# Combining Cohorts

    library(CohortConstructor)
    library(CohortCharacteristics)
    library(ggplot2)

For this example we’ll use the Eunomia synthetic data from the CDMConnector package.

    con <- DBI::dbConnect(duckdb::duckdb(), dbdir = eunomiaDir())
    cdm <- cdmFromCon(con, cdmSchema = "main",
                        writeSchema = c(prefix = "my_study_", schema = "main"))

Let’s start by creating two drug cohorts, one for users of diclofenac and another for users of acetaminophen.

    cdm$medications <- conceptCohort(cdm = cdm,
                                     conceptSet = list("diclofenac" = 1124300,
                                                       "acetaminophen" = 1127433),
                                     name = "medications")
    cohortCount(cdm$medications)

To check whether there is an overlap between records in both cohorts using the function `intersectCohorts()`.

    cdm$medintersect <- CohortConstructor::intersectCohorts(
      cohort = cdm$medications,
      name = "medintersect"
    )

    cohortCount(cdm$medintersect)

There are 6 individuals who had overlapping records in the diclofenac and acetaminophen cohorts.

We can choose the number of days between cohort entries using the `gap` argument.

    cdm$medintersect <- CohortConstructor::intersectCohorts(
      cohort = cdm$medications,
      gap = 365,
      name = "medintersect"
    )

    cohortCount(cdm$medintersect)

There are 94 individuals who had overlapping records (within 365 days) in the diclofenac and acetaminophen cohorts.

We can also combine different cohorts using the function `unionCohorts()`.

    cdm$medunion <- CohortConstructor::unionCohorts(
      cohort = cdm$medications,
      name = "medunion"
    )

    cohortCount(cdm$medunion)

We have now created a new cohort which includes individuals in either the diclofenac cohort or the acetaminophen cohort.

You can keep the original cohorts in the new table if you use the argument `keepOriginalCohorts = TRUE`.

    cdm$medunion <- CohortConstructor::unionCohorts(
      cohort = cdm$medications,
      name = "medunion",
      keepOriginalCohorts = TRUE
    )

    cohortCount(cdm$medunion)

You can also choose the number of days between two subsequent cohort entries to be merged using the `gap` argument.

    cdm$medunion <- CohortConstructor::unionCohorts(
      cohort = cdm$medications,
      name = "medunion",
      gap = 365,
      keepOriginalCohorts = TRUE
    )

    cohortCount(cdm$medunion)