Question

我正在尝试学习Python和Numpy，所以请耐心等待。我正在使用numpy.genfromtxt将CSV文件导入矩阵。 CSV如下所示：

Time(min),Nm,Speed,Power,Distance,Rpm,Bpm,interval,Altitude,Rate,Incline,Temp,PowerBalance,LeftTorqueEffectiveness,RightTorqueEffectiveness,getLeftPedalSmoothness,getRightPedalSmoothness,getCombinedPedalSmoothness,THb,SmO2,km
0.016666668,,4.3555064,0,0.002,0,118,1,684.3,0.0,0.0,14.71,50,-1.0,-1.0,-1.0,-1.0,-1.0,311.72,311.72
0.033333335,,4.3555064,20,0.002,0,119,1,684.3,0.0,0.0,14.71,50,-1.0,-1.0,-1.0,-1.0,-1.0,311.72,311.72
0.05,,4.444291,13,0.004,0,119,1,684.3,0.0,0.0,14.71,50,-1.0,-1.0,-1.0,-1.0,-1.0,311.72,311.72

现在我跑：

matrixCsv = np.genfromtxt(open(csvFile, "rb"), delimiter=',', \
                          missing_values=0,skip_header=1,dtype=float,\
                          usecols=(0,2,3,4,5,6,7,8,9,10,11,17),names=True)

我得到了：

[ (0.033333335, 4.3555064, 20.0, 0.002, 0.0, 119.0, 1.0, 684.3, 0.0, 0.0, 14.71, -1.0)
(0.05, 4.444291, 13.0, 0.004, 0.0, 119.0, 1.0, 684.3, 0.0, 0.0, 14.71, -1.0)
(0.06666667, 4.4781966, 16.0, 0.006, 0.0, 120.0, 1.0, 684.3, 0.0, 0.0, 14.71, -1.0)
...,

对我来说，看起来像元组封装成一个数组。但为什么元组呢？我知道numpy数组/矩阵需要是同构的，并且numpy会使非均匀数据产生元组。但为什么我的数据不均匀？我不明白......

Answer 1

您对如何使用skip_header和names感到困惑。读取数据并将第一行用作变量名的正确方法是：

In [185]:

np.genfromtxt('temp.csv', delimiter=',', \
                          missing_values=0,skip_header=0,dtype=float,\
                          usecols=(0,2,3,4,5,6,7,8,9,10,11,17),names=True)
Out[185]:
array([ (0.016666668, 4.3555064, 0.0, 0.002, 0.0, 118.0, 1.0, 684.3, 0.0, 0.0, 14.71, -1.0),
       (0.033333335, 4.3555064, 20.0, 0.002, 0.0, 119.0, 1.0, 684.3, 0.0, 0.0, 14.71, -1.0),
       (0.05, 4.444291, 13.0, 0.004, 0.0, 119.0, 1.0, 684.3, 0.0, 0.0, 14.71, -1.0)], 
      dtype=[('Timemin', '<f8'), ('Speed', '<f8'), ('Power', '<f8'), ('Distance', '<f8'), ('Rpm', '<f8'), ('Bpm', '<f8'), ('interval', '<f8'), ('Altitude', '<f8'), ('Rate', '<f8'), ('Incline', '<f8'), ('Temp', '<f8'), ('getCombinedPedalSmoothness', '<f8')])

它不是tuple的数组，而是structured array。 skip_header=1将使用第一行数据作为名称，这可能不是您想要的（请参阅如何丢失第一行数据？）。

您还可以删除名称并将数据读入普通numpy array。

In [186]:

np.genfromtxt('temp.csv', delimiter=',', \
                          missing_values=0,skip_header=1,dtype=float,\
                          usecols=(0,2,3,4,5,6,7,8,9,10,11,17))
Out[186]:
array([[  1.66666680e-02,   4.35550640e+00,   0.00000000e+00,
          2.00000000e-03,   0.00000000e+00,   1.18000000e+02,
          1.00000000e+00,   6.84300000e+02,   0.00000000e+00,
          0.00000000e+00,   1.47100000e+01,  -1.00000000e+00],
       [  3.33333350e-02,   4.35550640e+00,   2.00000000e+01,
          2.00000000e-03,   0.00000000e+00,   1.19000000e+02,
          1.00000000e+00,   6.84300000e+02,   0.00000000e+00,
          0.00000000e+00,   1.47100000e+01,  -1.00000000e+00],
       [  5.00000000e-02,   4.44429100e+00,   1.30000000e+01,
          4.00000000e-03,   0.00000000e+00,   1.19000000e+02,
          1.00000000e+00,   6.84300000e+02,   0.00000000e+00,
          0.00000000e+00,   1.47100000e+01,  -1.00000000e+00]])

numpy.genfromtxt导入元组而不是数组

1 个答案: