title: what is the purpose of FLATTEN operator in PIG Latin
body: <p>A = load 'data' as (x, y);</p>
  
  <p>B = load 'data' as (x, z);</p>
  
  <p>C = cogroup A by x, B by x;</p>
  
  <p>D = foreach C generate flatten(A), flatten(b);</p>
  
  <p>E = group D by A::x</p>
  
  <p>what exactly done in the above statements and where we use flatten in realtime scenario.</p>