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1 files changed, 17 insertions, 0 deletions

diff --git a/util/count.js b/util/count.js
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+++ b/util/count.js
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+module.exports = function count(arr) {
+  // Counts the number of times the items of an array appear (only on the top
+  // level; it doesn't search through nested arrays!). Returns a map of
+  // item -> count.
+
+  const map = new Map()
+
+  for (let item of arr) {
+    if (map.has(item)) {
+      map.set(item, map.get(item) + 1)
+    } else {
+      map.set(item, 1)
+    }
+  }
+
+  return map
+}