diff --git a/README.md b/README.md
index 64a787f..53cd049 100644
--- a/README.md
+++ b/README.md
@@ -126,6 +126,24 @@ Then, output bocomes as belows (indented). You can see the `message` field is jo
 
     Remove tag suffix for output message
 
+* remove_tag_slice *min..max*
+
+    Remove tag parts by slice function. FYI: This option behaves like `tag.split('.').slice(min..max)`.
+
+    For example,
+
+        remove_tag_slice 0..-2
+
+    changes an input tag `foo.bar.host1` to `foo.bar`. 
+
+* aggregate
+
+    Aggregation unit. One of `all`, `in_tag`, `out_tag` can be specified. Default is `all`.
+
+    * `all` counts summation for all input messages and emit one message in each interval.
+    * `in_tag` counts summation for each input tag seperately. 
+    * `out_tag` counts summation for each tag *modified* by `add_tag_prefix`, `remove_tag_prefix`, or `remove_tag_slice`. 
+
 - delimiter
 
     Output matched messages after `join`ed with the specified delimiter.
diff --git a/lib/fluent/plugin/out_grepcounter.rb b/lib/fluent/plugin/out_grepcounter.rb
index 5c0d3e6..60cfd02 100644
--- a/lib/fluent/plugin/out_grepcounter.rb
+++ b/lib/fluent/plugin/out_grepcounter.rb
@@ -32,6 +32,7 @@ def initialize
   config_param :remove_tag_prefix, :string, :default => nil
   config_param :add_tag_suffix, :string, :default => nil
   config_param :remove_tag_suffix, :string, :default => nil
+  config_param :remove_tag_slice, :string, :default => nil
   config_param :output_with_joined_delimiter, :string, :default => nil # obsolete
   config_param :delimiter, :string, :default => nil
   config_param :aggregate, :string, :default => 'tag'
@@ -94,7 +95,7 @@ def configure(conf)
       end
     end
 
-    if @tag.nil? and @add_tag_prefix.nil? and @remove_tag_prefix.nil? and @add_tag_suffix.nil? and @remove_tag_suffix.nil?
+    if @tag.nil? and @add_tag_prefix.nil? and @remove_tag_prefix.nil? and @add_tag_suffix.nil? and @remove_tag_suffix.nil? and @remove_tag_slice.nil?
       @add_tag_prefix = 'count' # not ConfigError to support lower version compatibility
     end
     @tag_proc = tag_proc
@@ -102,11 +103,14 @@ def configure(conf)
     case @aggregate
     when 'all'
       raise Fluent::ConfigError, "grepcounter: `tag` must be specified with aggregate all" if @tag.nil?
-    when 'tag'
-      # raise Fluent::ConfigError, "grepcounter: add_tag_prefix must be specified with aggregate tag" if @add_tag_prefix.nil?
+    when 'tag' # obsolete
+      @aggregate = 'in_tag'
+    when 'in_tag'
+    when 'out_tag'
     else
-      raise Fluent::ConfigError, "grepcounter: aggregate allows tag/all"
+      raise Fluent::ConfigError, "grepcounter: aggregate allows all/in_tag/out_tag"
     end
+    @aggregate_proc = aggregate_proc(@tag_proc)
 
     if @store_file
       f = Pathname.new(@store_file)
@@ -156,12 +160,14 @@ def emit(tag, es, chain)
         count += 1
       end
     end
+
+    aggregate_key = @aggregate_proc.call(tag)
     # thread safe merge
-    @counts[tag] ||= 0
-    @matches[tag] ||= []
+    @counts[aggregate_key] ||= 0
+    @matches[aggregate_key] ||= []
     @mutex.synchronize do
-      @counts[tag] += count
-      @matches[tag] += matches
+      @counts[aggregate_key] += count
+      @matches[aggregate_key] += matches
     end
 
     chain.next
@@ -192,22 +198,29 @@ def flush_emit(step)
     time = Fluent::Engine.now
     flushed_counts, flushed_matches, @counts, @matches = @counts, @matches, {}, {}
 
