The simplest way to group by:

  • day
  • week
  • hour of the day
  • and more (complete list below)

:tada: Time zones - including daylight saving time - supported!! the best part

:cake: Get the entire series - the other best part

Supports PostgreSQL, MySQL, and Redshift, plus arrays and hashes (and limited support for SQLite)

:cupid: Goes hand in hand with Chartkick

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# {
#   Sat, 28 May 2016 => 50,
#   Sun, 29 May 2016 => 100,
#   Mon, 30 May 2016 => 34
# }

Results are returned in ascending order by default, so no need to sort.

You can group by:

  • second
  • minute
  • hour
  • day
  • week
  • month
  • quarter
  • year


  • hour_of_day
  • day_of_week (Sunday = 0, Monday = 1, etc)
  • day_of_month
  • month_of_year

Use it anywhere you can use group. Works with count, sum, minimum, maximum, and average. For median, check out ActiveMedian. For other aggregate functions, including multiple together, check out CalculateAll.

Time Zones

The default time zone is Change this with:

Groupdate.time_zone = "Pacific Time (US & Canada)"


User.group_by_week(:created_at, time_zone: "Pacific Time (US & Canada)").count
# {
#   Sun, 06 Mar 2016 => 70,
#   Sun, 13 Mar 2016 => 54,
#   Sun, 20 Mar 2016 => 80
# }

Time zone objects also work. To see a list of available time zones in Rails, run rake time:zones:all.

Week Start

Weeks start on Sunday by default. Change this with:

Groupdate.week_start = :mon # first three letters of day


User.group_by_week(:created_at, week_start: :mon).count

Day Start

You can change the hour days start with:

Groupdate.day_start = 2 # 2 am - 2 am


User.group_by_day(:created_at, day_start: 2).count

Time Range

To get a specific time range, use:

User.group_by_day(:created_at, range:

To get the most recent time periods, use:

User.group_by_week(:created_at, last: 8).count # last 8 weeks

To exclude the current period, use:

User.group_by_week(:created_at, last: 8, current: false).count


You can order in descending order with:

User.group_by_day(:created_at, reverse: true).count


Keys are returned as date or time objects for the start of the period.

To get keys in a different format, use:

User.group_by_month(:created_at, format: "%b %Y").count
# {
#   "Jan 2015" => 10
#   "Feb 2015" => 12
# }


User.group_by_hour_of_day(:created_at, format: "%-l %P").count
# {
#    "12 am" => 15,
#    "1 am"  => 11
#    ...
# }

Takes a String, which is passed to strftime, or a Symbol, which is looked up by I18n.localize in i18n scope 'time.formats', or a Proc. You can pass a locale with the locale option.


The entire series is returned by default. To exclude points without data, use:

User.group_by_day(:created_at, series: false).count

Or change the default value with:

User.group_by_day(:created_at, default_value: "missing").count

Dynamic Grouping

User.group_by_period(:day, :created_at).count

Limit groupings with the permit option.

User.group_by_period(params[:period], :created_at, permit: ["day", "week"]).count

Raises an ArgumentError for unpermitted periods.

Date Columns

If grouping on date columns which don’t need time zone conversion, use:

User.group_by_week(:created_on, time_zone: false).count

User Input

If passing user input as the column, be sure to sanitize it first like you must with group.

column = params[:column]

# check against permitted columns
raise "Unpermitted column" unless ["column_a", "column_b"].include?(column)


Arrays and Hashes

users.group_by_day { |u| u.created_at } # or group_by_day(&:created_at)

Supports the same options as above

users.group_by_day(time_zone: time_zone) { |u| u.created_at }


Hash[ users.group_by_day { |u| u.created_at }.map { |k, v| [k, v.size] } ]


Add this line to your application’s Gemfile:

gem 'groupdate'


Time zone support must be installed on the server.

mysql_tzinfo_to_sql /usr/share/zoneinfo | mysql -u root mysql

or copy and paste these statements into a SQL console.

You can confirm it worked with:

SELECT CONVERT_TZ(NOW(), '+00:00', 'Pacific/Honolulu');

It should return the time instead of NULL.

For SQLite

Groupdate has limited support for SQLite.

  • No time zone support
  • No day_start or week_start options
  • No group_by_quarter method

If your application’s time zone is set to something other than Etc/UTC (the default), create an initializer with:

Groupdate.time_zone = false



Groupdate 4.0 brings a number of improvements. Here are a few to be aware of:

  • group_by methods return an ActiveRecord::Relation instead of a Groupdate::Series
  • Invalid options now throw an ArgumentError
  • week_start now affects day_of_week
  • Custom calculation methods are supported by default


Groupdate 3.0 brings a number of improvements. Here are a few to be aware of:

  • Date objects are now returned for day, week, month, quarter, and year by default. Use dates: false for the previous behavior, or change this globally with Groupdate.dates = false.
  • Array and hash methods no longer return the entire series by default. Use series: true for the previous behavior.
  • The series: false option now returns the correct type and order, and plays nicely with other options.


Groupdate 2.0 brings a number of improvements. Here are two things to be aware of:

  • the entire series is returned by default
  • ActiveSupport::TimeWithZone keys are now returned for every database adapter - adapters previously returned Time or String keys


View the changelog

Groupdate follows Semantic Versioning


Everyone is encouraged to help improve this project. Here are a few ways you can help: