From a54e4d1834a06f82164acbbe64dbbdc97e98170b Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=EA=B9=80=EC=84=B1=EB=B0=B1?= <dumbuk12@naver.com>
Date: Tue, 6 Aug 2024 20:34:22 +0900
Subject: [PATCH] Itertools/pairwise (#40)

* feat(pairwise): implement operation

* chore: apply changeset
---
 .changeset/tough-bananas-end.md               |  5 ++++
 .../python/src/itertools/pairwise.test.ts     | 26 +++++++++++++++++++
 packages/python/src/itertools/pairwise.ts     | 19 ++++++++++++++
 3 files changed, 50 insertions(+)
 create mode 100644 .changeset/tough-bananas-end.md
 create mode 100644 packages/python/src/itertools/pairwise.test.ts
 create mode 100644 packages/python/src/itertools/pairwise.ts

diff --git a/.changeset/tough-bananas-end.md b/.changeset/tough-bananas-end.md
new file mode 100644
index 0000000..20c77e9
--- /dev/null
+++ b/.changeset/tough-bananas-end.md
@@ -0,0 +1,5 @@
+---
+"@iter-x/python": patch
+---
+
+implement pairwise operation
diff --git a/packages/python/src/itertools/pairwise.test.ts b/packages/python/src/itertools/pairwise.test.ts
new file mode 100644
index 0000000..285b693
--- /dev/null
+++ b/packages/python/src/itertools/pairwise.test.ts
@@ -0,0 +1,26 @@
+import { describe, expect, it } from "vitest";
+import { pairwise } from "./pairwise";
+
+describe("pairwise", () => {
+  it("should generate pairwise iterator", () => {
+    const result = [...pairwise("ABCDEFG")];
+    expect(result).toEqual([
+      ["A", "B"],
+      ["B", "C"],
+      ["C", "D"],
+      ["D", "E"],
+      ["E", "F"],
+      ["F", "G"],
+    ]);
+  });
+
+  it("should not generate any values when iterator is empty", () => {
+    const result = [...pairwise("")];
+    expect(result).toEqual([]);
+  });
+
+  it("should not generate any values when iterator is short to be pair", () => {
+    const result = [...pairwise("A")];
+    expect(result).toEqual([]);
+  });
+});
diff --git a/packages/python/src/itertools/pairwise.ts b/packages/python/src/itertools/pairwise.ts
new file mode 100644
index 0000000..3254c4e
--- /dev/null
+++ b/packages/python/src/itertools/pairwise.ts
@@ -0,0 +1,19 @@
+import { iter } from "../built-in";
+
+/**
+ * @example pairwise('ABCDEFG') -> AB BC CD DE EF FG
+ */
+export function* pairwise<T>(iterable: Iterable<T>): IterableIterator<[T, T]> {
+  const it = iter(iterable);
+  let item = it.next();
+  let prevValue = item.value;
+
+  if (item.done) return;
+
+  while (true) {
+    item = it.next();
+    if (item.done) return;
+    yield [prevValue, item.value];
+    prevValue = item.value;
+  }
+}