title: R, Ways to access matrix elements if missing data is expected
body: <p>I'm coming from a Java/C++ background and just recently started using R for real projects. </p>
  
  <p>One thing I constantly struggle with is matrix (or any type of list/vector/etc.) accession. </p>
  
  <p>Often times I have a set of data stored in a matrix-object and want to extract a row, perform some calculations, and then move on to the next row. 
  However, sometimes I can't just iterate through the matrix-rows but instead need to access them by row-name. </p>
  
  <p>The problem arises, when there is no row of a given name (which tends to happen a lot in the data I'm dealing with). My function simply aborts. </p>
  
  <p>What I'm desperately looking for is to access the matrix-row in a way, where I simply get a 'null'-, 'FALSE'-, whatever-Object, that enables me to continue running the script, even if data is missing. 
  Sure I can check whether my given rowname is part of all matrix-rownames, but that's simply not feasible runtime-wise. </p>