agrupa linhas por disciplina, considerando as colunas da primeira ocorrência e transformando as notas em colunas/desc_disciplina

saci.rb

#require 'pry'
require 'csv'

data = CSV.read('./resultado_bj.csv',
  encoding: "UTF-8", headers: true,
  header_converters: :symbol, converters: :all,
  col_sep: '|', quote_char: '"'
)
data = data.map(&:to_hash)
result = {}

def transform(hash, new_hash=nil)
  new_hash ||= hash
  hash.tap do |h|
    h[new_hash[:desc_disciplina]] = new_hash[:nota]
    h.delete(:desc_disciplina)
  end
end

data.each do |line|
  mat = line[:matricula]
  if result.key?(mat)
    transform(result[mat], line)
  else
    result[mat] = transform(line)
  end
end

columns = result.values.map(&:keys).flatten.uniq

CSV.open('./resultado_saci.csv', 'wb', quote_char: '"', col_sep: '|') do |csv|
  csv << columns
  result.values.each do |line|
    csv << line.values_at(*columns)
  end
end