diff --git a/lib/trifle/stats/formatter/category.rb b/lib/trifle/stats/formatter/category.rb
index 473cb4b..f637a38 100644
--- a/lib/trifle/stats/formatter/category.rb
+++ b/lib/trifle/stats/formatter/category.rb
@@ -6,12 +6,19 @@ class Formatter
       class Category
         Trifle::Stats::Series.register_formatter(:category, self)
 
-        def format(series:, path:)
+        def format(series:, path:, slices: 1, &block)
           keys = path.split('.')
-          series[:at].each_with_object(Hash.new(0)).with_index do |(_at, map), i|
-            series[:values][i].dig(*keys).each do |key, value|
-              k, v = block_given? ? yield(key, value) : [key.to_s, value.to_f]
-              map[k] += v
+          result = series[:at].zip(series[:values].map { |v| v.dig(*keys) || {} })
+          sliced(result: result, slices: slices, block: block)
+        end
+
+        def sliced(result:, slices:, block: nil) # rubocop:disable Metrics/AbcSize
+          result[(result.count - (result.count / slices * slices))..].each_slice(result.count / slices).map do |slice|
+            slice.each_with_object(Hash.new(0)) do |(_at, data), map|
+              data.each do |key, value|
+                k, v = block ? block.call(key, value) : [key.to_s, value.to_f]
+                map[k] += v
+              end
             end
           end
         end
diff --git a/lib/trifle/stats/formatter/timeline.rb b/lib/trifle/stats/formatter/timeline.rb
index 35d76e8..b7647bc 100644
--- a/lib/trifle/stats/formatter/timeline.rb
+++ b/lib/trifle/stats/formatter/timeline.rb
@@ -6,11 +6,17 @@ class Formatter
       class Timeline
         Trifle::Stats::Series.register_formatter(:timeline, self)
 
-        def format(series:, path:)
+        def format(series:, path:, slices: 1, &block)
           keys = path.split('.')
-          series[:at].map.with_index do |at, i|
-            value = series[:values][i].dig(*keys)
-            block_given? ? yield(at, value) : [at, value.to_f]
+          result = series[:at].zip(series[:values].map { |v| v.dig(*keys) })
+          sliced(result: result, slices: slices, block: block)
+        end
+
+        def sliced(result:, slices:, block: nil)
+          result[(result.count - (result.count / slices * slices))..].each_slice(result.count / slices).map do |slice|
+            slice.map do |at, value|
+              block ? block.call(at, value) : [at, value.to_f]
+            end
           end
         end
       end