def check_data_items(data_items)
if !data_items || data_items.empty?
raise ArgumentError, "Examples data set must not be empty."
elsif !data_items.first.is_a?(Enumerable)
raise ArgumentError, "Unkown format for example data."
end
attributes_num = data_items.first.length
data_items.each_index do |index|
if data_items[index].length != attributes_num
raise ArgumentError,
"Quantity of attributes is inconsistent. " +
"The first item has #{attributes_num} attributes "+
"and row #{index} has #{data_items[index].length} attributes"
end
end
end