numpy.squeeze()

numpy.squeeze()

在吴恩达深度学习视频的作业里，经常遇到这样的情况。

ValueError: c of shape (1, 300) not acceptable as a color sequence for x with size 300, y with size 300

这是因为matplotlib.pyplot接收的color sequence 参数c应该是单个值，直接传Y或者Y.train传的是shape(1, size)的矩阵。

解决方案：

import numpy as np

np.squeeze(Y)
np.squeeze(Y.train)

np.squeeze这个函数的作用是去掉矩阵里维度为1的维度。

例：(1, 300)的矩阵经由np.squeeze处理后变成300; (200, 1, 300)的矩阵经由np.squeeze处理后变成(200, 300)。

详情请参阅官方文档：

numpy.squeeze
numpy.squeeze(a, axis=None)[source]
Remove single-dimensional entries from the shape of an array.

Parameters:	
a : array_like

Input data.

axis : None or int or tuple of ints, optional

New in version 1.7.0.

Selects a subset of the single-dimensional entries in the shape. If an axis is selected with shape entry greater than one, an error is raised.

Returns:	
squeezed : ndarray

The input array, but with all or a subset of the dimensions of length 1 removed. This is always a itself or a view into a.

Examples

>>>
>>> x = np.array([[[0], [1], [2]]])
>>> x.shape
(1, 3, 1)
>>> np.squeeze(x).shape
(3,)
>>> np.squeeze(x, axis=(2,)).shape
(1, 3)