Make outliers work with empty input

src/metabase/feature_extraction/math.clj

@@ -148,7 +148,8 @@
    https://en.wikipedia.org/wiki/Interquartile_range"
   ([xs] (outliers identity xs))
   ([keyfn xs]
-   (let [{:keys [q1 q3 iqr]} (->> xs (transduce (map keyfn) h/histogram) h/iqr)
-         lower-bound         (- q1 (* 1.5 iqr))
-         upper-bound         (+ q3 (* 1.5 iqr))]
-     (remove (comp #(< lower-bound % upper-bound) keyfn) xs))))
+   (when (not-empty xs)
+     (let [{:keys [q1 q3 iqr]} (->> xs (transduce (map keyfn) h/histogram) h/iqr)
+           lower-bound         (- q1 (* 1.5 iqr))
+           upper-bound         (+ q3 (* 1.5 iqr))]
+       (remove (comp #(< lower-bound % upper-bound) keyfn) xs)))))

test/metabase/feature_extraction/math_test.clj

@@ -73,19 +73,22 @@
     :lag 1}
    {:autocorrelation -1.0
     :lag 1}
-   nil nil nil]
+   nil nil nil nil]
   [(autocorrelation (range 10))
    (autocorrelation [1 -1 1 -1 1 -1])
    (autocorrelation [1 2 3]) ; not significant
    (autocorrelation [1])
-   (autocorrelation [])])
+   (autocorrelation [])
+   (autocorrelation nil)])
 
 (expect
   [nil
-   #{50 100 35}]
+   #{50 100 35}
+   nil]
   (let [xs (vec (repeatedly 100 rand))]
     [(not-empty (outliers xs))
      (set (outliers (-> xs
                         (assoc-in [10] 50)
                         (assoc-in [30] 100)
-                        (assoc-in [70] 35))))]))
+                        (assoc-in [70] 35))))
+     (outliers nil)]))

test/metabase/feature_extraction/timeseries_test.clj

@@ -49,7 +49,9 @@
 
 (expect
   [[99]
+   []
    []]
   [(breaks 12 (map vector (range) (concat (repeat 100 10)
                                           (repeat 100 20))))
-   (breaks 12 (map vector (range) (take 100 (cycle (range 10)))))])
+   (breaks 12 (map vector (range) (take 100 (cycle (range 10)))))
+   (breaks 4 nil)])