在Python中使用numpy.sum()

Python的numpy.sum()函数用于沿给定轴获取数组元素的和。

Python的numpy库中sum()函数的语法。

Python NumPy sum()方法的语法是：

sum(array, axis, dtype, out, keepdims, initial)

• The array elements are used to calculate the sum.
• If the axis is not provided, the sum of all the elements is returned. If the axis is a tuple of ints, the sum of all the elements in the given axes is returned.
• We can specify dtype to specify the returned output data type.
• The out variable is used to specify the array to place the result. It’s an optional parameter.
• The keepdims is a boolean parameter. If this is set to True, the axes which are reduced are left in the result as dimensions with size one.
• The initial parameter specifies the starting value for the sum.

Python numpy sum() 示例

让我们来看一些numpy.sum()函数的示例。

数组中所有元素的总和

如果我们只通过数组将其传递给 sum() 函数，它将被扁平化，并返回所有元素的总和。

import numpy as np

array1 = np.array(
    [[1, 2],
     [3, 4],
     [5, 6]])

total = np.sum(array1)
print(f'Sum of all the elements is {total}')

输出：所有元素的和为21。

2. 沿轴的数组元素之和

如果我们指定了轴值，将返回沿该轴的元素之和。如果数组形状为（X，Y），则沿0轴的求和结果形状将为（1，Y）。沿1轴的求和结果形状将为（1，X）。

import numpy as np

array1 = np.array(
    [[1, 2],
     [3, 4],
     [5, 6]])

total_0_axis = np.sum(array1, axis=0)
print(f'Sum of elements at 0-axis is {total_0_axis}')

total_1_axis = np.sum(array1, axis=1)
print(f'Sum of elements at 1-axis is {total_1_axis}')

输出：

Sum of elements at 0-axis is [ 9 12]
Sum of elements at 1-axis is [ 3  7 11]

3. 指定求和的输出数据类型

import numpy as np

array1 = np.array(
    [[1, 2],
     [3, 4]])

total_1_axis = np.sum(array1, axis=1, dtype=float)
print(f'Sum of elements at 1-axis is {total_1_axis}')

输出：一维轴上元素之和为[3. 7.]

4. 总和的初始值

import numpy as np

array1 = np.array(
    [[1, 2],
     [3, 4]])

total_1_axis = np.sum(array1, axis=1, initial=10)
print(f'Sum of elements at 1-axis is {total_1_axis}')

输出：1轴上元素的总和为[13 17] 参考：API文档