If there's two maximum elements of an array? - arrays

Question

In this code if user type 2, two times and 1, two times. Then there's two maximum elements and both Kinder and Twix should be printed. But how ? I probably can do this with if method but this will make my code even longer. Any cool version? Can I do this with just one if?
a = [0, 0, 0,]
b = ["Kinder", "Twix", "Mars"]
while true
input = gets.chomp.to_i
if input == 1
a[0] += 1
elsif input == 2
a[1] += 1
elsif input == 3
a[2] += 1
elsif input == 0
break
end
end
index = a.index(a.max)
chocolate = b[index] if index
print a.max,chocolate

Answer 1

The question really has nothing to do with how the array a is constructed.
def select_all_max(a, b)
mx = a.max
b.values_at(*a.each_index.select { |i| a[i] == mx })
end
b = ["Kinder", "Twix", "Mars"]
p select_all_max [0, 2, 1], b
["Twix"]
p select_all_max [2, 2, 1], b
["Kinder", "Twix"]
See Array#values_at.
This could alternatively be done in a single pass.
def select_all_max(a, b)
b.values_at(
*(1..a.size-1).each_with_object([0]) do |i,arr|
case a[i] <=> arr.last
when 0
arr << i
when 1
arr = [i]
end
end
)
end
p select_all_max [0, 2, 1], b
["Twix"]
p select_all_max [2, 2, 1], b
["Kinder", "Twix"]
p select_all_max [1, 1, 1], b
["Kinder", "Twix", "Mars"]

Answer 2

One way would be as follows:
First, just separate the input-gathering from the counting, so we'll just gather input in this step:
inputs = []
loop do
input = gets.chomp.to_i
break if input.zero?
inputs << input
end
Now we can tally up the inputs. If you have Ruby 2.7 you can simply do counts_by_input = inputs.tally to get { "Twix" => 2, "Kinder" => 2 }. Otherwise, my preferred approach is to use group_by with transform_values:
counts_by_input = inputs.group_by(&:itself).transform_values(&:count)
# => { "Twix" => 2, "Kinder" => 2 }
Now, since we're going to be extracting values based on their count, we want to have the counts as keys. Normally we might invert the hash, but that won't work in this case because it will only give us one value per key, and we need multiple:
inputs_by_count = counts_by_input.invert
# => { 2 => "Kinder" }
# This doesn't work, it removed one of the values
Instead, we can use another group_by and transform_values (the reason I like these methods is because they're very versatile ...):
inputs_by_count = counts_by_input.
group_by { |input, count| count }.
transform_values { |keyvals| keyvals.map(&:first) }
# => { 2 => ["Twix", "Kinder"] }
The transform_values code here is probably a bit confusing, but one important thing to understand is that often times, calling Enumerable methods on hashes converts them to [[key1, val1], [key2, val2]] arrays:
counts_by_input.group_by { |input, count| count }
# => { 2 => [["Twix", 2], ["Kinder", 2]] }
Which is why we call transform_values { |keyvals| keyvals.map(&:first) } afterwards to get our desired format { 2 => ["Twix", "Kinder"] }
Anyway, at this point getting our result is very easy:
inputs_by_count[inputs_by_count.keys.max]
# => ["Twix", "Kinder"]
I know this probably all seems a little insane, but when you get familiar with Enumerable methods you will be able to do this kind of data transformation pretty fluently.
Tl;dr, give me the codez
inputs = []
loop do
input = gets.chomp.to_i
break if input.zero?
inputs << input
end
inputs_by_count = inputs.
group_by(&:itself).
transform_values(&:count).
group_by { |keyvals, count| count }.
transform_values { |keyvals| keyvals.map(&:first) }
top_count = inputs_by_count.keys.max
inputs_by_count[top_count]
# => ["Twix", "Kinder"]

Answer 3

How about something like this:
maximum = a.max # => 2
top_selling_bars = a.map.with_index { |e, i| b[i] if e == maximum }.compact # => ['Kinder', 'Twix']
p top_selling_bars # => ['Kinder', 'Twix']

Answer 4

If you have
a = [2, 2, 0,]
b = ['Kinder', 'Twix', 'Mars']
You can calculate the maximum value in a via:
max = a.max #=> 2
and find all elements corresponding to that value via:
b.select.with_index { |_, i| a[i] == max }
#=> ["Kinder", "Twix"]