numpy库中的一些函数简介、使用方法

1、np.concatenate()

1.1、函数案例


import numpy as np

a=np.array([1,2,3])
b=np.array([11,22,33])
c=np.array([44,55,66])
d=np.concatenate((a,b,c),axis=0)  # 默认情况下，axis=0可以不写
print(d)  #输出array([ 1,  2,  3, 11, 22, 33, 44, 55, 66])，对于一维数组拼接，axis的值不影响最后的结果

1.2、函数用法

concatenate Found at: numpy.core.multiarray
concatenate((a1, a2, ...), axis=0, out=None)
Join a sequence of arrays along an existing axis.
Parameters
----------
a1, a2, ... : sequence of array_like. The arrays must have the same shape, except in the dimension  corresponding to `axis` (the first, by default).
axis : int, optional. The axis along which the arrays will be joined. Default is 0.
out : ndarray, optional. If provided, the destination to place the result. The shape must be correct, matching that of what concatenate would have   returned if no  out argument were specified.

Returns
-------
res : ndarray
The concatenated array.

在:numpy.core.multiarray找到连接
连接((a1, a2，…)，axis=0, out=None)
沿着现有的轴连接数组序列。
参数
----------
a1, a2,…:数组类型的序列。数组必须具有相同的形状，除了与“axis”对应的维度(默认情况下为第一个维度)。
axis: int，可选。数组连接的轴线。默认值为0。
out : ndarray，可选。如果提供，放置结果的目的地。形状必须正确，如果没有指定out参数，则匹配concatenate将返回的形状。

返回
-------
res: ndarray
连接后的字符串数组。

See Also
--------
ma.concatenate : Concatenate function that preserves input   masks.
array_split : Split an array into multiple sub-arrays of equal or
near-equal size.
split : Split array into a list of multiple sub-arrays of equal size.
hsplit : Split array into multiple sub-arrays horizontally   (column wise)
vsplit : Split array into multiple sub-arrays vertically (row wise)
dsplit : Split array into multiple sub-arrays along the 3rd axis (depth).
stack : Stack a sequence of arrays along a new axis.
hstack : Stack arrays in sequence horizontally (column wise)
vstack : Stack arrays in sequence vertically (row wise)
dstack : Stack arrays in sequence depth wise (along third dimension)

Notes
-----
When one or more of the arrays to be concatenated is a MaskedArray,   this function will return a MaskedArray object instead of an ndarray, but the input masks are *not* preserved. In cases where a   MaskedArray  is expected as input, use the ma.concatenate function from the masked  array module instead.

另请参阅
--------
马。保存输入掩码的连接函数。
array_split:将一个数组分割成多个相等或的子数组
与大小。
分割:将数组分割成相同大小的多个子数组。
hsplit:水平(按列)将数组分割为多个子数组
垂直(按行)将数组分割为多个子数组
dsplit:沿着第三轴(深度)将数组分割成多个子数组。
堆栈:将数组序列沿着一个新的轴进行堆栈。
hstack:水平排列(按列排列)
垂直(行向)按顺序堆叠数组。
dstack:按深度顺序排列的堆栈数组(沿三维方向)
笔记
-----
当一个或多个要连接的数组是一个MaskedArray时，这个函数将返回一个MaskedArray对象而不是ndarray，但是输入掩码*不*保留。在需要MaskedArray作为输入的情况下，使用ma。连接函数从掩码数组模块代替。

Examples
--------
>>> a = np.array([[1, 2], [3, 4]])
>>> b = np.array([[5, 6]])
>>> np.concatenate((a, b), axis=0)
array([[1, 2],
[3, 4],
[5, 6]])
>>> np.concatenate((a, b.T), axis=1)
array([[1, 2, 5],
[3, 4, 6]])

This function will not preserve masking of MaskedArray
inputs.

>>> a = np.ma.arange(3)
>>> a[1] = np.ma.masked
>>> b = np.arange(2, 5)
>>> a
masked_array(data = [0 -- 2],
mask = [False True False],
fill_value = 999999)
>>> b
array([2, 3, 4])
>>> np.concatenate([a, b])
masked_array(data = [0 1 2 2 3 4],
mask = False,
fill_value = 999999)
>>> np.ma.concatenate([a, b])
masked_array(data = [0 -- 2 2 3 4],
mask = [False True False False False False],
fill_value = 999999)

2、np.meshgrid()

2.1、函数案例

X, Y = np.meshgrid(X, Y)

2.2、函数用法

meshgrid Found at: numpy.lib.function_base
Return coordinate matrices from coordinate vectors.

Make N-D coordinate arrays for vectorized evaluations of N-D scalar/vector fields over N-D grids, given  one-dimensional coordinate arrays x1, x2,..., xn.

.. versionchanged:: 1.9
1-D and 0-D cases are allowed.

Parameters
----------
x1, x2,..., xn : array_like
1-D arrays representing the coordinates of a grid.
indexing : {'xy', 'ij'}, optional
Cartesian ('xy', default) or matrix ('ij') indexing of output.
See Notes for more details.

.. versionadded:: 1.7.0
sparse : bool, optional
If True a sparse grid is returned in order to conserve memory. Default is False.

.. versionadded:: 1.7.0
copy : bool, optional. If False, a view into the original arrays are returned in
order to  conserve memory. Default is True. Please note that  ``sparse=False, copy=False`` will likely return noncontiguous arrays. Furthermore, more than one element of a   broadcast array may refer to a single memory location. If you need to  write to the arrays, make copies first.

