K-Means Cluster Analysis Efficiency
The k-means cluster analysis command is efficient primarily because it does not compute the distances between all pairs of cases, as do many clustering algorithms, including the algorithm that is used by the hierarchical clustering command.
For maximum efficiency, take a sample of cases and select the Iterate and classify method to determine cluster centers. Select Write final as. Then restore the entire data file and select Classify only as the method and select Read initial from to classify the entire file using the centers that are estimated from the sample. You can write to and read from a file or a dataset. Datasets are available for subsequent use in the same session but are not saved as files unless explicitly saved prior to the end of the session. Dataset names must conform to variable-naming rules. See the topic Variable names for more information.