title: The reading of files throughout Numpy library
body: <p>I'm trying to read data in a <code>text file</code> by using <code>Numpy</code> and these data as shown below:</p>
  
  <pre><code># Student data collected on 17 July 2014
  # Researcher: Dr Wicks, University College Newbury
  
  # The following data relate to N = 20 students. It
  # has been totally made up and so therefore is 100%
  # anonymous.
  
  Subject  Sex    DOB     Height  Weight   BP     VO2max
  (ID)     M/F dd/mm/yy     m       kg    mmHg   mL.kg-1.min-1
  JW-1     M   19/12/95    1.82    92.4  119/76    39.3
  JW-2     M   11/1/96     1.77    80.9  114/73    35.5
  JW-3     F    2/10/95    1.68    69.7  124/79    29.1
  JW-6     M    6/7/95     1.72    75.5  110/60    45.5
  # JW-7   F   28/3/96     1.66    72.4  101/68      -
  JW-9     F   11/12/95    1.78    82.1  115/75    32.3
  JW-10    F   7/4/96      1.60      -    -/-      30.1
  JW-11    M   22/8/95     1.72    77.2  97/63     48.8
  JW-12    M   23/5/96     1.83    88.9  105/70    37.7
  JW-14    F   12/1/96     1.56    56.3  108/72    26.0
  JW-15    F   1/6/96      1.64    65.0  99/67     35.7
  JW-16    M   10/9/95     1.63    73.0  131/84    29.9
  JW-17    M   17/2/96     1.67    89.8  101/76    40.2
  JW-18    M   31/7/96     1.66    75.1   -/-        -
  JW-19    F   30/10/95    1.59    67.3  103/69    33.5
  JW-22    F   9/3/96      1.70     -    119/80    30.9
  JW-23    M   15/5/95     1.97    89.2  124/82      -
  JW-24    F   1/12/95     1.66    63.8  100/78      -
  JW-25    F   25/10/95    1.63    64.4   -/-      28.0
  JW-26    M   17/4/96     1.69      -   121/82    39.
  </code></pre>
  
  <p>I read the <code>sex</code> and <code>Height columns</code> and I faced no problem throughout my below code:</p>
  
  <pre><code>import numpy as np
  
  fname = 'D:\\NumpyTutorial.txt'
  datatype1 = np.dtype([('sex','|S1'),('height','f8')])
  a = np.loadtxt(fname, dtype=datatype1, skiprows=9, usecols=(1,3))
  print(a)
  </code></pre>
  
  <p>But when I tried to read the <code>Weight column</code> with this code below:</p>
  
  <pre><code>import numpy as np
  
  fname = 'D:\\NumpyTutorial.txt'
  datatype1 = np.dtype([('sex','|S1'),('height','f8'),('Weight','f8')])
  a = np.loadtxt(fname, dtype=datatype1, skiprows=9, usecols=(1,3,4))
  print(a)
  </code></pre>
  
  <p>I got this error:</p>
  
  <pre><code>ValueError: could not convert string to float: '-'.
  </code></pre>
  
  <p>1- How could I deal with this <code>sign(-)</code>.How can I read this column?. </p>
  
  <p>2- For <code>sex column</code> I used <code>'|S1'</code> and for <code>height</code> used <code>'f8'</code>, what is the <code>syntax</code> for <code>Subject, BOD and BP columns</code> until to read them?.</p>
  
  <p>3 - How could I display everything in this file?</p>