikzpicture}
\end{document}