only size-1 arrays can be converted to Python scalars

python版本：3.6.5

opencv版本：3.2.0

使用的jupyter notebook

源码如下：

import cv2
import numpy as np
import matplotlib.pyplot as plt

%matplotlib inline

# Feature set containing (x,y) values of 25 known/training data
trainData = np.random.randint(0,100,(25,2)).astype(np.float32)

# Labels each one either Red or Blue with numbers 0 and 1
responses = np.random.randint(0,2,(25,1)).astype(np.float32)

# Take Red families and plot them
red = trainData[responses.ravel()==0]
plt.scatter(red[:,0],red[:,1],80,'r','^')

# Take Blue families and plot them
blue = trainData[responses.ravel()==1]
plt.scatter(blue[:,0],blue[:,1],80,'b','s')

# plt.show()

newcomer = np.random.randint(0,100,(1,2)).astype(np.float32)
plt.scatter(newcomer[:,0],newcomer[:,1],80,'g','o')

knn = cv2.ml.KNearest_create()

knn.train(trainData,responses)
ret, results, neighbours ,dist = knn.findNearest(newcomer, 3)

print ("result: ", results,"\n")
print ("neighbours: ", neighbours,"\n")
print ("distance: ", dist)

plt.show()

错误如下：

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-21-b1c5cdca5e57> in <module>()
     20 knn = cv2.ml.KNearest_create()
     21
---> 22 knn.train(trainData,responses)
     23 ret, results, neighbours ,dist = knn.findNearest(newcomer, 3)
     24 

TypeError: only size-1 arrays can be converted to Python scalars

错误原因：

传递的参数错误

train函数中第二个参数应该是数组的布局方式

应该根据传入数组的形式填cv2.ml.ROW_SAMPLE或者cv2.ml.COL_SAMPLE

例如我的就是

knn.train(trainData,cv2.ml.ROW_SAMPLE，responses)

参考地址：https://stackoverflow.com/questions/33975695/type-error-only-length-1-arrays-can-be-converted-to-python-scalars