title: Problem with presidents dataset unable to remove n/a values
body: <pre><code>#presidents is a inbuilt data set in r for time series analysis
  
  
  data("presidents")
   #checking n/a values
  
  colSums(is.na(presidents))
  
  Output 1:
  Error in colSums(is.na(presidents)) : 
    'x' must be an array of at least two dimensions
    checking for data(What is Qtr1,2,3,4(I know it's quarter but is that a label)
  </code></pre>
  
  <p>presidents</p>
  
  <pre><code> Output:
           Qtr1 Qtr2 Qtr3 Qtr4
      1945   NA   87   82   75
      1946   63   50   43   32
      1947   35   60   54   55
      1948   36   39   NA   NA
      1949   69   57   57   51
      1950   45   37   46   39
      1951   36   24   32   23
      1952   25   32   NA   32
      1953   59   74   75   60
      1954   71   61   71   57
      1955   71   68   79   73
      1956   76   71   67   75
      1957   79   62   63   57
      1958   60   49   48   52
      1959   57   62   61   66
      1960   71   62   61   57
      1961   72   83   71   78
      1962   79   71   62   74
      1963   76   64   62   57
      1964   80   73   69   69
      1965   71   64   69   62
      1966   63   46   56   44
      1967   44   52   38   46
      1968   36   49   35   44
      1969   59   65   65   56
      1970   66   53   61   52
      1971   51   48   54   49
      1972   49   61   NA   NA          #NA values are there in it.
      1973   68   44   40   27
      1974   28   25   24   24
  </code></pre>