title: how to avoid "Warning message: NAs introduced by coercion" in as.numeric()
body: <p>I have a question on how to avoid <code>NA</code> when using <code>as.numeric</code> function in R.
  As you can see below I have a character variable (but its values are numeric) of <code>cumulative_viewers</code>, 
  and I wanted to convert it to numeric through <code>as.numeric</code> but it did not work properly. 
  The problem is when the number of digits of the numeric values are beyond four digits the <code>as.numeric</code> function returns <code>NA</code> even though the values are numeric.
  For example, <code>as.numeric</code> function work well with the value of '999' or '997' BUT
  when the number of digits are more than four such as '1000' or '1001' or '999999' then the <code>as.numeric</code> function returns <code>NA =.=;;;;;;;;;;;;</code> not its real numeric value....</p>
  
  <p>Could anyone please help me to solve the problem? 
  I sent a day to handle it but could not have an answer yet TT>TT   </p>
  
  <pre><code>paste(data_without_duplicates$cumulative_viewers)
  
      [1] "12,983,336" "12,323,294" "11,375,954" "10,917,221" "10,667,700"
      [6] "10,292,386" "9,350,192"  "9,135,520"  "9,001,309"  "8,653,415" 
      [11] "7,784,755"  "7,508,976"  "7,362,790"  "6,959,047"  "6,706,543" 
      .....
      [1426] "1,026"      "1,024"      "1,023"      "1,020"      "1,017"     
      [1431] "1,016"      "1,013"      "1,011"      "1,001"      "1,000"     
      [1436] "1,000"      "999"        "997"        "994"        "990"       
      [1441] "989"        "988"        "984"        "982"        "979"       
      [1446] "974"        "972"        "971"        "966"        "961"       
  
  
  as.numeric(data_without_duplicates$cumulative_viewers)
  
      [1]  NA  NA  NA  NA  NA  NA  NA  NA  NA  NA  NA  NA  NA  NA  NA  NA  NA
      [18]  NA  NA  NA  NA  NA  NA  NA  NA  NA  NA  NA  NA  NA  NA  NA  NA  NA
      [35]  NA  NA  NA  NA  NA  NA  NA  NA  NA  NA  NA  NA  NA  NA  NA  NA  NA
      .......
      [1395]  NA  NA  NA  NA  NA  NA  NA  NA  NA  NA  NA  NA  NA  NA  NA  NA  NA
      [1412]  NA  NA  NA  NA  NA  NA  NA  NA  NA  NA  NA  NA  NA  NA  NA  NA  NA
      [1429]  NA  NA  NA  NA  NA  NA  NA  NA 999 997 994 990 989 988 984 982 979
      [1446] 974 972 971 966 961 959 958 957 950 946 941 930 929 911 911 910 910
      [1463] 910 907 907 902 898 897 895 892 890 890 889 885 885 883 872 871 868
  </code></pre>