retention2: Alternative (and possibly faster) retention calculation.
In jbryer/retention: Retention and Completion for Higher Education

Alternative (and possibly faster) retention calculation.

retention2(students, graduates, months = c(15, 24, 36, 48, 72, 96),
  warehouseDateColumn = "CREATED_DATE", gradColumn = "START_DATE",
  studentIdColumn = "CONTACT_ID_SEQ", degreeColumn = "DEGREE_CODE",
  persistColumn = "Persist")

`students`	a data frame of enrolled students. This data frame should be structured like a warehouse data where a student is represented for each cohort (i.e. warehouseDateColumn) in which they are enrolled.
`warehouseDateColumn`	the name of the column corresponding to the warehouse date, or cohort. Each unique date will thereby define a cohort.
`gradColumn`	the name of the column in the `graduates` data frame corresponding to the graduation date.
`studentIdColumn`	the name of the column corresponding the student's id.
`degreeColumn`	(optional) the name of the column corresponding to the degree the student is enrolled in (within students) or graduated (within graduates). If omitted, then `Transferred` and `Graduated Other` levels in the returned `Status` variable will have no values set.
`persistColumn`	(optional) the name of the column correspondinng to whether the student is persisting within that month or not. If omitted, the `Persisting` column will not be present in the returned data frame. The column must be `logical`.
`graduates`	a data frame of graduates, or degrees earned.