类型转换、基本内置函数

numpy转列表tolist()

  1. data = np.full((2, 2), np.nan)
  2. data = np.full((2, 2), np.inf)

np.where

numpy.where()分两种调用方式:
1、一个参数np.where(arry):输出arry中‘真’值的坐标(‘真’也可以理解为非零)
2、三个参数np.where(cond,x,y):满足条件(cond)）输出x，不满足输出y

  1. If all the arrays are 1-D, where is equivalent to:
  2. [xv if c else yv
  3.  for c, xv, yv in zip(condition, x, y)]
  1. a = np.arange(10)
  2. array([0, 1, 2, 3, 4, 5, 6, 7, 8, 9])
  3. np.where(a < 5, a)
  4. array([ 0,  1,  2,  3,  4)
  5. np.where(a < 5, a, 10*a)
  6. array([ 0,  1,  2,  3,  4, 50, 60, 70, 80, 90])

np.zeros

zeros(shape, dtype=float, order=’C’)
order:可选参数，c代表与c语言类似，行优先；F代表列优先
np.zeros(5)
array([ 0., 0., 0., 0., 0.])
np.zeros((5,), dtype=np.int)
array([0, 0, 0, 0, 0])

np.argmax(a)

取出a中元素最大值所对应的索引

np.argsort

numpy - 图1

np.partition, np.argpartition

numpy - 图2

np.flip

反转，reverse

快速生成onehot向量

Y = np.eye(100)[Y]

np.concatente

  1. a = np.array([[1, 2], [3, 4]])
  2. b = np.array([[5, 6]])
  3. np.concatenate((a, b), axis=0)
  4. array([[1, 2],
  5.        [3, 4],
  6.        [5, 6]])
  7. np.concatenate((a, b.T), axis=1)
  8. array([[1, 2, 5],
  9.        [3, 4, 6]])
  10. np.concatenate((a, b), axis=None)
  11. array([1, 2, 3, 4, 5, 6])

np.stack

第一个参数为列表，且各元素都是一维数组

  1. arrays = [np.random.randn(3, 4) for _ in range(10)]
  2. np.stack(arrays, axis=0).shape
  3. (10, 3, 4)
  1. a = np.array([1, 2, 3])
  2. b = np.array([2, 3, 4])
  3. np.stack((a, b))
  4. array([[1, 2, 3],
  5.        [2, 3, 4]])

reshape(shape, order=’C’)

