Where can I find a software library for pairwise matching (ideally, Python, R, Java)? I am looking for a library that implements a pairwise ranking algorithm. For example, if I have 200 writing samples from 100 people (two samples from each individual) and I want to identify which samples belong together (i.e., were written by the same person), what library could I use?
If you can transform those sentences into number vectors (e.g. into a bag of words or tf-idf representation), I guess you could use k-Means or hierarchical clustering functionality from Orange, a GUI and machine learning library written in Python.

It also has an add-on for text mining specifically, but I cannot attest to it as I haven't tried it yet.