title: Average over list by row in R
body: <p>I have a dataframe with measurements stored as a list by row. </p>
  
  <pre><code>  Subject                 Measurements
  1      s1  -0.4, -0.9, -1.1, -0.1,  0.1
  2      s2  -1.4, -1.7, -1.7, -0.6, -1.7
  3      s3  -1.0, -0.1, -0.6, -0.5, -0.1
  4      s4  -0.2, -0.5, -0.2,  0.1, -0.7
  5      s5   0.7,  0.2,  0.4,  0.7,  0.2
  6      s6  -0.3, -0.1,  0.1, -0.2, -0.1
  </code></pre>
  
  <p>How do I average/find standard deviation/other list manipulations and add the output to a new column in data frame (e.g "mean")</p>
  
  <p><strong>Edit</strong> </p>
  
  <p>Here's the data structure I'm working with:</p>
  
  <pre><code>structure(list(Subject = structure(1:6, .Label = c("s1", "s2", 
  "s3", "s4", "s5", "s6"), class = "factor"), Measurements = list(
  c(-0.4, -0.9, -1.1, -0.1, 0.1), c(-1.4, -1.7, -1.7, -0.6, 
  -1.7), c(-1, -0.1, -0.6, -0.5, -0.1), c(-0.2, -0.5, -0.2, 
  0.1, -0.7), c(0.7, 0.2, 0.4, 0.7, 0.2), c(-0.3, -0.1, 0.1, 
  -0.2, -0.1))), .Names = c("Subject", "Measurements"), row.names = c(NA, 
  6L), class = "data.frame")
  </code></pre>