[column-parsers] Add an option to disable na/NA as missing

 - Not 100% sure this is a great idea or the best implementation
 - c.f., this slack thread: https://clojurians.slack.com/archives/C0BQDEJ8M/p1708666522549399
 - Not sure about the option name, feel free to change
 - Slightly sketched by this similar-looking macro: https://github.com/techascent/tech.ml.dataset/blob/7b819dd81ccd58812ed189009cede6fe3ec7204b/src/tech/v3/dataset/impl/column_data_process.clj#L19-L26

src/tech/v3/dataset/io/column_parsers.clj

@@ -172,7 +172,7 @@
 
 (defn- missing-value?
   "Is this a missing value coming from a CSV file"
-  [value]
+  [value options]
   ;;fastpath for numbers
   (cond
     (or (instance? Double value) (instance? Float value))
@@ -181,7 +181,8 @@
     (or (nil? value)
         (.equals "" value)
         (identical? value :tech.v3.dataset/missing)
-        (and (string? value) (.equalsIgnoreCase ^String value "na")))))
+        (and (not (:disable-na-as-missing? options))
+             (string? value) (.equalsIgnoreCase ^String value "na")))))
 
 
 (deftype FixedTypeParser [^IMutList container
@@ -210,7 +211,7 @@
       ;;be in the space of the container or it could require the parse-fn
       ;;to make it.
       (let [parsed-value (cond
-                           (missing-value? value)
+                           (missing-value? value {})
                            :tech.v3.dataset/missing
                            (and (identical? (dtype/datatype value) container-dtype)
                                 (not (instance? String value)))
@@ -395,7 +396,7 @@
   (addValue [_p idx value]
     (let [parsed-value
           (cond
-            (missing-value? value)
+            (missing-value? value options)
             :tech.v3.dataset/missing
 
 
@@ -494,7 +495,7 @@
   PParser
   (addValue [_p idx value]
     (set! max-idx idx)
-    (when-not (missing-value? value)
+    (when-not (missing-value? value options)
       (let [val-dtype (fast-dtype value)]
         ;;setup container for new data
         (when-not (identical? container-dtype val-dtype)

test/tech/v3/dataset_test.clj

@@ -1733,6 +1733,13 @@
            (-> (ds/select ds :all vec-of-bools)
                :a)))))
 
+(deftest disable-na-as-missing
+  (let [expected-column ["foo" "NA"]
+        ds1 (ds/->dataset {:a expected-column} {:disable-na-as-missing? true})
+        ds2 (ds/->dataset (for [v expected-column] {:a v}) {:disable-na-as-missing? true})]
+    (is (= expected-column (:a ds1)))
+    (is (= expected-column (:a ds2)))))
+
 (comment
   (require '[criterium.core :as crit])
   (def data (vec (repeatedly 100000 (fn [] {:a (rand-int 20) :b (rand) :c (rand)}))))