Find The Most Frequently Occurring Element In An Array In Ruby
Count element occurrences and return the one that appears most often — useful for analytics, voting systems, and mode calculations.
Description
Use Enumerable#tally (Ruby 2.7+) to count occurrences into a hash, then max_by to find the element with the highest count. For older Ruby, use each_with_object or group_by as alternatives.
For ties (multiple elements share the max count), max_by returns the first one encountered. Use select + max_by to retrieve all tied elements.
Sample input:
votes = [:alice, :bob, :alice, :carol, :bob, :alice]
Sample Output:
:alice # appears 3 times
Answer
votes = [:alice, :bob, :alice, :carol, :bob, :alice]
# Ruby 2.7+ — tally then max_by
votes.tally.max_by { |_, count| count }.first
# => :alice
# Get the count too
votes.tally.max_by { |_, count| count }
# => [:alice, 3]
# Handle ties — return all elements with max count
tally = votes.tally
max_count = tally.values.max
tally.select { |_, count| count == max_count }.keys
# => [:alice] (only alice has 3; for ties would return all tied elements)
# Pre-Ruby 2.7
votes.group_by(&:itself)
.max_by { |_, arr| arr.length }
.first
# => :alice
# Numeric mode
[4, 7, 2, 7, 3, 7, 4].tally.max_by { |_, c| c }.first
# => 7
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