.. versionadded:: 1.7.0

Returns
-------
X1, X2,..., XN : ndarray
For vectors `x1`, `x2`,..., 'xn' with lengths ``Ni=len(xi)`` ,
return ``(N1, N2, N3,...Nn)`` shaped arrays if indexing='ij'   or ``(N2, N1, N3,...Nn)`` shaped arrays if indexing='xy'  with the elements of `xi` repeated to fill the matrix along  the first dimension for `x1`, the second for `x2` and so on.

Notes
-----
This function supports both indexing conventions through the indexing keyword argument. Giving the string 'ij' returns a  meshgrid with matrix indexing, while 'xy' returns a meshgrid with   Cartesian indexing.
In the 2-D case with inputs of length M and N, the outputs are of shape  (N, M) for 'xy' indexing and (M, N) for 'ij' indexing. In the   3-D case with inputs of length M, N and P, outputs are of shape   (N, M, P) for   'xy' indexing and (M, N, P) for 'ij' indexing. The difference is  illustrated by the following code snippet::

xv, yv = np.meshgrid(x, y, sparse=False, indexing='ij')
for i in range(nx):
for j in range(ny):
# treat xv[i,j], yv[i,j]

xv, yv = np.meshgrid(x, y, sparse=False, indexing='xy')
for i in range(nx):
for j in range(ny):
# treat xv[j,i], yv[j,i]

In the 1-D and 0-D case, the indexing and sparse keywords have no effect.

See Also
--------
index_tricks.mgrid : Construct a multi-dimensional    "meshgrid" using indexing notation.
index_tricks.ogrid : Construct an open multi-dimensional   "meshgrid" using indexing notation.

从坐标向量返回坐标矩阵。

建立N-D坐标阵列，在N-D网格上对N-D标量/向量场进行向量化计算，给定一维坐标阵列x1, x2，…,xn。

. .versionchanged:: 1.9
允许1-D和0-D。

参数
----------
x1, x2,…， xn: array_like
表示网格坐标的一维数组。
索引:{'xy'， 'ij'}，可选
Cartesian ('xy'，默认)或矩阵('ij')索引的输出。
参见注释了解更多细节。

. .versionadded: 1.7.0
稀疏:bool，可选
如果为真，则返回一个稀疏网格以保存内存。默认是假的。

. .versionadded: 1.7.0
复制:bool，可选。如果为假，则返回原始数组的视图
为了保存记忆。默认是正确的。请注意，' ' sparse=False, copy=False ' '将可能返回不相邻的数组。此外，广播数组中的多个元素可以引用单个内存位置。如果需要对数组进行写入，请首先进行复制。

. .versionadded: 1.7.0

返回
-------
X1, X2,…XN: ndarray
对于向量“x1”，“x2”，…， 'xn'加上length ' ' ' Ni=len(xi) ' '，
返回' ' (N1, N2, N3，…Nn) ' '形数组如果索引='ij'或' ' (N2, N1, N3，…Nn) ' '形数组如果索引='xy'与元素' xi '重复填充矩阵沿第一个维度为' x1 '，第二个为' x2 '，以此类推。

笔记
-----
这个函数通过索引关键字参数支持两种索引约定。给出字符串'ij'返回一个带矩阵索引的meshgrid，而'xy'返回一个带笛卡尔索引的meshgrid。
在输入长度为M和N的二维情况下，输出的形状为(N, M)，表示“xy”索引，(M, N)表示“ij”索引。在输入长度为M、N和P的3-D情况下，输出的形状(N、M、P)表示“xy”索引，(M、N、P)表示“ij”索引。区别如下面的代码片段所示::

xv yv = np。meshgrid(x, y, sparse=False, index ='ij')
i在range(nx)内:
j in range(ny):
治疗xv[i,j]， yv[i,j]

xv yv = np。meshgrid(x, y, sparse=False, index ='xy')
i在range(nx)内:
j in range(ny):

在1-D和0-D情况下，索引和稀疏关键字没有影响。。

另请参阅
--------
index_tricks。mgrid:使用索引符号构造一个多维“meshgrid”。
index_tricks。ogrid:使用索引符号构造一个开放的多维“meshgrid”。

Examples
--------
>>> nx, ny = (3, 2)
>>> x = np.linspace(0, 1, nx)
>>> y = np.linspace(0, 1, ny)
>>> xv, yv = np.meshgrid(x, y)
>>> xv
array([[ 0. , 0.5, 1. ],
[ 0. , 0.5, 1. ]])
>>> yv
array([[ 0., 0., 0.],
[ 1., 1., 1.]])
>>> xv, yv = np.meshgrid(x, y, sparse=True) # make
sparse output arrays
>>> xv
array([[ 0. , 0.5, 1. ]])
>>> yv
array([[ 0.],
[ 1.]])

`meshgrid` is very useful to evaluate functions on a grid.

>>> x = np.arange(-5, 5, 0.1)
>>> y = np.arange(-5, 5, 0.1)
>>> xx, yy = np.meshgrid(x, y, sparse=True)
>>> z = np.sin(xx**2 + yy**2) / (xx**2 + yy**2)
>>> h = plt.contourf(x,y,z)

Py之numpy：numpy库的使用方法之基础函数(np.concatenate/np.meshgrid等)简介、使用方法之详细攻略