Python3--我的代码库之Axis（五）

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一、Along an Axis

Axes are defined for arrays with more than one dimension.

A 2-dimensional array has two corresponding axes:

The first running vertically downwards across rows (axis 0)
The second running horizontally across columns (axis 1)

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解释

1. 轴这个概念是为不止一个维度的数组准备的；
2. axis = 0,第一个维度，垂直向下贯穿所有行数据，数据聚合时，注意贯穿，合并数组时，注意垂直向下；
3. axis = 1,第二个维度，水平贯穿所有列数据，注意的点如上；

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For example

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a = array([[1, 2, 3],
                  [4, 5, 6]])
b = array([[2, 3, 4],
                  [5, 6, 7]])

np.sum((a),axis=0) # 向下贯穿所有行数据，即按照分别计算所有列的和

Out:

array([5, 7, 9])

np.sum((b),axis=1) # 水平贯穿所有列数据，即按照分别计算所有行的和

Out:

array([ 9, 18])

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二、Merge’s Axis

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a = array([[1, 2, 3],
                  [4, 5, 6]])
b = array([[2, 3, 4],
                  [5, 6, 7]])
np.concatenate((a,b),axis = 0) #vertically downwards,垂直向下合并

Out:

array([[1, 2, 3],
          [4, 5, 6],
          [2, 3, 4],
          [5, 6, 7]])

np.concatenate((a,b),axis = 1) #horizontally,水平合并
Out[37]:
array([[1, 2, 3, 2, 3, 4],
[4, 5, 6, 5, 6, 7]])

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