title: Numpy cumulative sum for csv rows gives type error
body: <p>I'm using cumsum function to calculate cumulative sum of a csv column(rows). Input looks like this:</p>
  
  <p>input (average_):</p>
  
  <pre><code>1   0.000053    0.004531    0.010447    0.051962
  2   0.000589    0.004518    0.009801    0.052226
  3   0.000083    0.004581    0.010362    0.052288
  4   -0.000192   0.003726    0.011258    0.051094
  5   0.000281    0.004078    0.01008     0.052156
  6   0.000091    0.004028    0.009853    0.052301
  7   0.000478    0.004298    0.009966    0.054803
  8   0.00028     0.004267    0.010051    0.050296
  9   0.000198    0.004766    0.010245    0.051754
  </code></pre>
  
  <p>but this code:</p>
  
  <pre><code>acc_column = []
  for row in average_:
      f_column = numpy.cumsum(row[1], dtype = float)
      acc_column.append(f_column)
  </code></pre>
  
  <p>doesn't work and gives the error:</p>
  
  <pre><code>"TypeError: cannot perform accumulate with flexible type"
  </code></pre>
  
  <p>Any ideas what am I doing wrong please?</p>