Ruby - group_by month for current year, including months with no data

Question

I'm trying to write a method to return a very specific data structure for a chart that I am populating.

A user can enter dates for miles that they've hiked, so on the Mile model I have start_date and end_date attributes.

The method I have currently is close , however it should return a 0 for the current month because the user hasn't entered any miles hiked for the month of May. I also need to constrain it to the current year, which it currently is not.

Here is what my current method looks like:

def miles_by_month
    miles = self.miles.from_this_year.group_by { |t| t.start_date.strftime('%b') }
    total_miles = miles.map do |m|
        { 'indicator': m[0], 'total': m[1].sum(&:length) }
    end
    total_miles
end

And the 'from_this_year' scope on the Mile model if it's helpful:

scope :from_this_year, lambda { where("start_date > ? AND start_date < ?", Time.now.beginning_of_year, Time.now.end_of_year) }

And here is an example of what it returns:

[
    [0] {
        :indicator => "Jan",
            :total => 15
    },
    [1] {
        :indicator => "Feb",
            :total => 10
    },
    [2] {
        :indicator => "Mar",
            :total => 10
    },
    [3] {
        :indicator => "Apr",
            :total => 100
    },
    [4] {
        :indicator => "May",    # I need [4] to show up with 
        :total => 0             # a total of 0. [4] currently
    }                           # does not show up at all.
]

"Indicator" refers to the name of the month, and "total" refers to a sum of the number of miles that user has hiked for that specific month.

Any suggestions?

UPDATE 1

I have modified my miles_by_month method somewhat based on an answer here to the following:

def miles_by_month
    months = Date::ABBR_MONTHNAMES[1..12]
    miles = self.miles.from_this_year.group_by { |t| t.start_date.strftime('%b') }

    total_miles = miles.map do |m|
        { 'indicator': m[0], 'total': m[1].sum(&:length) }
    end

    months.each do |month|
      unless total_miles.any? { |r| r[:indicator] == month }
        total_miles.push(indicator: month, total: 0)
      end
    end

    total_miles
  end

The only remaining thing I need to do is figure out how to constrain the months variable from the start of the year to the current month.

Answer 1

You can do this by looping over each of the months and setting a default value, for example:

MONTHS = Date::ABBR_MONTHNAMES[1..12]

# put this somewhere
MONTHS.each do |month|
  unless results.any? { |r| r[:indicator] == month }
    results.push(indicator: month, total: 0)
  end
end

# you can sort them chronologically if needed
results.sort_by! { |r| MONTHS.index(r[:indicator]) }

Note this is not the most efficient code - it has some O(N^2) stuff which can be optimized to O(N) - but it should hopefully give you a starting point

Answer 2

Based on Max Pleaner's answer, I was able to come up with the following method to correctly return what I needed:

def miles_by_month
    cur_month = Time.now.month
    months = Date::ABBR_MONTHNAMES[1..cur_month]
    miles = self.miles.from_this_year.group_by { |t| t.start_date.strftime('%b') }

    total_miles = miles.map do |m|
        { 'indicator': m[0], 'total': m[1].sum(&:length) }
    end

    months.each do |month|
      unless total_miles.any? { |r| r[:indicator] == month }
        total_miles.push(indicator: month, total: 0)
      end
    end

    total_miles
  end

This returns a data structure like the following:

[
    [0] {
        :indicator => "Jan",
            :total => 15
    },
    [1] {
        :indicator => "Feb",
            :total => 10
    },
    [2] {
        :indicator => "Mar",
            :total => 10
    },
    [3] {
        :indicator => "Apr",
            :total => 100
    },
    [4] {
        :indicator => "May",
            :total => 0
    }
]

It's certainly not the most efficient method and I'd be very curious to see if anyone has more efficient ways of handling this.