title: Change the Blank Cells to "NA"
body: <p>Here's the <a href="https://www.dropbox.com/s/ttwiitihjtb7mec/data2.csv">link</a> of my data. </p>
  
  <p>My target is to assign "NA" to all blank cells irrespective of categorical or numerical values. I am using <strong>na.strings=""</strong>. But it's not assigning NA to all blank cells.</p>
  
  <pre><code>## reading the data
  dat &lt;- read.csv("data2.csv")
  head(dat)
    mon hr        acc   alc sex spd axles door  reg                                 cond1 drug1
  1   8 21 No Control  TRUE   F   0     2    2      Physical Impairment (Eyes, Ear, Limb)     A
  2   7 20 No Control FALSE   M 900     2    2                                Inattentive     D
  3   3  9 No Control FALSE   F 100     2    2 2004                                Normal     D
  4   1 15 No Control FALSE   M   0     2    2      Physical Impairment (Eyes, Ear, Limb)     D
  5   4 21 No Control FALSE      25    NA   NA                                                D
  6   4 20 No Control    NA   F  30     2    4                Drinking Alcohol - Impaired     D
         inj1 PED_STATE st rac1
  1     Fatal      &lt;NA&gt;  F &lt;NA&gt;
  2  Moderate      &lt;NA&gt;  F &lt;NA&gt;
  3  Moderate      &lt;NA&gt;  M &lt;NA&gt;
  4 Complaint      &lt;NA&gt;  M &lt;NA&gt;
  5 Complaint      &lt;NA&gt;  F &lt;NA&gt;
  6  Moderate      &lt;NA&gt;  M &lt;NA&gt;
  
  
  ## using na.strings
  dat2 &lt;- read.csv("data2.csv", header=T, na.strings="")
  head(dat2)
    mon hr        acc   alc sex spd axles door  reg                                 cond1 drug1
  1   8 21 No Control  TRUE   F   0     2    2 &lt;NA&gt; Physical Impairment (Eyes, Ear, Limb)     A
  2   7 20 No Control FALSE   M 900     2    2 &lt;NA&gt;                           Inattentive     D
  3   3  9 No Control FALSE   F 100     2    2 2004                                Normal     D
  4   1 15 No Control FALSE   M   0     2    2 &lt;NA&gt; Physical Impairment (Eyes, Ear, Limb)     D
  5   4 21 No Control FALSE      25    NA   NA &lt;NA&gt;                                  &lt;NA&gt;     D
  6   4 20 No Control    NA   F  30     2    4 &lt;NA&gt;           Drinking Alcohol - Impaired     D
         inj1 PED_STATE st rac1
  1     Fatal        NA  F   NA
  2  Moderate        NA  F   NA
  3  Moderate        NA  M   NA
  4 Complaint        NA  M   NA
  5 Complaint        NA  F   NA
  6  Moderate        NA  M   NA
  </code></pre>