How to extract all values from a key that are inside a hash

I ask a user for input, and store it as hashes inside an array. I need to extract the values that share the same key from those hashes. I want to print the names of students that belong to the same cohort like this:

"May cohort students are: Brian, Penelope"
"June cohort students are: Fred, Pedro"

How could I do this? I need help with this method:

def print(students)
  #go through all hashes in 'students' and group them by cohort
  #print each cohort separately
end

so that I can do using map and select:

def input_students
  puts "Please enter the names of the students"
  puts "To finish, just hit return twice"
  students = []
  name = gets.chomp
  puts "In which cohort is this student?"
  cohort = gets.chomp 
  while !name.empty? do
    students << {cohort.to_sym => name}
    name = gets.chomp
    cohort = gets.chomp
  end
  students
end

students = input_students
print(students)

But I get:

"no implicit conversion of Symbol to Integer"

Firstly I suggest to change input_students because the proposal to enter the name and cohort is displayed only once. And user can't understand what ot enter.

Also I suggest to change the return value of this method.

def input_students
  puts "Leave field empty to finish"
  puts

  students = []

  loop do
    puts "Please enter the name of the student"
    name = gets.chomp
    break if name.empty?

    puts "In which cohort is this student?"
    cohort = gets.chomp
    break if cohort.empty?

    students << { cohort: cohort, name: name }
  end

  students
end

def print(students)
  students.
    map { |s| s[:cohort] }.
    uniq.
    each { |c| puts "#{c} cohort students are #{students.
                                                  find_all { |s| s[:cohort] == c }.
                                                  map { |s| s[:name] }.
                                                  join(', ')}" }
end

students = input_students
print(students)

# First we get an array of cohorts of all students.
# The number of elements in the array is equal to the number of students
students.map { |s| s[:cohort] }

# But many students are in the same cohort.
# To avoid this duplication, get rid of duplicates.
students.map { |s| s[:cohort] }.uniq

# Well done. Now we have an array of unique cohorts.
# We can use this to print information about each cohort.
students.map { |s| s[:cohort] }.uniq.each { |c| puts "Cohort information" }

# How to print information? For each cohort certain actions are carried out.

# First, find all the students in this cohort.
students.find_all { |s| s[:cohort] == c }

# We only need the names of these students.
students.find_all { |s| s[:cohort] == c }.map { |s| s[:name] }

# But this is an array of names. Convert it to a string, separated by commas.
students.find_all { |s| s[:cohort] == c }.map { |s| s[:name] }.join(', ')