Histograms

In this section:

How to:

A histogram groups data values into classes and shows the frequency at which each class appears in the data set by displaying a series of columns whose width represents class intervals and whose areas are proportional to the corresponding frequencies. The shapes of histograms will vary depending on the choice of the size of the intervals. Histograms are designed for situations when the user is not interested in knowing the particular values, but in how those values are distributed across the data set.

The following image shows an example of a histogram.

Histogram example

WebFOCUS Visual Discovery enables you to see and understand locations and variations within the data by creating easy-to-read histograms with powerful features, such as:


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Procedure: How to Change the Orientation of a Histogram
  1. In the Visual Discovery Properties dialog box, click the Histogram tab.
  2. In the Style field, click the Horizontal button Horizontal Histogram button or the Vertical button Vertical Histogram button.
  3. Click Apply, and then click OK.

Tip: In the pop-up menu, if Horizontal has a check mark next to it then the graph has a horizontal orientation. Click Horizontal to remove the check mark and change the orientation to vertical.


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Procedure: How to Select the Histogram Scale
  1. In the Visual Discovery Properties dialog box, click the Histogram tab.
  2. In the x-axis scale field, select:
    • Linear as the default presentation.
    • Root, which is a factor of a number that, when multiplied by itself, gives the number. For example, the square root of 9 is 3. This is useful when looking at highly skewed distributions because it evenly reduces the positions of the items, making them appear closer together.
    • Log, which is the exponent that indicates the power to which a number is raised to produce a given number. For example, the logarithm of 100 to the base 10 is 2. When you have a large range of an item (like one item in a million), log is useful because it maintains the relative position of the item while reducing the extremes.
  3. Click OK and then click Apply.

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Smoothing a Histogram

How to:

Reference:

Smoothing is a statistical technique in which data is averaged to remove extreme highs and lows. If little smoothing is applied, the data distribution reflects the exact data sample. Higher degrees of smoothing reduce the extreme highs and lows in the sample to show the idealized distribution of data.



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Procedure: How to Smooth a Histogram
  1. In the Visual Discovery Properties dialog box, click the Histogram tab.
  2. In the Smoothing section, move the slider bar to the right or left to increase or decrease the amount of smoothing. The change in smoothing appears immediately.


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Reference: Histogram Tab

The following image shows the Histogram tab in the Visual Discovery Properties dialog box.

Histogram Tab

Style

Orientation is horizontal or vertical. See How to Change the Orientation of a Histogram.

X Axis Scale

Is linear, root, or log. See How to Select the Histogram Scale.

Stack Colors

A glyph may be colored to show two fields that have been colored by a third field. The colors are stacked on a glyph. See Assigning Color to the Data and the Graph.

Smoothing

A statistical technique in which data is averaged to remove extreme highs and lows. See Smoothing a Histogram.



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Reference: Histogram Pop-up Menu

The pop-up menu appears when you right-click a Visual Discovery control in the analytical dashboard. These options do not appear when you are developing in HTML Composer.

Horizontal

Is the orientation of the graph. If Horizontal is checked, the orientation of the graph is horizontal. If it is not checked, the orientation is vertical.

Stack Colors

A glyph may be colored to show two fields that have been colored by a third field. The colors are stacked on a glyph. See Assigning Color to the Data and the Graph.

Scale

Changes the scale of the histogram to Linear, Root, or Log.

Undo

Reverses the previous action. You may repeatedly undo actions retained in the history file for your current session by selecting Undo over and over again. A description of the previous action appears on the pop-up menu. If you have performed no action, Undo is not available for selection and no action appears to the right of the word Undo.

Redo

Restores the previous undo action. If you have performed no action, Redo is not available for selection and no action appears to the right of the word Redo.

Select All

Selects all of the items in the graph. When you choose Select All, any previous selections are ignored. Selection state returns to the original setting.

Unselect All

When selected, all of the items become unselected. All items appear in the unselected color (gray, by default) or are hidden in the graph (if hide unselected is active).

Toggle All

Reverses the selection state of items. Selected items become unselected and unselected items become selected.

Exclude Unselected

Excludes (temporarily removes) items from the graph.

Restore Excluded

Restores the items you excluded. If you accidentally excluded the unselected, this menu option restores those excluded items.

Save Image

Enables you to save the graph to a GIF or JPEG file.

Copy Image

Enables you to copy the selected component and paste it to another file.

Properties

Takes you to the collection of tabs available for the respective visualization component. Common tabs include Data, Selecting, and Colors.


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