Adding values to a hash within/over multiple each loops

Question

I have a concept called snapshot which basically stores a snapshot of how data looked at a certain period of time. What I'm building is a method that loops through the snapshots for each events, and builds a small hash outlining the ownership over time for a given shareholder.

  def fetch_ownership_over_time(shareholder, captable)

    @shareholder = Shareholder.find(shareholder.id)
    @captable = Captable.find(captable.id)
    @company = @captable.company.id
    @ownership_over_time = []

    @captable.events.collect(&:snapshot).each do |snapshot|
      parsed_snapshot = JSON.parse(snapshot)

      @ownership_over_time.push(parsed_snapshot["event"]["name"])
      @ownership_over_time.push(parsed_snapshot["event"]["date"])

      parsed_snapshot["shareholders"].each do |shareholder|
        if shareholder["id"] == @shareholder.id

          @ownership_over_time.push(shareholder["ownership_percentage"]) 

        end
      end
    end
    return @ownership_over_time
  end

I then call this method in my view which successfully retrieves the correct values however they are not structured in any way:

["Event 1 ", "2018-11-19", "0.666666666666667", "Event 2 ", "2018-11-19", "0.333333333333333", "4th event ", "2018-11-19", "0.315789473684211"]

What I'd like to do now though is construct my hash so that each separate snapshot event contains a name, date and ownership_percentage.

Perhaps something like this:

ownership_over_time = [
    {
    event_name = "Event 1" #parsed_snapshot["event"]["name"]
    event_date = "20180202" #parsed_snapshot["event"]["date"]
    ownership_percentage = 0.37 #shareholder["ownership_percentage"]
    },
    {
    event_name = "Event 2" #parsed_snapshot["event"]["name"]
    event_date = "20180501" #parsed_snapshot["event"]["date"]
    ownership_percentage = 0.60 #shareholder["ownership_percentage"]
    }
]

My challenge though is that the ["event"]["name"] an ["event"]["date"] attributes I need to fetch when looping over my snapshots i.e. the first loop (.each do |snapshot|) whereas I get my ownership_percentage when looping over shareholders - the second loop (.each do |shareholder|).

So my question is - how can I build this hash in "two" places so I can return the hash with the 3 attributes?

Appreciative of guidance/help - thank you!

EmmanuelB · Accepted Answer · 2018-11-22 17:33:09Z

1

You have to create a new hash for the object and append that hash to the array of objects you are creating.

  def fetch_ownership_over_time(shareholder, captable)

    @shareholder = Shareholder.find(shareholder.id)
    @captable = Captable.find(captable.id)
    @company = @captable.company.id
    @ownership_over_time = []

    @captable.events.collect(&:snapshot).each do |snapshot|
      parsed_snapshot = JSON.parse(snapshot)
      shareholder = parsed_snapshot['shareholders'].select { |s| s['id'] == @shareholder.id }.first

      local_snapshot = {
        'event_name' => parsed_snapshot['event']['name'],
        'event_date' => parsed_snapshot['event']['date'],
        'ownership_percentage' => shareholder.try(:[], "ownership_percentage") || 0
      }

      @ownership_over_time.push local_snapshot
    end
    return @ownership_over_time
  end

Notice that I changed your second loop to a select. As you currently have it, you risk on pushing two percentages if the id is found twice.

EDIT:

Added functionality to use a default value if no shareholder is found.

edited Nov 22, 2018 at 17:33

answered Nov 22, 2018 at 17:04

EmmanuelB

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7 Comments

rock_n_rolla Over a year ago

Great solution! Thank you!

EmmanuelB Over a year ago

Glad it suits your needs, perhaps there is a more efficient way to solve it or a more stylish way to write it, but I'm sure you can take it from here.

rock_n_rolla Over a year ago

For sure - I've been pondering how best to solve this but will push on from here and try refactor a little. Thank you again!

rock_n_rolla Over a year ago

One thing I've run into is that we get a crash if the ownership_percentage is null or none exist. Do you think I should just wrap the entire local_snapshot in an unless not null so that we skip creating that snapshot if so?

EmmanuelB Over a year ago

Or you could give a default value for it when creating the local_snapshot. As it is a percentage, a persona having 0 is probably what you want when none is found: 'ownership_percentage' => shareholder['ownership_percentage'] || 0

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