title: Subset one dataframe from a second
body: <p>I am sure I am missing a simple solution but I have been unable to figure this out, and have yet to find the answer in the existing questions. (If it is not obvious, I am a hack and just learning Python)</p>
  
  <p>Lets say I have two data frames (DataFileDF, SelectedCellsRaw) with the same two key fields (MRBTS, LNCEL) and I want a subset of the first data frame (DataFileDF) containing only the corresponding key pairs in the second data frame.
  e.g. rows of DataFileDF with Keys that correspond to the keys of Selected CellsRaw.
  Note this needs to match by key pair MRBTS + LNCEL not each key individually.</p>
  
  <p>I tried:
  SelectedCellsRaw = DataFileDF.loc[DataFileDF['MRBTS'].isin(SelectedCells['MRBTS']) &amp; DataFileDF['LNCEL'].isin(SelectedCells['LNCEL'])]</p>
  
  <p>I get the MRBTS's, but also every occurrence of LNCEL (it has a possible range of 0-9 so there are many duplicates throughout the data set).</p>