9.4. Building a bar chart

A classic way of displaying categories with corresponding values is a bar chart. It consists of rectangular bars, and they are proportional to the represented values. The main purpose is to visually compare those values.

We can use vertical or horizontal bars.

How to do it…

We will use the pgfplots package. It’s for natively plotting in LaTeX with a convenient user interface. We will use it to produce a horizontal bar chart. Perform these steps:

  1. Start with a document class:

    \documentclass{article}
    
  2. Load the pgfplots package:

    \usepackage{pgfplots}
    \pgfplotsset{width=7cm,compat=1.8}
    
  3. Begin the document:

    \begin{document}
    
  4. Begin a TikZ picture, which will be the container for the plot:

    \begin{tikzpicture}
    
  5. Open an axis environment:

      \begin{axis}
    
  6. Give options to the axis:

     [
        title    = Contributions per category
                   at LaTeX-Community.org,
        xbar,
        y axis line style = { opacity = 0 },
        axis x line       = none,
        tickwidth         = 0pt,
        enlarge y limits  = 0.2,
        enlarge x limits  = 0.02,
        nodes near coords,
        symbolic y coords = {LaTeX, Tools,
                             Distributions, Editors},
      ]
    
  7. Add a plot:

      \addplot coordinates { (57727,LaTeX) (5672,Tools)
               (2193,Distributions) (11106,Editors) };
    
  8. Add another plot:

      \addplot coordinates { (14320,LaTeX) (1615,Tools)
               (560,Distributions)  (3075,Editors)  };
    
  9. Then add a legend:

      \legend{Topics, Posts}
    
  10. End the axis environment, the TikZ picture, and the whole document:

      \end{axis}
    \end{tikzpicture}
    \end{document}
    
  11. Compile, and take a look:

Bar plot

How it works…

The \addplot command does the plotting work; we called it with a set of specific coordinates. In our case, we used numeric values together with symbolic coordinates for the subjects.

We design the plot by options to the axis environment. This is the specific pgfplots environment with a lot of options for customizing. Here’s what we did:

  1. We provided a title.

  2. We set xbar as a style to get bars in the x direction. Specifically, this means that horizontal bars will be placed from y=0 to the x coordinate.

  3. Omitting unnecessary diagram parts means less distraction. This helps in focusing and understanding the contents. Therefore, we:

    • Chose a completely opaque line style for the y axis so that it won’t be printed
    • Hid the x axis using axis x line = none
    • Removed the x axis ticks by setting their width to 0
  4. Then we enlarged the x and y limits a bit to get a better display.

  5. We placed the nodes with values near the bars by enabling the nodes near coords option.

  6. We defined symbolic coordinates as y values so that we could assign numeric (x) values to (y) subjects.

To sum up, xbar defined the plot style, and symbolic y coords let us use string values. The other axis options were just for the design. There are many more possible settings, so for further customization, refer to the pgfplots manual. You can open it by entering texdoc pgfplots in command prompt or visiting http://texdoc.net/pkg/pgfplots.

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