在 Clojure 中从特定于类型的数组创建通用数组

Question

I am working with JFreeChart in clojure and came across a situation I'd like help.

JFreeChart's DefaultXYDataset has a method addSeries which is used to add series to the chart. The data is supposed to be an array containing two arrays which are type specific(Array of doubles). I therefore wrote the following code thinking it would work but i get a ClassCastException that class [Ljava.lang.Object; cannot be cast to class [[D ([Ljava.lang.Object; and [[D are in module java.base of loader 'bootstrap') class [Ljava.lang.Object; cannot be cast to class [[D ([Ljava.lang.Object; and [[D are in module java.base of loader 'bootstrap') .

(doto _dataset
  (.addSeries "S1" (to-array (conj
                               []
                               (double-array (range 10))
                               (double-array (range 10))))))

After looking through i realized that to-array converts the two nested arrays to #object["[Ljava.lang.Object;" 0x491223e7 "[Ljava.lang.Object;@491223e7"] #object["[Ljava.lang.Object;" 0x491223e7 "[Ljava.lang.Object;@491223e7"] instead of the intended #object["[D" 0x4f5cf37 "[D@4f5cf37"] #object["[D" 0x6d895193 "[D@6d895193"] . Is there a way of combining them to a generic array without converting them to arrays of longs? Maybe another method apart from to-array . Any other suggestions are welcome. Thanks.

Edit: @bfabry answer will work, i could use make-array and then use aset-double but this will result in me looping through the two sequences and assign their values to the main array. I am trying to avoid this as the two datasets can be quite big, even up to 300k items each.

Answer 1

That's two dimensional array, not an array of two array objects. You'll need to use make-array and aset-double to make the array you want.

user=> (class (make-array Double/TYPE 2 2))
[[D

https://clojuredocs.org/clojure.core/make-array