title: Converting factors consisting of multiple numbers to numeric
body: <p>Converting factors to numeric has been dealt with multiple times, but my issue is when I have multiple numbers within the factor. For instance, here is a small subset of my data.frame:</p>
  
  <pre><code>                    AF      AC   AN   EAS_AF         AMR_AF
  1          0.000199681       1 5008    0.001            0.0
  2           0.00319489      16 5008      0.0            0.0
  3 0.024361, 0.00479233 122, 24 5008 0.0, 0.0 0.0043, 0.0014
  4           0.00439297      22 5008      0.0         0.0014
  5          0.000798722       4 5008      0.0            0.0
  </code></pre>
  
  <p>Normally I would use the <code>as.numeric</code> and <code>levels</code> functions in combination to convert these factors into numbers. However, row three has two numbers in each entry, and therefore I get an NA when attempting this method on these variables. Is there any way to get round this? I have too many of these such cases to manually pluck them out.</p>
  
  <p>My overall objective is to test whether each entry in each of these columns is greater than 0 (so if there are two numbers, I would test both), which is why I am attempting to convert into numeric in the first place. If there is any other smarter way around this problem I'd be willing to try it.</p>
  
  <p>As requested, below is the <code>dput</code> of a reduced version of my data frame (taking only the first 10 rows).</p>
  
  <pre><code>structure(list(CHROM = c(10L, 10L, 10L, 10L, 10L, 10L, 10L, 10L, 
  10L), POS = c(180109L, 209892L, 221335L, 239445L, 246927L, 246928L, 
  246933L, 246955L, 246970L), ID = structure(c(6L, 4L, 1L, 3L, 
  5L, 9L, 2L, 7L, 8L), .Label = c("rs143013573", "rs1431845", "rs145483680", 
  "rs151111729", "rs547339499", "rs547699134", "rs556577288", "rs575589407", 
  "rs72770983"), class = "factor"), REF = structure(c(3L, 2L, 2L, 
  3L, 1L, 1L, 3L, 2L, 1L), .Label = c("A", "C", "G"), class = "factor"), 
      ALT = structure(c(1L, 2L, 3L, 1L, 2L, 2L, 1L, 4L, 2L), .Label = c("A", 
      "G", "G, T", "T"), class = "factor"), AF = structure(c(1L, 
      5L, 7L, 6L, 2L, 4L, 8L, 3L, 1L), .Label = c("0.000199681", 
      "0.000798722", "0.000998403", "0.00239617", "0.00319489", 
      "0.00439297", "0.024361, 0.00479233", "0.220248"), class = "factor"), 
      AC = structure(c(1L, 5L, 4L, 6L, 7L, 3L, 2L, 8L, 1L), .Label = c("1", 
      "1103", "12", "122, 24", "16", "22", "4", "5"), class = "factor"), 
      AN = c(5008L, 5008L, 5008L, 5008L, 5008L, 5008L, 5008L, 5008L, 
      5008L), EAS_AF = structure(c(3L, 1L, 2L, 1L, 1L, 3L, 4L, 
      1L, 1L), .Label = c("0.0", "0.0, 0.0", "0.001", "0.248"), class = "factor"), 
      AMR_AF = structure(c(1L, 1L, 3L, 2L, 1L, 2L, 4L, 1L, 2L), .Label = c("0.0", 
      "0.0014", "0.0043, 0.0014", "0.1599"), class = "factor"), 
      AFR_AF = structure(c(1L, 3L, 5L, 4L, 2L, 1L, 6L, 1L, 1L), .Label = c("0.0", 
      "0.003", "0.0121", "0.0159", "0.09, 0.0", "0.1611"), class = "factor"), 
      EUR_AF = structure(c(1L, 1L, 2L, 1L, 1L, 3L, 4L, 1L, 1L), .Label = c("0.0", 
      "0.0, 0.0089", "0.0089", "0.2495"), class = "factor"), SAS_AF = structure(c(1L, 
      1L, 2L, 1L, 1L, 3L, 5L, 4L, 1L), .Label = c("0.0", "0.0, 0.0143", 
      "0.001", "0.0051", "0.2843"), class = "factor"), consequence = structure(c(2L, 
      1L, 2L, 2L, 2L, 2L, 2L, 2L, 2L), .Label = c("stop_gained", 
      "synonymous_variant"), class = "factor"), gene = structure(c(1L, 
      1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L), .Label = "ZMYND11", class = "factor"), 
      accession = structure(c(1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L
      ), .Label = "NM_006624.5", class = "factor"), gene_type = structure(c(1L, 
      1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L), .Label = "protein_coding", class = "factor")), .Names = c("CHROM", 
  "POS", "ID", "REF", "ALT", "AF", "AC", "AN", "EAS_AF", "AMR_AF", 
  "AFR_AF", "EUR_AF", "SAS_AF", "consequence", "gene", "accession", 
  "gene_type"), class = "data.frame", row.names = c(NA, -9L)) 
  </code></pre>