a = FasterCSV.read("meta_docs/verticals_plus_reasons.csv")

# Largest row
size = a.max { |r1, r2| r1.size <=> r2.size }.size

# Enlarge matrix inserting nils as needed
a.each { |r| r[size - 1] ||= nil }

# So now a == [[1, 2, 3], [3, 4, nil]]
aa = a.transpose

FasterCSV.open("meta_docs/vertials_plus_reasons_transposed.csv", "w+") do |csv|
  aa.each {|row|
    csv << row
  }
end