:json format keeps empty attribute columns

src/main/clojure/conexp/io/contexts.clj

@@ -329,7 +329,10 @@
 (add-context-input-format :csv
                           (fn [rdr]
                             (try
-                              (re-matches #"^[^,]+,[^,]+$" (read-line))
+                              (let [first-line (read-line)]
+                                (and (re-matches #"^[^,]+,[^,]+$" first-line)
+                                     ;; do not read empty json context as csv
+                                     (not= first-line "{\"attributes\":[],\"adjacency-list\":[]}")))
                               (catch Exception _))))
 
 (define-context-input-format :csv
@@ -624,11 +627,13 @@
   "Returns a formal context as a map that can easily be converted into json format.
 
   Example:
-  {formal_context: {
-     object: \"b\",
-     attributes: [\"1\", \"2\"]}}"
+  {:attributes (\"1\", \"2\")
+   :adjacency-list 
+     [{:object \"b\",
+       :attributes (\"1\", \"2\")}]}"
   [ctx]
-  {:formal_context 
+  {:attributes (into () (attributes ctx))
+   :adjacency-list 
      (mapv (partial object->json ctx) (objects ctx))})
 
 (defn- json-ctx->incidence
@@ -639,9 +644,10 @@
 (defn json->ctx
   "Returns a Context object for the given json context."
   [json-ctx]
-  (let [objects (map :object json-ctx)
-        attributes (distinct (flatten (map :attributes json-ctx)))
-        incidence (apply union (mapv json-ctx->incidence json-ctx))]
+  (let [attributes (:attributes json-ctx)
+        ctx-list (:adjacency-list json-ctx)
+        objects (map :object ctx-list)
+        incidence (apply union (mapv json-ctx->incidence ctx-list))]
     (make-context objects attributes incidence)))
 
 ;; Json Format (src/main/resources/schemas/context_schema_v1.0.json)
@@ -660,7 +666,7 @@
   [file]
   (with-in-reader file 
     (let [file-content (json/read *in* :key-fn keyword)
-          json-ctx (:formal_context file-content)
+          json-ctx file-content
           schema-file "src/main/resources/schemas/context_schema_v1.0.json"]
       (assert (matches-schema? file-content schema-file)
               (str "The input file does not match the schema given at " schema-file "."))

src/main/clojure/conexp/io/fcas.clj

@@ -44,7 +44,7 @@
   (let [json-ctx (:context json-fca)
         json-lattice (:lattice json-fca)
         json-implication-sets (:implication_sets json-fca)]
-    (cond-> {:context (json->ctx (:formal_context json-ctx))}
+    (cond-> {:context (json->ctx json-ctx)}
       (some? json-lattice) (assoc :lattice (json->lattice json-lattice))
       (some? json-implication-sets) (assoc :implication-sets (map json->implications json-implication-sets)))))
 

src/main/resources/schemas/context_schema_v1.0.json

@@ -28,10 +28,18 @@
     }
   },
   "required": [
-    "formal_context"
+    "attributes",
+    "adjacency-list"
   ],
   "properties": {
-    "formal_context": {
+    "attributes": {
+      "type": "array",
+      "description": "List of all attributes",
+      "items": {
+        "$ref": "fca_schema_v1.0.json#/$defs/attribute"
+      }
+    },
+    "adjacency-list": {
       "type": "array",
       "items": {
         "$ref": "#/$defs/context_item"

src/test/clojure/conexp/io/contexts_test.clj

@@ -230,6 +230,13 @@
                       fmt #{:fcalgs}]
     (= ctx (out-in-without-format ctx 'context fmt))))
 
-;;;
+(deftest test-ctx->json
+  ;; test that attributes with empty column are not dropped
+  (let [K (make-context-from-matrix [1 2] [:a :b] [1 0 0 0])]
+    (is (= (ctx->json K)
+           {:attributes '(:a :b)
+            :adjacency-list
+            [{:object 1, :attributes '(:a)}
+             {:object 2, :attributes '()}]}))))
 
 nil

testing-data/digits-context.json

@@ -1 +1 @@
-{"formal_context":[{"object":"9","attributes":["d","f","a","b","g"]},{"object":"3","attributes":["f","a","b","g","c"]},{"object":"4","attributes":["d","f","b","g"]},{"object":"8","attributes":["d","f","e","a","b","g","c"]},{"object":"7","attributes":["f","a","g"]},{"object":"5","attributes":["d","a","b","g","c"]},{"object":"6","attributes":["d","e","b","g","c"]},{"object":"1","attributes":["f","g"]},{"object":"0","attributes":["d","f","e","a","g","c"]},{"object":"2","attributes":["f","e","a","b","c"]}]}
+{"attributes":["a","b","c","d","e","f","g"],"adjacency-list":[{"object":"9","attributes":["d","f","a","b","g"]},{"object":"3","attributes":["f","a","b","g","c"]},{"object":"4","attributes":["d","f","b","g"]},{"object":"8","attributes":["d","f","e","a","b","g","c"]},{"object":"7","attributes":["f","a","g"]},{"object":"5","attributes":["d","a","b","g","c"]},{"object":"6","attributes":["d","e","b","g","c"]},{"object":"1","attributes":["f","g"]},{"object":"0","attributes":["d","f","e","a","g","c"]},{"object":"2","attributes":["f","e","a","b","c"]}]}

testing-data/digits-fca.json

@@ -1,6 +1,7 @@
 {
   "context": {
-    "formal_context": [
+    "attributes": ["a","b","c","d","e","f","g"],
+    "adjacency-list": [
       {
         "object": "9",
         "attributes": [