配列を渡すと、先頭からブロック内の条件に一致する要素を返し、同時に配列から取り除くメソッド

01_input.csv

02_result.csv

shift_by.rb

require 'csv'
require 'pp'

array_of_rows = CSV.parse(DATA, :headers => true).map {|row| row }

def shift_by(array, &block)
  i = array.each_with_index.each_with_object(nil) do |(item, index), n|
    break index unless block.call(item)
  end
  i ? array.shift(i) : array.slice!(0..-1)
end

array_of_rows
  .map! {|row| row['session'] = "#{row['ｴｰｼﾞｪﾝﾄ']}_#{row['ﾛｸﾞｵﾝﾕｰｻﾞｰ']}"; row }
  .sort_by! {|row| [row['ｴｰｼﾞｪﾝﾄ'], row['日付'], row['ｲﾍﾞﾝﾄ時刻']] }

out = []
until array_of_rows.size.zero?
  out << shift_by(array_of_rows) {|row| row['session'] == array_of_rows.first['session'] }
end

table = out.map do |ary|
  ary.first['終了時刻'] = ary.last['ｲﾍﾞﾝﾄ時刻'];
  ary.first.delete('session')
  ary.first
end

table.sort_by! {|row| [row['日付'], row['ｲﾍﾞﾝﾄ時刻'], row['終了時刻']] }

puts CSV::Table.new(table).to_csv

__END__
ｴｰｼﾞｪﾝﾄ,ﾛｸﾞｵﾝﾕｰｻﾞｰ,日付,ｲﾍﾞﾝﾄ時刻
PC_A,UserA,2000/01/01,00:00:00
PC_A,UserA,2000/01/01,01:00:00
PC_A,UserA,2000/01/01,02:00:00
PC_C,UserA,2000/01/01,02:30:00
PC_C,UserA,2000/01/01,03:00:00
PC_A,UserB,2000/01/01,04:00:00
PC_C,UserA,2000/01/01,04:30:00
PC_A,UserB,2000/01/01,05:00:00
PC_A,UserB,2000/01/01,06:00:00