Make DataFrame#to_wide fill nil reshaping

lib/red_amber/data_frame_reshaping.rb

@@ -250,7 +250,7 @@ def to_long(*keep_keys, name: :NAME, value: :VALUE)
     #
     # @since 0.2.0
     #
-    def to_wide(name: :NAME, value: :VALUE)
+    def to_wide(name: :NAME, value: :VALUE, fill_missing: false, fill_with: nil)
       name = name.to_sym
       unless keys.include?(name)
         raise DataFrameArgumentError,
@@ -274,6 +274,22 @@ def to_wide(name: :NAME, value: :VALUE)
         h = converts.to_h
         hash[keeps.to_h][h[name].to_s.to_sym] = h[value]
       end
+      if fill_missing
+        names = [].union(*hash.values.collect(&:keys))
+        hash.each_pair do |ns, vs|
+          next if vs.length == names.length
+
+          keys = vs.keys
+          values = vs.values
+          names.each_with_index do |n, i|
+            next if vs.key?(n)
+
+            keys.insert(i, n)
+            values.insert(i, fill_with)
+          end
+          hash[ns] = keys.zip(values).to_h
+        end
+      end
       ks = hash.first[0].keys + hash.first[1].keys
       vs = hash.map { |k, v| k.values + v.values }.transpose
       DataFrame.new(ks.zip(vs))

test/test_data_frame_reshaping.rb

@@ -128,5 +128,20 @@ class DataFrameReshapingTest < Test::Unit::TestCase
       df = @df.rename(NAME: :key1, VALUE: :key2)
       assert_equal @str, df.to_wide(name: :key1, value: :key2).to_s
     end
+
+    test '#to_wide with missing values' do
+      df = DataFrame.new(
+        names: %w[name1 name1 name1 name2 name2 name3 name3 name3],
+        NAME: %w[One Two Three One Three One Two Three],
+        VALUE: [1.1, 2.1, 3.1, 1.2, 3.2, 1.3, 2.3, 3.3]
+      )
+      wide = DataFrame.new(
+        names: %w[name1 name2 name3],
+        One: [1.1, 1.2, 1.3],
+        Two: [2.1, nil, 2.3],
+        Three: [3.1, 3.2, 3.3]
+      )
+      assert_equal wide, df.to_wide(fill_missing: true)
+    end
   end
 end