Can't replicate this graph using TikZ

Question

I'm having trouble replicating this graph

I know it's silly to do a graph with so little info, but my teacher demands it.. go figure...

I can't seem to make the bars stick together. It's my first attempt at TikZ ever...

what I've done so far:

\documentclass{article}  
\usepackage{pfgplots}
\begin{document}  
    \begin{tikzpicture}     
     \begin{axis}[ symbolic x coords={18S, HNF1, Normalização dos valores para 18S}, xtick=data]  
    \addplot[ybar,fill=black] coordinates { 
      (18S,42) 
      (HNF1,50) 
      (Normalização dos valores para 18S,80) 
 }; 
    \addplot[ybar,fill=gray] coordinates { 
      (18S,50) 
      (HNF1,30) 
      (Normalização dos valores para 18S, 100) 
 };  
  \end{axis}   
\end{tikzpicture}  
\end{document}

Answer 1

There are a number of issues with the code you posted:

• By specifying ybar in each \addplot command, you cause the bars to be put on top of each other. Specify the ybar once in the \axis command.
• the ybar (or xbar) allows a value which determines the separation between bars at the same x (or y) tick. Set this to 0 to get the bars adjacent.
• Symbolic axes don't like accented characters as far as I can tell. So the way around this problem (which also makes entering the data easier), is to use an arbitrary symbolic label like {A,B,C} and then use xticklabels to supply the labels. This also allows you to put the long label into a tabular environment, so it will wrap correctly.)
• To get the long label to fit you need to enlarge the limits.

Here's a new version of your plot: (by the way, your numbers don't match your picture!)

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage{pgfplots,amsmath,calc}
\usetikzlibrary{patterns}
\pgfplotsset{width=7cm,compat=1.3}

\begin{document}


\begin{tikzpicture}     
  \begin{axis}[ybar=0pt,
    symbolic x coords={A, B, C}, 
    xtick={A, B, C}, 
    xticklabels={18S, HNF1,
       \begin{tabular}{c}Normalização\\dos valores\\para 18S\end{tabular}},
    enlargelimits=0.3,bar width=20pt]  
    \addplot[fill=black] coordinates { 
      (A,42) 
      (B,50) 
      (C,80) 
 }; 
    \addplot[fill=gray] coordinates { 
      (A,50) 
      (B,30) 
      (C, 100) 
 };  
  \end{axis}   
\end{tikzpicture} 



\end{document}