Simplify self preferences

lib/scholar/cluster/affinity_propagation.ex

@@ -42,8 +42,15 @@ defmodule Scholar.Cluster.AffinityPropagation do
       """
     ],
     self_preference: [
-      type: {:or, [:float, :boolean, :integer]},
-      doc: "Self preference."
+      type: :float,
+      doc: """
+      Preferences for each point - points with larger values of preferences
+      are more likely to be chosen as exemplars. The number of clusters is
+      influenced by this option. If the preferences are not passed as arguments,
+      they will be set to the median of the input similarities (resulting in a
+      moderate number of clusters). For a smaller amount of clusters, this can
+      be set to the minimum value of the similarities.
+      """
     ],
     key: [
       type: {:custom, Scholar.Options, :key, []},
@@ -117,7 +124,6 @@ defmodule Scholar.Cluster.AffinityPropagation do
   """
   deftransform fit(data, opts \\ []) do
     opts = NimbleOptions.validate!(opts, @opts_schema)
-    opts = Keyword.update(opts, :self_preference, false, fn x -> x end)
     key = Keyword.get_lazy(opts, :key, fn -> Nx.Random.key(System.system_time()) end)
     fit_n(data, key, NimbleOptions.validate!(opts, @opts_schema))
   end
@@ -337,19 +343,12 @@ defmodule Scholar.Cluster.AffinityPropagation do
 
   defnp initialize_similarities(data, opts \\ []) do
     n = Nx.axis_size(data, 0)
-    self_preference = opts[:self_preference]
-
     dist = -Scholar.Metrics.Distance.pairwise_squared_euclidean(data)
 
     fill_in =
-      cond do
-        self_preference == false ->
-          Nx.broadcast(Nx.median(dist), {n})
-
-        true ->
-          if Nx.size(self_preference) == 1,
-            do: Nx.broadcast(self_preference, {n}),
-            else: self_preference
+      case opts[:self_preference] do
+        nil -> Nx.broadcast(Nx.median(dist), {n})
+        self_preference -> Nx.broadcast(self_preference, {n})
       end
 
     s_modified = dist |> Nx.put_diagonal(fill_in)