SpecialistOff.NET / Вопросы / Статьи / Фрагменты кода / Резюме / Метки / Помощь / Файлы

Nested Comprehensions

Метки: python

An identity matrix of size n is an n by n square matrix with ones on the main diagonal and zeros elsewhere. A 3 by 3 identity matrix is:

In python we can represent such a matrix by a list of lists, where each sub-list represents a row. A 3 by 3 matrix would be represented by the following list:

[ [ 1, 0, 1 ],
  [ 0, 1, 0 ],
  [ 0, 0, 1 ] ]

The above matrix can be generated by the following comprehension:

[ [ 1 if item_idx == row_idx else 0 for item_idx in range(0, 3) ] for row_idx in range(0, 3) ]