<histogram>

An histogram object represents a set of tabulated frequencies. It shows what proportion of cases fall into specific bins or categories.

Example

   <histogram id="example">
    <about>
      <label>Single dataset</label>
      <description>This is an example of a single histogram.</description>
    </about>
    <xaxis>
      <label>Time</label>
      <description>Time during the experiment.</description>
      <units>s</units>
      <marker>
        <at>5</at>
        <label>Look here</label>
        <style>-foreground red -linewidth 2</style>
       </marker>
    </xaxis>
    <yaxis>
      <label>Voltage v(11)</label>
      <description>Output from the amplifier.</description>
      <units>V</units>
    </yaxis>
    <component>
      <xy>
       1 0.99
       2 0.34
       4 0.57 
       6 0.22
       7 0.11
       </xy>
     </component>
   </histogram>

How to describe the data

Each <component> element describes the values of the histogram. There following sub-elements that can be used to describe the data.

<xy>

The data is in name/value pairs. The name is a string that will label the bar. The value is the frequency. The order of the bars is the order of the pairs.

   <histogram id="namevalues">
    ...
    <component>
      <xy>
        First 0.99
        Second 0.34
        Third 0.57 
        Fourth 0.22
        "Another value" 0.11
      </xy>
     </component>
   </histogram>

<xhw>

This is exactly like the <xy> element except that it includes a third value per line that is the width of the bar. The should be used when you want non-uniform bars.

   <histogram id="xhw">
    ...
    <component>
      <xhw>
       1 0.99 1
       2 0.34 1
       4 0.57 2
       6 0.22 1
       7 0.11 1
      </xhw>
     </component>
   </histogram>

The x-value is a string that will label the bar. The y-value is a number representing the frequency. The last value is the width of the bar in graph coordinates.

<xvector> and <yvector>

These two elements can be used if you want to represent the data as separate vectors. The x-vector values are the strings representing the labels of the bars. The y-vector values are numbers representing the frequencies. The widths of the bars are uniform.

  <histogram id="vectors">
   ...
   <component>
     <xvector>1 2 4 6 7</xvector>
     <yvector>0.99 0.34 0.57 0.22 0.11<yvector>
   </component>
  </histogram>

Tags

When a histogram is produced as an output result, the following tags are significant:

<about><label>

identifies the result in the combobox when selecting various results.

<about><description>

is displayed in a tooltip when you mouse over the selector, giving a more detailed explanation of what this result represents.

<xaxis><description>

is displayed in a tooltip when you mouse over the x-axis. It gives more information about the physical quantities being plotted.

<yaxis><description>

is displayed in a tooltip when you mouse over the y-axis. It gives more information about the physical quantities being plotted.

Note that the <xaxis> sections can have one or more <marker> objects. Each marks an axis value with an optional label.

<xaxis><marker><at>

is the location along the x-axis of a vertical line.

<xaxis><marker><label>

is the text displayed at the top/right of the vertical line.

<xaxis><marker><style>

is a list of style attributes for the vertical line.

<yaxis><marker><at>

is the location along the y-axis of a horizontal line.

<yaxis><marker><label>

is the text displayed at the above of the horizontal line.

<yaxis><marker><style>

is a list of style attributes for the horizontal line.

[Need description of available style attributes.]