-    if @aggregate == 'all'
-      count = 0; matches = []
-      flushed_counts.keys.each do |tag|
-        count += flushed_counts[tag]
-        matches += flushed_matches[tag]
-      end
+    case @aggregate
+    when 'all'
+      count = flushed_counts[:all]
+      matches = flushed_matches[:all]
       output = generate_output(count, matches)
       Fluent::Engine.emit(@tag, time, output) if output
-    else
+    when 'out_tag'
+      flushed_counts.keys.each do |out_tag|
+        count = flushed_counts[out_tag]
+        matches = flushed_matches[out_tag]
+        output = generate_output(count, matches)
+        if output
+          Fluent::Engine.emit(out_tag, time, output)
+        end
+      end
+    else # in_tag
       flushed_counts.keys.each do |tag|
         count = flushed_counts[tag]
         matches = flushed_matches[tag]
         output = generate_output(count, matches, tag)
         if output
-          emit_tag = @tag_proc.call(tag)
-          Fluent::Engine.emit(emit_tag, time, output)
+          out_tag = @tag_proc.call(tag)
+          Fluent::Engine.emit(out_tag, time, output)
         end
       end
     end
@@ -234,7 +247,30 @@ def generate_output(count, matches, tag = nil)
     output
   end
 
+  def aggregate_proc(tag_proc)
+    case @aggregate
+    when 'all'
+      Proc.new {|tag| :all }
+    when 'in_tag'
+      Proc.new {|tag| tag }
+    when 'out_tag'
+      Proc.new {|tag| tag_proc.call(tag) }
+    end
+  end
+
   def tag_proc
+    tag_slice_proc =
+      if @remove_tag_slice
+        lindex, rindex = @remove_tag_slice.split('..', 2)
+        if lindex.nil? or rindex.nil? or lindex !~ /^-?\d+$/ or rindex !~ /^-?\d+$/
+          raise Fluent::ConfigError, "out_grepcounter: remove_tag_slice must be formatted like [num]..[num]"
+        end
+        l, r = lindex.to_i, rindex.to_i
+        Proc.new {|tag| (tags = tag.split('.')[l..r]).nil? ? "" : tags.join('.') }
+      else
+        Proc.new {|tag| tag }
+      end
+
     rstrip = Proc.new {|str, substr| str.chomp(substr) }
     lstrip = Proc.new {|str, substr| str.start_with?(substr) ? str[substr.size..-1] : str }
     tag_prefix = "#{rstrip.call(@add_tag_prefix, '.')}." if @add_tag_prefix
@@ -242,16 +278,16 @@ def tag_proc
     tag_prefix_match = "#{rstrip.call(@remove_tag_prefix, '.')}." if @remove_tag_prefix
     tag_suffix_match = ".#{lstrip.call(@remove_tag_suffix, '.')}" if @remove_tag_suffix
     tag_fixed = @tag if @tag
-    if tag_fixed
-      Proc.new {|tag| tag_fixed }
-    elsif tag_prefix_match and tag_suffix_match
-      Proc.new {|tag| "#{tag_prefix}#{rstrip.call(lstrip.call(tag, tag_prefix_match), tag_suffix_match)}#{tag_suffix}" }
+    if tag_prefix_match and tag_suffix_match
+      Proc.new {|tag| "#{tag_prefix}#{rstrip.call(lstrip.call(tag_slice_proc.call(tag), tag_prefix_match), tag_suffix_match)}#{tag_suffix}" }
     elsif tag_prefix_match
-      Proc.new {|tag| "#{tag_prefix}#{lstrip.call(tag, tag_prefix_match)}#{tag_suffix}" }
+      Proc.new {|tag| "#{tag_prefix}#{lstrip.call(tag_slice_proc.call(tag), tag_prefix_match)}#{tag_suffix}" }
     elsif tag_suffix_match
-      Proc.new {|tag| "#{tag_prefix}#{rstrip.call(tag, tag_suffix_match)}#{tag_suffix}" }
+      Proc.new {|tag| "#{tag_prefix}#{rstrip.call(tag_slice_proc.call(tag), tag_suffix_match)}#{tag_suffix}" }
+    elsif tag_prefix || @remove_tag_slice || tag_suffix
+      Proc.new {|tag| "#{tag_prefix}#{tag_slice_proc.call(tag)}#{tag_suffix}" }
     else
-      Proc.new {|tag| "#{tag_prefix}#{tag}#{tag_suffix}" }
+      Proc.new {|tag| tag_fixed }
     end
   end
 
