How to skip over null values in Ruby hashes - ruby-on-rails

Question

I have an array in which each array item is a hash with date values, as shown in my example below. In actuality, it is longer and there are about 20 dates per item instead of 3. What I need to do is get the date interval values for each item (that is, how many days between each date value), and their intervals' medians. My code is as follows:
require 'csv'
require 'date'
dateArray = [{:date_one => "May 1", :date_two =>"May 5", :date_three => " "}, {:date_one => "May 10", :date_two =>"May 10", :date_three => "May 20"}, {:date_one => "May 6", :date_two =>"May 11", :date_three => "May 12"}]
public
def median
sorted = self.sort
len = sorted.length
return (sorted[(len - 1) / 2] + sorted[len / 2]) / 2.0
end
puts dateIntervals = dateArray.map{|h| (DateTime.parse(h[:date_two]) - DateTime.parse(h[:date_one])).to_i}
puts "\nMedian: "
puts dateIntervals.median
Which returns these date interval values and this median:
4
0
5
Median: 4
However, some of these items' values are empty, as in the first item, in its :date_three value. If I try to run the same equations for the :date_three to :date_two values, as follows, it will throw an error because the last :date_three value is empty.
It's okay that I can't get that interval, but I would still would need the next two items date intervals (which would be 10 and 1).
How can I skip over intervals that return errors when I try to run them?

Answer 1

I would recommend adding helper functions that can deal with the types of inputs you're expecting. For instance:
def date_diff(date_one, date_two)
return nil if date_one.nil? || date_two.nil?
(date_one - date_two).to_i
end
def str_to_date(input_string)
DateTime.parse(input_string)
rescue
nil
end
dateArray.map{|h| date_diff(str_to_date(h[:date_three]), str_to_date(h[:date_two])) }
=> [nil, 10, 1]
dateArray.map{|h| date_diff(str_to_date(h[:date_three]), str_to_date(h[:date_two])) }.compact.median
=> 5.5
The bonus here is that you can then add unit tests for the individual components so that you can easily test edge cases (nil dates, empty string dates, etc).

Answer 2

In your map block, you can just add a check to make sure the values aren't blank
dateIntervals = dateArray.map{ |h|
(DateTime.parse(h[:date_two]) - DateTime.parse(h[:date_one])).to_i unless any_blank?(h)
}
def any_blank?(h)
h.each do |k, v|
return true if v == " "
end
end

Answer 3

I would first just filter out the empty values first (I check if the string consists entirely of whitespace or is empty), then compare the remaining values using your existing code. I added a loop which will compare all values in the sequence to the next value.
dateArray = [
{ date_one: "May 1", date_two: "May 5", date_three: " ", date_four: "" },
{ date_one: "May 10", date_two: "May 10", date_three: "May 20" }
]
intervals = dateArray.map do |hash|
filtered = hash.values.reject { |str| str =~ /^\s*$/ }
(0...filtered.size-1).map { |idx| (DateTime.parse(filtered[idx+1]) - DateTime.parse(filtered[idx])).to_i }
end
# => [[4], [0, 10]]