Sketch join_by() implementation

R/utils-join_by.R

@@ -0,0 +1,59 @@
+# Testing
+# join_spec <- join_by(x, y >= z)
+# prep_join_by(join_spec)
+
+# TODO (working list)
+#  * Move join_by to separate file
+#  * Renaming columns pre-join?
+#  * Review dplyr semantics with keep = FALSE & keep = TRUE
+#  * What to do with between/overlaps/etc.
+
+# Need to export/create separate file
+join_by <- function(...) {
+  dots <- enquos(...)
+  dots <- map(dots, quo_squash)
+
+  set_class(dots, c("tidytable_join_by", "list"))
+}
+
+is_join_by <- function(x) {
+  inherits(x, "tidytable_join_by")
+}
+
+prep_join_by <- function(x, type = "left") {
+  if (type == "left") {
+    x <- flip_inputs(x)
+  }
+  on <- call2(".", !!!x)
+  on
+}
+
+flip_inputs <- function(x) {
+  map(x, flip_input)
+}
+
+flip_input <- function(x) {
+  if (is_call(x, c("==", "<=", ">=", ">", "<"))) {
+    out <- flip_operator(x)
+    out[[3]] <- x[[2]]
+    out[[2]] <- x[[3]]
+    out
+  } else {
+    out <- x
+  }
+  out
+}
+
+flip_operator <- function(x) {
+  old_operator <- as.character(x[[1]])
+  new_operator <- case_match(
+    old_operator,
+    "<=" ~ ">=",
+    ">=" ~ "<=",
+    ">" ~ "<",
+    "<" ~ ">",
+    .default = old_operator
+  )
+  x[[1]] <- sym(new_operator)
+  x
+}