title: how do you subset a data frame based on column names?
body: <p>I have this data frame:</p>
  
  <pre><code> dput(df)
  structure(list(Server = structure(c(1L, 1L, 1L, 1L, 1L, 1L), .Label = "servera", class = "factor"), 
      Date = structure(1:6, .Label = c("7/13/2017 15:01", "7/13/2017 15:02", 
      "7/13/2017 15:03", "7/13/2017 15:04", "7/13/2017 15:05", 
      "7/13/2017 15:06"), class = "factor"), Host_CPU = c(1.812950134, 
      2.288070679, 1.563278198, 1.925239563, 5.350669861, 2.612503052
      ), UsedMemPercent = c(38.19, 38.19, 38.19, 38.19, 38.19, 
      38.22), jvm1 = c(10.91, 11.13, 11.34, 11.56, 11.77, 11.99
      ), jvm2 = c(11.47, 11.7, 11.91, 12.13, 12.35, 12.57), jvm3 = c(75.65, 
      76.88, 56.93, 58.99, 65.29, 67.97), jvm4 = c(39.43, 40.86, 
      42.27, 43.71, 45.09, 45.33), jvm5 = c(27.42, 29.63, 31.02, 
      32.37, 33.72, 37.71)), .Names = c("Server", "Date", "Host_CPU", 
  "UsedMemPercent", "jvm1", "jvm2", "jvm3", "jvm4", "jvm5"), class = "data.frame", row.names = c(NA, 
  -6L))
  </code></pre>
  
  <p>I only want to be able to subset this data frame based on the vectors names in this variable:</p>
  
  <pre><code>select&lt;-c("jvm3", "jvm4", "jvm5")
  </code></pre>
  
  <p>so, my final df should look like this:</p>
  
  <pre><code>structure(list(Server = structure(c(1L, 1L, 1L, 1L, 1L, 1L), .Label = "servera", class = "factor"), 
      Date = structure(1:6, .Label = c("7/13/2017 15:01", "7/13/2017 15:02", 
      "7/13/2017 15:03", "7/13/2017 15:04", "7/13/2017 15:05", 
      "7/13/2017 15:06"), class = "factor"), Host_CPU = c(1.812950134, 
      2.288070679, 1.563278198, 1.925239563, 5.350669861, 2.612503052
      ), UsedMemPercent = c(38.19, 38.19, 38.19, 38.19, 38.19, 
      38.22), jvm3 = c(75.65, 76.88, 56.93, 58.99, 65.29, 67.97
      ), jvm4 = c(39.43, 40.86, 42.27, 43.71, 45.09, 45.33), jvm5 = c(27.42, 
      29.63, 31.02, 32.37, 33.72, 37.71)), .Names = c("Server", 
  "Date", "Host_CPU", "UsedMemPercent", "jvm3", "jvm4", "jvm5"), class = "data.frame", row.names = c(NA, 
  -6L))
  </code></pre>
  
  <p>any ideas?</p>