1 files changed, 35 insertions, 0 deletions
diff --git a/ui/lib/iterator.js b/ui/lib/iterator.js
new file mode 100644
index 0000000..1d6a740
--- /dev/null
+++ b/ui/lib/iterator.js
@@ -0,0 +1,35 @@
+export function* map(xs, fn) {
+  for (const x of xs) {
+    yield fn(x);
+  }
+}
+
+export function reduce(xs, fn, initial) {
+  let value = initial;
+  for (const x of xs) {
+    value = fn(value, x);
+  }
+  return value;
+}
+
+export function* chunkBy(xs, keyFn, coalesceFn) {
+  let chunk;
+  let key;
+  for (const x of xs) {
+    const newKey = keyFn(x);
+
+    if (key === undefined) {
+      chunk = [x];
+    } else if (coalesceFn(key, newKey)) {
+      chunk.push(x);
+    } else {
+      yield { key, chunk };
+
+      chunk = [x];
+    }
+    key = newKey;
+  }
+  if (chunk !== undefined) {
+    yield { key, chunk };
+  }
+}