Dendrograms
A dendrogram is the graphical representation of a statistical tool called “hierarchical agglomerative clustering”. Hierarchical clustering aims at defining a sequence of N clusterings of k clusters, for k Î [1,...,N], so that the resulting clusters form a nested sequence.
The agglomerative algorithm starts with the initial set of N attributes, considered as N singleton clusters. At each step it proceeds by identifying the two most similar clusters and merging them to form a new cluster. This step is repeated until all attributes have been merged together into a single cluster.
The similarity among the attributes is measured by means of the correlation coefficient which takes its values into the range [-1,1]:
| rho(x,y) = cov(x,y) / σx.σy |
where, cov(x,y) represents the covariance between variables X and Y; and σx is the standard-deviation of variable X.
Create a Dendrogram
To launch the dendrogram editor, select Explore > Dendrogram from the menu. Alternatively, click the icon (
) in the sidebar and then click Add new. The parameters for a dendrogram are defined on two tabs at the top of the page: Data and Properties.
On the Data tab:
- Select a Data source from the list.
Select an Object set from the list.
- Select an attribute from the Attribute list, and click Input.
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Attributes are listed alphabetically. To find an attribute, use the scroll bar or enter the name in the search field |
On the Properties tab:
- Enter a chart Title and select the check box if you want it to show.
- Click Compute to load the data and display two tabs: Dendrogram and Correlation Matrix.
Control the View
To change the view, use the control menu below the dendrogram to modify the zoom. To modify the data, click Edit and revise the parameters.
To export the chart:
- Click More actions and select a file format; either PNG or SVG.
- Enter a file name and path, and click Export.
Example Visualization
The following example illustrates the weekly average of electrical consumption.