numpy之多维数组的创建全过程

numpy多维数组的创建

多维数组（矩阵ndarray）

ndarray的基本属性

• shape维度的大小

• ndim维度的个数

• dtype数据类型

1.1 随机抽样创建

1.1.1 rand

生成指定维度的随机多维度浮点型数组，区间范围是[0,1)

Random values in a given shape.
           Create an array of the given shape and populate it with
           random samples from a uniform distribution
           over ``[0, 1)``.
nd1 = np.random.rand(1,1)
print(nd1)
print('维度的个数',nd1.ndim)
print('维度的大小',nd1.shape)
print('数据类型',nd1.dtype)   # float 64

1.1.2 uniform

def uniform(low=0.0, high=1.0, size=None): # real signature unknown; restored from __doc__
   """
   uniform(low=0.0, high=1.0, size=None)
           Draw samples from a uniform distribution.
           Samples are uniformly distributed over the half-open interval
           ``[low, high)`` (includes low, but excludes high).  In other words,
           any value within the given interval is equally likely to be drawn
           by `uniform`.
           Parameters
           ----------
           low : float or array_like of floats, optional
               Lower boundary of the output interval.  All values generated will be
               greater than or equal to low.  The default value is 0.
           high : float or array_like of floats
               Upper boundary of the output interval.  All values generated will be
               less than high.  The default value is 1.0.
           size : int or tuple of ints, optional
               Output shape.  If the given shape is, e.g., ``(m, n, k)``, then
               ``m * n * k`` samples are drawn.  If size is ``None`` (default),
               a single value is returned if ``low`` and ``high`` are both scalars.
               Otherwise, ``np.broadcast(low, high).size`` samples are drawn.
           Returns
           -------
           out : ndarray or scalar
               Drawn samples from the parameterized uniform distribution.
           See Also
           --------
           randint : Discrete uniform distribution, yielding integers.
           random_integers : Discrete uniform distribution over the closed
                             interval ``[low, high]``.
           random_sample : Floats uniformly distributed over ``[0, 1)``.
           random : Alias for `random_sample`.
           rand : Convenience function that accepts dimensions as input, e.g.,
                  ``rand(2,2)`` would generate a 2-by-2 array of floats,
                  uniformly distributed over ``[0, 1)``.
           Notes
           -----
           The probability density function of the uniform distribution is
           .. math:: p(x) = \frac{1}{b - a}
           anywhere within the interval ``[a, b)``, and zero elsewhere.
           When ``high`` == ``low``, values of ``low`` will be returned.
           If ``high`` < ``low``, the results are officially undefined
           and may eventually raise an error, i.e. do not rely on this
           function to behave when passed arguments satisfying that
           inequality condition.
           Examples
           --------
           Draw samples from the distribution:
           >>> s = np.random.uniform(-1,0,1000)
           All values are within the given interval:
           >>> np.all(s >= -1)
           True
           >>> np.all(s < 0)
           True
           Display the histogram of the samples, along with the
           probability density function:
           >>> import matplotlib.pyplot as plt
           >>> count, bins, ignored = plt.hist(s, 15, density=True)
           >>> plt.plot(bins, np.ones_like(bins), linewidth=2, color='r')
           >>> plt.show()
   """
   pass

nd2 = np.random.uniform(-1,5,size = (2,3))
print(nd2)
print('维度的个数',nd2.ndim)
print('维度的大小',nd2.shape)
print('数据类型',nd2.dtype)

运行结果：

1.1.3 randint

def randint(low, high=None, size=None, dtype='l'): # real signature unknown; restored from __doc__
   """
   randint(low, high=None, size=None, dtype='l')
           Return random integers from `low` (inclusive) to `high` (exclusive).
           Return random integers from the "discrete uniform" distribution of
           the specified dtype in the "half-open" interval [`low`, `high`). If
           `high` is None (the default), then results are from [0, `low`).
           Parameters
           ----------
           low : int
               Lowest (signed) integer to be drawn from the distribution (unless
               ``high=None``, in which case this parameter is one above the
               *highest* such integer).
           high : int, optional
               If provided, one above the largest (signed) integer to be drawn
               from the distribution (see above for behavior if ``high=None``).
           size : int or tuple of ints, optional
               Output shape.  If the given shape is, e.g., ``(m, n, k)``, then
               ``m * n * k`` samples are drawn.  Default is None, in which case a
               single value is returned.
           dtype : dtype, optional
               Desired dtype of the result. All dtypes are determined by their
               name, i.e., 'int64', 'int', etc, so byteorder is not available
               and a specific precision may have different C types depending
               on the platform. The default value is 'np.int'.
               .. versionadded:: 1.11.0
           Returns
           -------
           out : int or ndarray of ints
               `size`-shaped array of random integers from the appropriate
               distribution, or a single such random int if `size` not provided.
           See Also
           --------
           random.random_integers : similar to `randint`, only for the closed
               interval [`low`, `high`], and 1 is the lowest value if `high` is
               omitted. In particular, this other one is the one to use to generate
               uniformly distributed discrete non-integers.
           Examples
           --------
           >>> np.random.randint(2, size=10)
           array([1, 0, 0, 0, 1, 1, 0, 0, 1, 0])
           >>> np.random.randint(1, size=10)
           array([0, 0, 0, 0, 0, 0, 0, 0, 0, 0])
           Generate a 2 x 4 array of ints between 0 and 4, inclusive:
           >>> np.random.randint(5, size=(2, 4))
           array([[4, 0, 2, 1],
                  [3, 2, 2, 0]])
   """
   pass

