Numpyについてのメモ

float からintへ

>>> x = np.array([1.1, 3.5, 4.8])
>>> x.astype(np.int)
array([1, 3, 4])

配列をランダムでシャッフル random.shuffle

>>> datas = np.arange(100)
>>> datas
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, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50,
       51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67,
       68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84,
       85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99])

>>> np.random.shuffle(datas)

>>> datas
array([41, 36, 80, 33, 19, 67, 10, 92, 12, 52, 42, 37, 88, 57,  5, 96, 64,
       74, 86, 51, 94, 69, 30, 95, 40, 78,  0, 18, 21, 45, 99, 58,  6, 49,
        3, 76, 48, 54, 15, 32, 60, 14, 17, 63, 13, 53, 38, 65, 11,  4, 97,
       84, 79, 27,  7, 93, 24, 72,  2, 90, 55, 20, 91, 61, 77, 22, 29,  9,
       68, 47, 35, 87, 50, 70, 98, 26, 23, 75, 83, 34, 44, 28, 25, 59, 71,
       85, 62, 82, 89, 31, 43, 66,  8, 16, 39, 56,  1, 46, 73, 81])

ones , zeros

>>> np.ones((3,1))
array([[1.],
       [1.],
       [1.]])

>>> np.zeros((3,2))
array([[0., 0.],
       [0., 0.],
       [0., 0.]])

>>> np.c_[np.ones((3,1)),np.zeros((3,2))]
array([[1., 0., 0.],
       [1., 0., 0.],
       [1., 0., 0.]])

各軸で取り出し

行で取り出し

>>> datas = np.array([[0,1],[2,3],[4,5]])
>>> datas[0]
array([0, 1])

列で取り出し

>>> datas = np.array([[0,1],[2,3],[4,5]])
>>> datas[:,0]
array([0, 2, 4])

連結:np.r, np.c

>>> import numpy as np

>>> A = np.array([[1,2], [3,4]])
>>> B = np.array([[0,0], [0,0]])
>>> np.r_[A, B]
array([[1, 2],
       [3, 4],
       [0, 0],
       [0, 0]])
>>> np.c_[A, B]
array([[1, 2, 0, 0],
       [3, 4, 0, 0]])

unique:配列の要素をカウントする

>>> arr = [0,0,1]
>>> uni, counts = np.unique(arr,return_counts=True)
>>> uni
array([0, 1])
>>> counts
array([2, 1])

random

permutaion(並べ替え)

名前の通り、数値の並べ替えを行うメソッド。
引数が整数なら、0から引数までの整数をランダムで並べ替えたnumpy.arrayを返す

>>> np.random.permutation(10)
array([8, 3, 7, 9, 1, 0, 4, 6, 2, 5])

引数が配列なら配列をランダムで並べ替えたnumpy.arrayを返す

>>> np.random.permutation([1,2,3,4,5,6])
array([4, 2, 3, 5, 6, 1])
>>> %history -p -o

• 参考文献:document