Fixes #225

techascent · Apr 7, 2021 · 0d663ca · 0d663ca
1 parent 37aa95c
commit 0d663ca
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Showing 3 changed files with 22 additions and 10 deletions.
diff --git a/src/tech/v3/dataset/base.clj b/src/tech/v3/dataset/base.clj
@@ -242,7 +242,7 @@
   index-seq - either keyword :all or list of indexes.  May contain duplicates.
   "
   [dataset colname-seq index-seq]
-  (when (dtype-proto/has-constant-time-min-max? index-seq)
+  (when (and index-seq (dtype-proto/has-constant-time-min-max? index-seq))
     (let [lmin (long (dtype-proto/constant-time-min index-seq))
           lmax (long (dtype-proto/constant-time-max index-seq))]
       (errors/when-not-errorf
@@ -253,10 +253,12 @@
   (let [index-seq (if (number? index-seq)
                     [index-seq]
                     index-seq)]
-    (when-not (or (nil? colname-seq)
-                  (and (sequential? colname-seq)
-                       (nil? (seq colname-seq))))
-      (ds-proto/select dataset colname-seq index-seq))))
+    (if-not (or (nil? colname-seq)
+                (and (sequential? colname-seq)
+                     (nil? (seq colname-seq)))
+                (nil? index-seq))
+      (ds-proto/select dataset colname-seq index-seq)
+      (ds-impl/empty-dataset))))
 
 (defn select-by-index
   "Trim dataset according to this sequence of indexes.  Returns a new dataset.

diff --git a/src/tech/v3/dataset/impl/dataset.clj b/src/tech/v3/dataset/impl/dataset.clj
@@ -21,7 +21,7 @@
 (set! *warn-on-reflection* true)
 
 
-(declare new-dataset map-entries)
+(declare new-dataset map-entries empty-dataset)
 
 ;;ported from clojure.lang.APersistentMap
 (defn- map-equiv [this o]
@@ -162,10 +162,7 @@
     (when-let [v (.valAt this k)]
       (clojure.lang.MapEntry. k v)))
   ;;No idea if this is correct behavior....
-  (empty [this] (new-dataset
-                 "_unnamed"
-                 {:name "_unnamed"}
-                 []))
+  (empty [this] (empty-dataset))
   ;;ported from clojure java impl.
   (cons [this e]
     (cond (instance? java.util.Map$Entry e)
@@ -450,3 +447,10 @@
 (defn dataset?
   [ds]
   (instance? Dataset ds))
+
+
+(defn empty-dataset
+  []
+  (new-dataset
+   "_unnamed"
+   nil))
diff --git a/test/tech/v3/dataset_test.clj b/test/tech/v3/dataset_test.clj
@@ -1044,6 +1044,12 @@
     (is (= 4 (ds/row-count data)))))
 
 
+(deftest empty-dataset-on-select-nothing
+  (let [dataset (ds/->dataset "test/data/stocks.csv")]
+    (is (= 0 (ds/row-count (ds/select-columns dataset nil))))
+    (is (= 0 (ds/row-count (ds/select-rows dataset nil))))))
+
+
 (comment
 
   (def test-ds (ds/->dataset