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  <title>Lodash _.meanBy — traps</title>
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  <h1>_.meanBy — missing fields, null, string values</h1>
  <pre id="out"></pre>
  <script src="https://cdn.jsdelivr.net/npm/lodash@4.17.21/lodash.min.js"></script>
  <script>
    (function () {
      var rows = [{ n: 1 }, { x: 2 }, { n: 3 }];
      var usable = rows.filter(function (r) { return r.n != null; });
      var withNull = [{ n: 1 }, { n: null }, { n: 3 }];
      var mixed = [{ n: 1 }, { n: "20" }, { n: 3 }];
      var lines = [
        'meanBy(rows, "n")          => ' + _.meanBy(rows, "n"),
        '(filtered) meanBy(usable, "n") => ' + _.meanBy(usable, "n"),
        'meanBy(withNull, "n")      => ' + _.meanBy(withNull, "n"),
        'meanBy(mixed, "n")         => ' + _.meanBy(mixed, "n")
      ];
      document.getElementById("out").textContent = lines.join("\n");
    })();
  </script>
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Lodash _.meanBy — missing-field trap (Try It)