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

源碼如下：

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()

錯誤如下：

---------------------------------------------------------------------------
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

錯誤原因：

傳遞的參數錯誤

train函數中第二個參數應該是數組的布局方式

應該根據傳入數組的形式填cv2.ml.ROW_SAMPLE或者cv2.ml.COL_SAMPLE

例如我的就是

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

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