title: count number of columns with the same name R
body: <p>I have a big data frame that in its short version looks like this: </p>
  
  <pre><code>&gt; test
    SRA_Ucon SRA_Uinc SRA_Ucon.1 MID_Rinc MID_Rinc.1 SRA_Ucon.2 MID_cueR MID_Rinc.2 Neut_con Neut_con.1
  1        0        0          0        0          0          0        0          0        0          0
  2        0        0          0        0          0          0        0          0        0          0
  </code></pre>
  
  <p>I want to count the number of columns that start with the same name. For example, in this case, I would like to count number of <strong>SRA_Ucon</strong> columns. There are three of them here. So, I would like to get an output of number "3". What is the optimal way of doing it? </p>