title: Change all columns from factor to numeric in R
body: <p>I am working with a big dataset that is causing some trouble because some of the columns I the dataset are being treated as factors. How can I convert all of the columns from factor to numeric, without having to do that column by column??</p>
  
  <p>I have tried to apply a small loop, but it returns NA values. Here's a sample data that applies to the case:</p>
  
  <pre><code>data &lt;- structure(list(v1 = c(22.394, 43.72, 58.544, 56.877, 1.659, 29.142, 
  67.836, 68.851), v2 = c(144.373, 72.3, 119.418, 112.429, 35.779, 
  41.661, 166.941, 126.548), v3 = structure(c(33L, 29L, 33L, 5L, 
  13L, 31L, 5L, 8L), .Label = c("", "#VALUE!", "0", "1", "10", 
  "11", "12", "13", "14", "15", "16", "17", "18", "19", "2", "20", 
  "21", "22", "23", "24", "25", "26", "28", "29", "3", "30", "32", 
  "33", "4", "48", "5", "6", "7", "8", "9"), class = "factor"), 
      v4 = structure(c(24L, 6L, 22L, 23L, 16L, 22L, 23L, 26L), .Label = c("", 
      "-1", "-2", "-4", "#VALUE!", "0", "1", "10", "11", "12", 
      "13", "14", "15", "16", "17", "18", "19", "2", "24", "28", 
      "29", "3", "4", "5", "6", "7", "8", "9"), class = "factor")), .Names = c("v1", 
  "v2", "v3", "v4"), row.names = c("4", "5", "6", "7", "8", "9", 
  "10", "11"), class = "data.frame")
  
  for (i in 1:ncol(data)){
  data[,i] &lt;- as.numeric(as.character(data[i]))
  } ## returns NAs
  </code></pre>
  
  <p>Is there some command that I can apply to turn all these columns into a numeric class?</p>