数组索引

s = np.arange(13)**2
s

array([  0,   1,   4,   9,  16,  25,  36,  49,  64,  81, 100, 121, 144])

s[0], s[4], s[-1]

(0, 16, 144)

s[1:5]

array([ 1,  4,  9, 16])

s[-4:]

array([ 81, 100, 121, 144])

s[-5::-2]

array([64, 36, 16,  4,  0])

r = np.arange(36)
r.resize((6, 6))
r

array([[ 0,  1,  2,  3,  4,  5],
       [ 6,  7,  8,  9, 10, 11],
       [12, 13, 14, 15, 16, 17],
       [18, 19, 20, 21, 22, 23],
       [24, 25, 26, 27, 28, 29],
       [30, 31, 32, 33, 34, 35]])

r[2, 2]

14

r[3, 3:6]

array([21, 22, 23])

r[:2, :-1]

array([[ 0,  1,  2,  3,  4],
       [ 6,  7,  8,  9, 10]])

r[-1, ::2]

array([30, 32, 34])

r[r > 30]

array([31, 32, 33, 34, 35])

r[r > 30] = 30
r

array([[ 0,  1,  2,  3,  4,  5],
       [ 6,  7,  8,  9, 10, 11],
       [12, 13, 14, 15, 16, 17],
       [18, 19, 20, 21, 22, 23],
       [24, 25, 26, 27, 28, 29],
       [30, 30, 30, 30, 30, 30]])