title: Extract specific observations of csv file in R
body: <p>I've imported a csv file using read.csv.
  It gives me a data frame with 18k observations of 1 variable, which looks like this:</p>
  
  <pre><code>    V1
  1   Energies (kJ/mol)
  2              Bond          Angle    Proper Dih.  Improper Dih.          LJ-14
  3       3.12912e+04    4.12307e+03    1.63677e+04    1.25619e+02    1.04394e+04
  4        Coulomb-14        LJ (SR)   Coulomb (SR)      Potential Pressure (bar)
  5       9.21339e+04    2.82339e+05   -1.15807e+06   -7.21252e+05   -7.25781e+03
  6              Step           Time         Lambda
  7                 1        1.00000        0.00000
  8      Energies (kJ/mol)
  9              Bond          Angle    Proper Dih.  Improper Dih.          LJ-14
  10      2.71553e+04    4.11858e+03    1.63855e+04    1.22226e+02    1.03903e+04
  11       Coulomb-14        LJ (SR)   Coulomb (SR)      Potential Pressure (bar)
  12      9.20926e+04    2.65253e+05   -1.15928e+06   -7.43766e+05   -7.27887e+03
  13             Step           Time         Lambda
  14                2        2.00000        0.00000
  
  ...
  </code></pre>
  
  <p>I want to extract the Potential energy in a vector. I've tried grep and readLines in multiple varieties and functions, but nothing works. Does anybody have an idea how to solve this problem?
  Thanks! :)</p>