import numpy as np
arr = np.array([
[12.1, -23.9],
[3.91, -20.1],
[2.12, -7.93],
])
arr.size # Nombre d'éléments
6
arr.shape # Dimensions : (3 lignes, 2 colonnes)
(3, 2)
arr2 = arr * 3
arr2
array([[ 36.3 , -71.7 ], [ 11.73, -60.3 ], [ 6.36, -23.79]])
arr.T
array([[ 12.1 , 3.91, 2.12], [-23.9 , -20.1 , -7.93]])
ou aussi
arr * arr2
array([[ 439.23 , 1713.63 ], [ 45.8643, 1212.03 ], [ 13.4832, 188.6547]])
arr.dot(arr2.T)
array([[2152.86 , 1583.103 , 645.537 ], [1583.103 , 1257.8943, 503.0466], [ 645.537 , 503.0466, 202.1379]])
ou aussi
arr @ arr2.T
array([[2152.86 , 1583.103 , 645.537 ], [1583.103 , 1257.8943, 503.0466], [ 645.537 , 503.0466, 202.1379]])
arr[1, 1]
-20.1
# Les valeurs de la 2ème colonne (indice 1),
# sur les deux premières lignes (de l'indice 0 à l 'indice 2, exclu)
arr[0:2, 1]
array([-23.9, -20.1])
arr[arr > 0]
array([12.1 , 3.91, 2.12])
arr.reshape(6, 1)
array([[ 12.1 ], [-23.9 ], [ 3.91], [-20.1 ], [ 2.12], [ -7.93]])
arr.reshape(1, 6)
array([[ 12.1 , -23.9 , 3.91, -20.1 , 2.12, -7.93]])
# Division (inplace) de tous les éléments de la
# deuxième colonne (indice 1) par 3
arr[:,1] /= 3
arr
array([[12.1 , -7.96666667], [ 3.91 , -6.7 ], [ 2.12 , -2.64333333]])
# Un tableau de "zéros"
np.zeros((5, 3))
array([[0., 0., 0.], [0., 0., 0.], [0., 0., 0.], [0., 0., 0.], [0., 0., 0.]])
# Un tableau de "uns"
np.ones((3, 4))
array([[1., 1., 1., 1.], [1., 1., 1., 1.], [1., 1., 1., 1.]])
# Éléments régulièrement espacés
np.linspace(1., 4., 6) # Premier, dernier, nombre d'éléments
array([1. , 1.6, 2.2, 2.8, 3.4, 4. ])
# 100 valeurs entre 0 et 1
np.random.uniform(0, 1, 100)
array([0.63207267, 0.25334413, 0.62003443, 0.03595847, 0.53132963, 0.98929467, 0.55196562, 0.6271361 , 0.78922376, 0.85986802, 0.55022017, 0.34820391, 0.87325921, 0.88120906, 0.0928646 , 0.03215813, 0.76018001, 0.56725939, 0.26273091, 0.73608724, 0.65014426, 0.97053762, 0.21067506, 0.19392623, 0.85192539, 0.84305554, 0.31528744, 0.79967469, 0.20578471, 0.705804 , 0.77886568, 0.21494412, 0.57540145, 0.4377488 , 0.0106107 , 0.08490238, 0.93815511, 0.64729312, 0.10871478, 0.2365647 , 0.02423401, 0.32673054, 0.61410024, 0.30952019, 0.81085005, 0.93957738, 0.81768011, 0.93074419, 0.03303403, 0.55730521, 0.03419084, 0.0299661 , 0.68506768, 0.04243119, 0.96528473, 0.80502653, 0.45657009, 0.84375038, 0.11043918, 0.4457668 , 0.93362206, 0.5987174 , 0.03524744, 0.65094551, 0.70152016, 0.56085846, 0.32847674, 0.56248707, 0.86226929, 0.86645534, 0.34363201, 0.63157005, 0.85027666, 0.67482198, 0.58839083, 0.62920844, 0.70104599, 0.14273936, 0.27463275, 0.52787363, 0.04550776, 0.76649426, 0.42965392, 0.43599553, 0.7679043 , 0.10330457, 0.82464557, 0.85733916, 0.95532237, 0.56893847, 0.98937443, 0.46658664, 0.27754862, 0.24940971, 0.84281207, 0.68464254, 0.97639498, 0.70109829, 0.42213889, 0.65796999])