build_cohort: Converts a longitudinal data set from e.g. 'prev_terms' to a...
In rOpenHealth/rEHR: Manipulating and Analysing Electronic Health Record Data

Converts a longitudinal data set from e.g. prev_terms to a cohort dataset. The dataset has a single row for each patient and includes only patients in the numerator or denominator for whichever cohort type is chosen. Columns are added for start and end dates and for start and end times as integer differences from the cohort start date. A binary column is added for membership of the case group. All patients with start date > end date are removed from the dataset.

1 2	build_cohort(dat, cohort_type = c("incid", "prev"), cohort_start, cohort_end, diagnosis_start = "eventdate")

`dat`	dataframe as output from a call to `prev_terms`
`cohort_type`	character either 'incid' or 'prev'. This selects the numerators and denominators for that type of cohort
`cohort_start`	ISO date character string for the start of the cohort
`cohort_end`	ISO date character string for the end of the cohort
`diagnosis_start`	character string for the name of the diagnosis variable used to define the start dates, or NULL if the diagnosis date is not to be included in the definition of start dates.