order:可选参数，c代表与c语言类似，行优先；F代表列优先
原来的行变成新的行，原来的列变成新的列

Numpy随机数, np.random.xxx

  1. 原来格式为表格（table），转换较复杂，未转换，需要手动复制一下
  2. {"cells":[{"textAlign":"left","verticalAlign":"middle","wrap":true,"backColor":"rgb(250, 250, 250)","value":"函数名称"},{"textAlign":"left","verticalAlign":"middle","wrap":true,"backColor":"rgb(250, 250, 250)","value":"函数功能"},{"textAlign":"left","verticalAlign":"middle","wrap":true,"backColor":"rgb(250, 250, 250)","value":"参数说明"},{"textAlign":"left","verticalAlign":"middle","wrap":true,"backColor":"rgb(238, 238, 238)","value":"rand(d0, d1, …, dn)"},{"textAlign":"left","verticalAlign":"middle","wrap":true,"backColor":"rgb(238, 238, 238)","value":"在[0,1)中产生均匀分布的随机数"},{"textAlign":"left","verticalAlign":"middle","wrap":true,"backColor":"rgb(238, 238, 238)","value":"dn为第n维数据的维度"},{"textAlign":"left","verticalAlign":"middle","wrap":true,"backColor":"rgb(238, 238, 238)","value":"randn(d0, d1, …, dn)"},{"textAlign":"left","verticalAlign":"middle","wrap":true,"backColor":"rgb(238, 238, 238)","value":"产生标准正态分布随机数"},{"textAlign":"left","verticalAlign":"middle","wrap":true,"backColor":"rgb(238, 238, 238)","value":"dn为第n维数据的维度"},{"textAlign":"left","verticalAlign":"middle","wrap":true,"backColor":"rgb(238, 238, 238)","value":"randint(low[, high, size, dtype])"},{"textAlign":"left","verticalAlign":"middle","wrap":true,"backColor":"rgb(238, 238, 238)","value":"产生随机整数"},{"textAlign":"left","verticalAlign":"middle","wrap":true,"backColor":"rgb(238, 238, 238)","value":"low：最小值；high：最大值；size：数据个数，不包括high"},{"textAlign":"left","verticalAlign":"middle","wrap":true,"backColor":"rgb(238, 238, 238)","value":"random_sample([size])"},{"textAlign":"left","verticalAlign":"middle","wrap":true,"backColor":"rgb(238, 238, 238)","value":"在[0,1）内产生均匀分布随机数"},{"textAlign":"left","verticalAlign":"middle","wrap":true,"backColor":"rgb(238, 238, 238)","value":"size：随机数的shape，可以为元祖或者列表，[2,3]表示2维随机数，维度为（2,3）"},{"textAlign":"left","verticalAlign":"middle","wrap":true,"backColor":"rgb(238, 238, 238)","value":"random([size])"},{"textAlign":"left","verticalAlign":"middle","wrap":true,"backColor":"rgb(238, 238, 238)","value":"同random_sample([size])"},{"textAlign":"left","verticalAlign":"middle","wrap":true,"backColor":"rgb(238, 238, 238)","value":"同random_sample([size])"},{"textAlign":"left","verticalAlign":"middle","wrap":true,"backColor":"rgb(238, 238, 238)","value":"ranf([size])"},{"textAlign":"left","verticalAlign":"middle","wrap":true,"backColor":"rgb(238, 238, 238)","value":"同random_sample([size])"},{"textAlign":"left","verticalAlign":"middle","wrap":true,"backColor":"rgb(238, 238, 238)","value":"同random_sample([size])"},{"textAlign":"left","verticalAlign":"middle","wrap":true,"backColor":"rgb(238, 238, 238)","value":"sample([size]))"},{"textAlign":"left","verticalAlign":"middle","wrap":true,"backColor":"rgb(238, 238, 238)","value":"同random_sample([size])"},{"textAlign":"left","verticalAlign":"middle","wrap":true,"backColor":"rgb(238, 238, 238)","value":"同random_sample([size])"},{"textAlign":"left","verticalAlign":"middle","wrap":true,"backColor":"rgb(238, 238, 238)","value":"choice(a[, size, replace, p])"},{"textAlign":"left","verticalAlign":"middle","wrap":true,"backColor":"rgb(238, 238, 238)","value":"从a中随机选择指定数据"},{"textAlign":"left","verticalAlign":"middle","wrap":true,"backColor":"rgb(238, 238, 238)","value":"a：1维数组 size：返回数据形状"},{"textAlign":"left","verticalAlign":"middle","wrap":true,"backColor":"rgb(238, 238, 238)","value":"bytes(length)"},{"textAlign":"left","verticalAlign":"middle","wrap":true,"backColor":"rgb(238, 238, 238)","value":"返回随机位"},{"textAlign":"left","verticalAlign":"middle","wrap":true,"backColor":"rgb(238, 238, 238)","value":"length：位的长度"}],"heights":[40,40,40,40,40,40,40,40,40,40],"widths":[204,181,226]}

乘法

原来格式为表格（table），转换较复杂，未转换，需要手动复制一下
{"cells":[{"textAlign":"center","verticalAlign":"middle","value":""},{"textAlign":"center","verticalAlign":"middle","value":"推荐用途","inlineStyles":{"bold":[{"from":0,"to":4,"value":true}]}},{"textAlign":"center","verticalAlign":"middle","value":"其他用途","inlineStyles":{"bold":[{"from":0,"to":4,"value":true}]}},{"textAlign":"center","verticalAlign":"middle","value":"np.dot","inlineStyles":{"bold":[{"from":0,"to":6,"value":true}]}},{"textAlign":"center","verticalAlign":"middle","value":"向量点乘，结果为标量"},{"textAlign":"center","verticalAlign":"middle","value":"（矩阵乘法），（矩阵乘向量：把矩阵看成很多向量，分别和向量点乘，返回结果为数组）"},{"textAlign":"center","verticalAlign":"middle","value":"np.muliply","inlineStyles":{"bold":[{"from":0,"to":10,"value":true}]}},{"textAlign":"center","verticalAlign":"middle","value":"对应位置相乘"},{"textAlign":"center","verticalAlign":"middle","value":"（普通标量乘法)"},{"textAlign":"center","verticalAlign":"middle","value":"*","inlineStyles":{"bold":[{"from":0,"to":1,"value":true}]}},{"textAlign":"center","verticalAlign":"middle","value":"普通标量乘法"},{"textAlign":"center","verticalAlign":"middle","value":"(向量：对应位置相乘)，（方形矩阵：对应位置相乘）"}],"heights":[40,60,40,40],"widths":[206.66666666666666,206.66666666666666,206.66666666666666]}