Add preliminary RR to OR function

NAMESPACE

@@ -19,6 +19,7 @@ export(log_warnings)
 export(mill)
 export(read_timber)
 export(reorder_fields)
+export(risk_ratio_to_odds_ratio)
 export(save_csv)
 export(start_mill)
 export(sub_mill)

R/risk_ratio_to_odds_ratio.R

@@ -0,0 +1,61 @@
+
+
+#' @title
+#'   Calculate an odds ratio (OR) from a risk ratio (RR)
+#'
+#' @description
+#'   Calculate an odds ratio (OR) from a risk ratio (RR) and the outcome prevalence
+#'   in the unexposed (referent) group.
+#'
+#'
+#' @param .riskratio
+#'   numeric: risk ratio.
+#'
+#' @param .baseline
+#'   numeric: outcome prevalence in unexposed (referent) group.
+#'
+#' @return
+#'   An odds ratio.
+#'
+#' @export
+
+
+risk_ratio_to_odds_ratio <- function(.riskratio = NULL, .baseline = NULL) {
+
+  if ( !hasArg(.riskratio) | !is.numeric(.riskratio) ) {
+    cli::cli_abort(c(
+            "{.var .riskratio} must be a numeric vector.",
+      "x" = "You have supplied a {.cls {class(.riskratio)}} vector."
+    ))
+  }
+
+  if ( !hasArg(.baseline) | !is.numeric(.baseline) ) {
+    cli::cli_abort(c(
+            "{.var .baseline} must be a numeric vector.",
+      "x" = "You have supplied a {.cls {class(.baseline)}} vector."
+    ))
+  }
+
+  if ( .baseline < 0 | .baseline > 1) {
+    cli::cli_abort(c(
+            "{.var .baseline} must be probability between [0, 1].",
+      "x" = "You have supplied a value less than 0 or greater than 1."
+    ))
+  }
+
+  if ( .baseline == 0 | .baseline == 1 ) {
+    cli::cli_warn(c(
+      "{.var .baseline} should not be 0 or 1, with rare exception.",
+      "i" = "You have supplied a {.var .baseline} value of 0 or 1.",
+      "i" = "Run {.run help(risk_ratio_to_odds_ratio)} for more details."
+
+    ))
+  }
+
+  .oddsratio <- .riskratio * ( 1 - .baseline ) / ( 1 - .riskratio * .baseline)
+
+  return(.oddsratio)
+
+}
+
+