# Introduction to CodelistGenerator

## Creating a code list for dementia

For this example we are going to generate a candidate codelist for dementia, only looking for codes in the condition domain. Let’s first load some libraries

## Connect to the OMOP CDM vocabularies

CodelistGenerator works with a `cdm_reference` to the vocabularies tables of the OMOP CDM using the CDMConnector package.

    # example with postgres database connection details
    db <- DBI::dbConnect(RPostgres::Postgres(),
      dbname = Sys.getenv("server"),
      port = Sys.getenv("port"),
      host = Sys.getenv("host"),
      user = Sys.getenv("user"),
      password = Sys.getenv("password")
    )

    # create cdm reference
    cdm <- CDMConnector::cdm_from_con(
      con = db,
      cdm_schema = Sys.getenv("vocabulary_schema")
    )

## Check version of the vocabularies

It is important to note that the results from CodelistGenerator will be specific to a particular version of the OMOP CDM vocabularies. We can see the version of the vocabulary being used like so

    getVocabVersion(cdm = cdm)

    #> [1] "vocabVersion"

## A code list from “Dementia” (4182210) and its descendants

The simplest approach to identifying potential codes is to take a high-level code and include all its descendants.

    codesFromDescendants <- tbl(
      db,
      sql(paste0(
        "SELECT * FROM ",
        vocabularyDatabaseSchema,
        ".concept_ancestor"
      ))
    ) %>%
      filter(ancestor_concept_id == "4182210") %>%
      select("descendant_concept_id") %>%
      rename("concept_id" = "descendant_concept_id") %>%
      left_join(tbl(db, sql(paste0(
        "SELECT * FROM ",
        vocabularyDatabaseSchema,
        ".concept"
      )))) %>%
      select(
        "concept_id", "concept_name",
        "domain_id", "vocabulary_id"
      ) %>%
      collect()

    codesFromDescendants %>%
      glimpse()
    #> Rows: 151
    #> Columns: 4
    #> $ concept_id    <int> 35610098, 4043241, 4139421, 37116466, 4046089, 44782559,…
    #> $ concept_name  <chr> "Predominantly cortical dementia", "Familial Alzheimer's…
    #> $ domain_id     <chr> "Condition", "Condition", "Condition", "Condition", "Con…
    #> $ vocabulary_id <chr> "SNOMED", "SNOMED", "SNOMED", "SNOMED", "SNOMED", "SNOME…

This looks to pick up most relevant codes. But, this approach misses codes that are not a descendant of 4182210. For example, codes such as “Wandering due to dementia” (37312577; https://athena.ohdsi.org/search-terms/terms/37312577) and “Anxiety due to dementia” (37312031; https://athena.ohdsi.org/search-terms/terms/37312031) are not picked up.

## Generating a candidate code list using CodelistGenerator

To try and include all such terms that could be included we can use CodelistGenerator.

First, let’s do a simple search for a single keyword of “dementia”, including descendants of the identified codes.

    dementiaCodes1 <- getCandidateCodes(
      cdm = cdm,
      keywords = "dementia",
      domains = "Condition",
      includeDescendants = TRUE
    )

    dementiaCodes1%>%
      glimpse()
    #> Rows: 187
    #> Columns: 6
    #> $ concept_id       <int> 374326, 374888, 375791, 376085, 376094, 376095, 37694…
    #> $ found_from       <chr> "From initial search", "From initial search", "From i…
    #> $ concept_name     <chr> "Arteriosclerotic dementia with depression", "Dementi…
    #> $ domain_id        <chr> "Condition", "Condition", "Condition", "Condition", "…
    #> $ vocabulary_id    <chr> "SNOMED", "SNOMED", "SNOMED", "SNOMED", "SNOMED", "SN…
    #> $ standard_concept <chr> "standard", "standard", "standard", "standard", "stan…

## Comparing code lists

What is the difference between this code list and the one from 4182210 and its descendants?

    codeComparison <- compareCodelists(
      codesFromDescendants,
      dementiaCodes1
    )

    codeComparison %>%
      group_by(codelist) %>%
      tally()
    #> # A tibble: 2 × 2
    #>   codelist            n
    #>   <chr>           <int>
    #> 1 Both              151
    #> 2 Only codelist 2    36

What are these extra codes picked up by CodelistGenerator?

    codeComparison %>%
      filter(codelist == "Only codelist 2") %>%
      glimpse()
    #> Rows: 36
    #> Columns: 3
    #> $ concept_id   <int> 4041685, 4043378, 4044415, 4046091, 4092747, 4187091, 425…
    #> $ concept_name <chr> "Amyotrophic lateral sclerosis with dementia", "Frontotem…
    #> $ codelist     <chr> "Only codelist 2", "Only codelist 2", "Only codelist 2", …

## Review mappings from non-standard vocabularies

Perhaps we want to see what ICD10CM codes map to our candidate code list. We can get these by running

    icdMappings <- getMappings(
      cdm = cdm,
      candidateCodelist = dementiaCodes1,
      nonStandardVocabularies = "ICD10CM"
    )

    icdMappings %>%
      glimpse()
    #> Rows: 191
    #> Columns: 7
    #> $ standard_concept_id        <int> 372610, 374341, 374888, 374888, 374888, 374…
    #> $ standard_concept_name      <chr> "Postconcussion syndrome", "Huntington's ch…
    #> $ standard_vocabulary_id     <chr> "SNOMED", "SNOMED", "SNOMED", "SNOMED", "SN…
    #> $ non_standard_concept_id    <int> 45571706, 35207314, 1568088, 1568089, 37402…
    #> $ non_standard_concept_name  <chr> "Postconcussional syndrome", "Huntington's …
    #> $ non_standard_concept_code  <chr> "F07.81", "G10", "F02", "F02.8", "F02.811",…
    #> $ non_standard_vocabulary_id <chr> "ICD10CM", "ICD10CM", "ICD10CM", "ICD10CM",…

    readMappings <- getMappings(
      cdm = cdm,
      candidateCodelist = dementiaCodes1,
      nonStandardVocabularies = "Read"
    )

    readMappings %>%
      glimpse()
    #> Rows: 93
    #> Columns: 7
    #> $ standard_concept_id        <int> 372610, 372610, 372610, 372610, 372610, 372…
    #> $ standard_concept_name      <chr> "Postconcussion syndrome", "Postconcussion …
    #> $ standard_vocabulary_id     <chr> "SNOMED", "SNOMED", "SNOMED", "SNOMED", "SN…
    #> $ non_standard_concept_id    <int> 45446542, 45446553, 45453190, 45459905, 455…
    #> $ non_standard_concept_name  <chr> "Post-concussion syndrome", "[X]Post-trauma…
    #> $ non_standard_concept_code  <chr> "E2A2.00", "Eu06212", "E2A2.11", "E2A2.12",…
    #> $ non_standard_vocabulary_id <chr> "READ", "READ", "READ", "READ", "READ", "RE…