意外的Python类型错误:使用标量时

我是Python的新手,我认为它与Java有很大不同。

我查看了其他答案,它们暗示错误的原因是我在期望传递一个值时却传递了一个数组。我不确定这一点。我相当肯定我只是在传递一个值。

第97行的代码是:exponential = math.exp(-(math.pow(feature_value-mean, 2) / (2*math.pow(standard_deviation, 2))))

错误的完整文本是:

Traceback (most recent call last):  File "D:/Personal/Python/NB.py", line 153, in <module>    main()  File "D:/Personal/Python/NB.py", line 148, in main    predictions = getPredict(summaries, testing_set)  File "D:/Personal/Python/NB.py", line 129, in getPredict    classification = predict(results, testData[index])  File "D:/Personal/Python/NB.py", line 117, in predict    probabilities = Classify(feature_summaries, classifications)  File "D:/Personal/Python/NB.py", line 113, in Classify    probabilities[classes] = probabilities[classes] * GaussianProbabilityDensity(feature_value, mean, standard_deviation)  File "D:/Personal/Python/NB.py", line 97, in GaussianProbabilityDensity    exponential = math.exp(-(math.pow(feature_value-mean, 2) / (2*math.pow(standard_deviation, 2))))TypeError: only size-1 arrays can be converted to Python scalars

如果有帮助,以下是csv文件的内容。值得注意的是,我有另外两个算法可以在这个数据集上正常运行。

| 0 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 || 0 | 1 | 1 | 1 | 1 | 1 | 1 | 0 | 0 | 0 | 0 || 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 || 0 | 1 | 1 | 1 | 0 | 0 | 1 | 0 | 1 | 0 | 0 || 0 | 0 | 0 | 0 | 1 | 0 | 0 | 0 | 0 | 0 | 0 || 0 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 0 | 1 || 0 | 0 | 0 | 0 | 0 | 0 | 1 | 0 | 0 | 0 | 0 || 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 || 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 0 || 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 || 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 || 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 || 0 | 1 | 0 | 0 | 1 | 0 | 0 | 1 | 1 | 0 | 1 || 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 || 0 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 || 0 | 1 | 1 | 1 | 1 | 1 | 0 | 1 | 1 | 0 | 1 || 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 || 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 || 0 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 0 | 1 | 1 || 0 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 || 0 | 1 | 0 | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 1 || 0 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 0 | 1 || 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 || 0 | 1 | 1 | 1 | 0 | 0 | 0 | 1 | 1 | 0 | 1 || 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 || 0 | 1 | 0 | 0 | 1 | 0 | 1 | 0 | 1 | 0 | 1 || 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 || 0 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 || 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 || 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 || 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 || 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 || 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 || 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 || 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 || 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 || 1 | 1 | 1 | 1 | 1 | 1 | 0 | 1 | 1 | 0 | 1 || 1 | 1 | 0 | 0 | 0 | 0 | 0 | 1 | 0 | 0 | 0 || 1 | 1 | 1 | 1 | 1 | 0 | 1 | 1 | 1 | 0 | 1 || 1 | 0 | 1 | 0 | 1 | 1 | 1 | 1 | 1 | 0 | 1 || 1 | 1 | 1 | 1 | 1 | 1 | 0 | 1 | 1 | 0 | 0 || 1 | 1 | 1 | 0 | 0 | 0 | 0 | 1 | 1 | 1 | 1 || 1 | 1 | 1 | 1 | 0 | 1 | 1 | 1 | 1 | 1 | 1 || 1 | 1 | 1 | 1 | 1 | 1 | 0 | 0 | 0 | 0 | 1 || 1 | 1 | 1 | 1 | 1 | 1 | 0 | 1 | 1 | 0 | 1 || 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 0 || 1 | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 0 | 1 || 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 || 1 | 0 | 0 | 0 | 1 | 0 | 0 | 0 | 0 | 0 | 0 |

回答:

math.pow(以及所有math函数)只能处理标量,即单个数字(整数或浮点数)。错误提示说其中一个参数,例如standard_deviation,是一个包含多个元素的numpy数组,因此无法转换为标量并传递给math.pow

这发生在你自己的代码中,因此追溯这些变量的来源并不困难。

要么是你无意中传递了一个数组给这个函数,要么你需要用np.pow(和np.exp)函数替换math.pow,这些函数可以处理数组。


你从csv文件加载数据时生成了一个numpy数组

data = numpy.loadtxt(data, delimiter=',')# 遍历数组中的数据for index in range(len(data)):    # 使用try catch尝试转换为浮点数,如果无法转换为浮点数,则转换为0    try:        data[index] = [float(x) for x in data[index]]    except ValueError:        data[index] = 0

loadtxt返回一个数组,默认类型是浮点数(dtype)。它的所有元素都将是浮点数——如果读取到不是有效浮点数的内容,它会引发错误。因此,不需要这个循环。而且这个循环看起来太像是为列表编写的,而不是为数组编写的。

randomize_data不应该返回任何内容。np.random.shuffle会就地操作csv。这不会引起错误。

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