1 files changed, 95 insertions, 0 deletions
diff --git a/jstests/core/query/mr/mr_compute_avg.js b/jstests/core/query/mr/mr_compute_avg.js
new file mode 100644
index 00000000000..b5934b310d7
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+++ b/jstests/core/query/mr/mr_compute_avg.js
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+// Tests a mapReduce for a relatively simple use case of computing an average. This is interesting
+// because it does more than a simple sum for the reduce function and also needs to use a finalize
+// function to do the final division to compute the average from the sum and totals.
+//
+// Cannot implicitly shard accessed collections because mapReduce cannot replace a sharded
+// collection as output.
+// The test runs commands that are not allowed with security token: mapReduce.
+// @tags: [
+//   not_allowed_with_security_token,
+//   assumes_unsharded_collection,
+//   # mapReduce does not support afterClusterTime.
+//   does_not_support_causal_consistency,
+//   does_not_support_stepdowns,
+//   uses_map_reduce_with_temp_collections,
+// ]
+(function() {
+"use strict";
+
+const coll = db.mr_blog_posts;
+coll.drop();
+
+assert.commandWorked(coll.insert([
+    {
+        _id: "blog 1",
+        author: "x",
+        comments: [{user_id: "a", txt: "asdasdasd"}, {user_id: "b", txt: "asdasdasdasdasdasdas"}]
+    },
+    {
+        _id: "blog 2",
+        author: "y",
+        comments: [{user_id: "b", txt: "asdasdasdaaa"}, {user_id: "c", txt: "asdasdasdaasdasdas"}]
+    }
+]));
+
+function mapFn() {
+    for (let comment of this.comments) {
+        emit(comment.user_id, {totalSize: comment.txt.length, num: 1});
+    }
+}
+
+function reduceFn(user_id, values) {
+    let reduced = {totalSize: 0, num: 0};
+    for (let value of values) {
+        reduced.totalSize += value.totalSize;
+        reduced.num += value.num;
+    }
+    return reduced;
+}
+
+const outputColl = db.mr_compute_avg_out;
+outputColl.drop();
+
+function reformat(cmdResult) {
+    let x = {};
+    let cursor;
+    if (cmdResult.results)
+        cursor = cmdResult.results;
+    else
+        cursor = outputColl.find();
+    cursor.forEach(result => {
+        x[result._id] = result.value;
+    });
+    return x;
+}
+
+function finalizeFn(user_id, res) {
+    res.avg = res.totalSize / res.num;
+    return res;
+}
+
+let res = coll.mapReduce(mapFn, reduceFn, {finalize: finalizeFn, out: outputColl.getName()});
+assert.commandWorked(res);
+let resultAsSingleObj = reformat(res);
+assert.eq(9, resultAsSingleObj.a.avg, () => tojson(resultAsSingleObj));
+assert.eq(16, resultAsSingleObj.b.avg, () => tojson(resultAsSingleObj));
+assert.eq(18, resultAsSingleObj.c.avg, () => tojson(resultAsSingleObj));
+outputColl.drop();
+
+res = coll.mapReduce(mapFn, reduceFn, {finalize: finalizeFn, out: {inline: 1}});
+assert.commandWorked(res);
+resultAsSingleObj = reformat(res);
+assert.eq(9, resultAsSingleObj.a.avg, () => tojson(resultAsSingleObj));
+assert.eq(16, resultAsSingleObj.b.avg, () => tojson(resultAsSingleObj));
+assert.eq(18, resultAsSingleObj.c.avg, () => tojson(resultAsSingleObj));
+outputColl.drop();
+assert(!("result" in res), () => `Expected inline output with 'results': ${tojson(res)}`);
+
+res = coll.mapReduce(mapFn, reduceFn, {finalize: finalizeFn, out: {inline: 1}});
+assert.commandWorked(res);
+resultAsSingleObj = reformat(res);
+assert.eq(9, resultAsSingleObj.a.avg, () => tojson(resultAsSingleObj));
+assert.eq(16, resultAsSingleObj.b.avg, () => tojson(resultAsSingleObj));
+assert.eq(18, resultAsSingleObj.c.avg, () => tojson(resultAsSingleObj));
+assert(!("result" in res), () => `Expected inline output with 'results': ${tojson(res)}`);
+}());