diff --git a/spec/out_grepcounter_spec.rb b/spec/out_grepcounter_spec.rb
index 8626041..3095c98 100644
--- a/spec/out_grepcounter_spec.rb
+++ b/spec/out_grepcounter_spec.rb
@@ -340,6 +340,16 @@ def delete!(key)
       it { emit }
     end
 
+    context 'remove_tag_slice' do
+      let(:config) { CONFIG + %[remove_tag_slice 0..-2] }
+      let(:tag) { 'syslog.host1' }
+      before do
+        allow(Fluent::Engine).to receive(:now).and_return(time)
+        expect(Fluent::Engine).to receive(:emit).with("syslog", time, expected)
+      end
+      it { emit }
+    end
+
     context 'all tag options' do
       let(:config) { CONFIG + %[
          add_tag_prefix foo
@@ -439,6 +449,45 @@ def delete!(key)
       it { emit }
     end
 
+    context 'aggregate in_tag' do
+      let(:messages) { ['foobar', 'foobar'] }
+      let(:emit) do
+        driver.run { messages.each {|message| driver.emit_with_tag({'message' => message}, time, 'foo.bar') } }
+        driver.run { messages.each {|message| driver.emit_with_tag({'message' => message}, time, 'foo.bar2') } }
+        driver.instance.flush_emit(0)
+      end
+
+      let(:config) { CONFIG + %[aggregate tag \n remove_tag_slice 0..-2] }
+      before do
+        allow(Fluent::Engine).to receive(:now).and_return(time)
+        expect(Fluent::Engine).to receive(:emit).with("foo", time, {
+          "count"=>2, "message"=>["foobar", "foobar"], "input_tag"=>"foo.bar", "input_tag_last"=>"bar"
+        })
+        expect(Fluent::Engine).to receive(:emit).with("foo", time, {
+          "count"=>2, "message"=>["foobar", "foobar"], "input_tag"=>"foo.bar2", "input_tag_last"=>"bar2"
+        })
+      end
+      it { emit }
+    end
+
+    context 'aggregate out_tag' do
+      let(:messages) { ['foobar', 'foobar'] }
+      let(:emit) do
+        driver.run { messages.each {|message| driver.emit_with_tag({'message' => message}, time, 'foo.bar') } }
+        driver.run { messages.each {|message| driver.emit_with_tag({'message' => message}, time, 'foo.bar2') } }
+        driver.instance.flush_emit(0)
+      end
+
+      let(:config) { CONFIG + %[aggregate out_tag \n remove_tag_slice 0..-2] }
+      before do
+        allow(Fluent::Engine).to receive(:now).and_return(time)
+        expect(Fluent::Engine).to receive(:emit).with("foo", time, {
+          "count"=>4, "message"=>["foobar", "foobar", "foobar", "foobar"]
+        })
+      end
+      it { emit }
+    end
+
     context 'replace_invalid_sequence' do
       let(:config) { CONFIG + %[regexp WARN \n replace_invalid_sequence true] }
       let(:messages) { [ "\xff".force_encoding('UTF-8') ] }