title: mapper function is always needed in a mapreduce program?
body: <p>Im trying to develop a hadoop mapreduce program to calculate the maximum temperature inside a text file.</p>
  
  <p>The input text file looks like this:</p>
  
  <p>City1 - 10 </p>
  
  <p>City2 - 15</p>
  
  <p>City3 - 4</p>
  
  <p>city4 - 20</p>
  
  <p>Im beginner in mapreduce, but I read that with mapper, the output should be the input transformed in meaningful key value pairs. But If I already have a input file like below, I dont need to write a mapper file (because is already with key value pairs)??</p>
  
  <p>City1 10</p>
  
  <p>City2 15</p>
  
  <p>City3 4</p>
  
  <p>city 4 10</p>
  
  <p>I was trying to develop the mapper file but Im not understanding if its really necessary in this case.</p>
  
  <p>Code:</p>
  
  <pre><code>for line in sys.stdin:
  
      line = line.strip()
      print line
  </code></pre>