Find recurrent dates in a small set (and get rid of non recurrent ones)
If it is a categorization problem then you should look for a classification algorithm, not a regression technique. The simplest classification algorithm is Logistic Regression. 

But by the looks of it, seems like you do not have a labelled data-set and if that's the case you should look for Clustering techniques. Clustering is a part of Unsupervised Learning Technique in ML which create clusters or groups of similar data points.