Can I use ELKI to just do PCA on my input dataset and get the transformed set as text file? The output format of the file does not really matter.
I see PCA is not available as an algorithm but only as a dbc.filter. I tried invoking the NullAlgorithm after the PCA filter and then the ResultWriter but it does not output the data set (which is not surprising since it returns null as a Result).
Maybe an algorithm that passes through the results from the filter would be a convenient functionality? Since I'm not yet comfortable at all with the code, maybe somebody could point me to the steps I need to take to implement something like that.
You can indeed use the algorithm
-algorithm clustering.trivial.TrivialAllInOne
to cause the default result writer to dump your data. The NullAlgorithm does not work, because the result writer then is not sure what to write. If it sees a clustering result with a single cluster named cluster, it will write it to a file cluster.txt.
I occasionally use this to project data, too. On the long run, I would love to see ELKI be extended with a nice preprocessing interface.