nd3 = np.random.randint(1,20,size=(3,4))
print(nd3)
print('维度的个数',nd3.ndim)
print('维度的大小',nd3.shape)
print('数据类型',nd3.dtype)
展示：
[[11 17  5  6]
[17  1 12  2]
[13  9 10 16]]
维度的个数 2
维度的大小 (3, 4)
数据类型 int32

注意点：

1、如果没有指定最大值，只是指定了最小值，范围是[0,最小值）

2、如果有最小值，也有最大值，范围为[最小值,最大值)

1.2 序列创建

1.2.1 array

通过列表进行创建
nd4 = np.array([1,2,3])
展示：
[1 2 3]
通过列表嵌套列表创建
nd5 = np.array([[1,2,3],[4,5]])
展示：
[list([1, 2, 3]) list([4, 5])]
综合
nd4 = np.array([1,2,3])
print(nd4)
print(nd4.ndim)
print(nd4.shape)
print(nd4.dtype)
nd5 = np.array([[1,2,3],[4,5,6]])
print(nd5)
print(nd5.ndim)
print(nd5.shape)
print(nd5.dtype)
展示：
[1 2 3]
1
(3,)
int32
[[1 2 3]
[4 5 6]]
2
(2, 3)
int32

1.2.2 zeros

nd6 = np.zeros((4,4))
print(nd6)
展示：
[[0. 0. 0. 0.]
[0. 0. 0. 0.]
[0. 0. 0. 0.]
[0. 0. 0. 0.]]
注意点：
1、创建的数里面的数据为0
2、默认的数据类型是float
3、可以指定其他的数据类型

1.2.3 ones

nd7 = np.ones((4,4))
print(nd7)
展示：
[[1. 1. 1. 1.]
[1. 1. 1. 1.]
[1. 1. 1. 1.]
[1. 1. 1. 1.]]

1.2.4 arange

nd8 = np.arange(10)
print(nd8)
nd9 = np.arange(1,10)
print(nd9)
nd10 = np.arange(1,10,2)
print(nd10)

结果：

[0 1 2 3 4 5 6 7 8 9]
[1 2 3 4 5 6 7 8 9]
[1 3 5 7 9]

注意点：

• 1、只填写一位数，范围：[0,填写的数字)

• 2、填写两位，范围：[最低位，最高位)

• 3、填写三位，填写的是（最低位，最高位，步长）

• 4、创建的是一位数组

• 5、等同于np.array(range())

1.3 数组重新排列

nd11 = np.arange(10)
print(nd11)
nd12 = nd11.reshape(2,5)
print(nd12)
print(nd11)
展示：
[0 1 2 3 4 5 6 7 8 9]
[[0 1 2 3 4]
[5 6 7 8 9]]
[0 1 2 3 4 5 6 7 8 9]
注意点：
1、有返回值，返回新的数组，原始数组不受影响
2、进行维度大小的设置过程中，要注意数据的个数，注意元素的个数
nd13 = np.arange(10)
print(nd13)
nd14 = np.random.shuffle(nd13)
print(nd14)
print(nd13)
展示：
[0 1 2 3 4 5 6 7 8 9]
None
[8 2 6 7 9 3 5 1 0 4]
注意点：
1、在原始数据集上做的操作
2、将原始数组的元素进行重新排列，打乱顺序
3、shuffle这个是没有返回值的

两个可以配合使用，先打乱，在重新排列

1.4 数据类型的转换

nd15 = np.arange(10,dtype=np.int64)
print(nd15)
nd16 = nd15.astype(np.float64)
print(nd16)
print(nd15)
展示：
[0 1 2 3 4 5 6 7 8 9]
[0. 1. 2. 3. 4. 5. 6. 7. 8. 9.]
[0 1 2 3 4 5 6 7 8 9]
注意点：
1、astype()不在原始数组做操作，有返回值，返回的是更改数据类型的新数组
2、在创建新数组的过程中，有dtype参数进行指定

1.5 数组转列表

arr1 = np.arange(10)
# 数组转列表
print(list(arr1))
print(arr1.tolist())
展示：
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

numpy 多维数组相关问题

创建（多维）数组

x = np.zeros(shape=[10, 1000, 1000], dtype='int')

得到全零的多维数组。

数组赋值

x[*,*,*] = ***

np数组保存

np.save("./**.npy",x)

读取np数组

x = np.load("path")

来源：https://blog.csdn.net/Sahar_/article/details/99469328