title: Using Spark to correlate non-numeric data
body: <p>I am trying to use Spark/MLlib to obtain the correlation coefficient between multiple columns in a set of data. I am having no problem with the numeric columns, where I have been successfully able to calculate the Pearson correlation. However, I cannot figure out how to correlate string and other non-numeric data. The documentation notes that the Spearman correlation is generally used for this purpose, but all of the examples I have seen seem to use numeric data, even in the Spearman case.</p>