title: Converting Data frame to time series in R
body: <p>I currently have this data set below, but I am unsure as to how I can convert this into a time series from the data frame format that it is currently in. </p>
  
  <p>I am also unsure as to how I can split this data up to create an in-sample and out-of-sample data set for forecasting.</p>
  
  <pre><code>      Date Observations
  1  1975/01         5172
  2  1975/02         6162
  3  1975/03         6979
  4  1975/04         5418
  5  1976/01         4801
  6  1976/02         5849
  7  1976/03         6292
  8  1976/04         5261
  9  1977/01         4461
  10 1977/02         5322
  11 1977/03         6153
  12 1977/04         5377
  13 1978/01         4808
  14 1978/02         5845
  15 1978/03         6023
  16 1978/04         5691
  17 1979/01         4683
  18 1979/02         5663
  19 1979/03         6068
  20 1979/04         5429
  21 1980/01         4897
  22 1980/02         5685
  23 1980/03         5862
  24 1980/04         4663
  25 1981/01         4566
  26 1981/02         5118
  27 1981/03         5261
  28 1981/04         4459
  29 1982/01         4352
  30 1982/02         4995
  31 1982/03         5559
  32 1982/04         4823
  33 1983/01         4462
  34 1983/02         5228
  35 1983/03         5997
  36 1983/04         4725
  37 1984/01         4223
  38 1984/02         4940
  39 1984/03         5780
  40 1984/04         5232
  41 1985/01         4723
  42 1985/02         5219
  43 1985/03         5855
  44 1985/04         5613
  45 1986/01         4987
  46 1986/02         6117
  47 1986/03         5777
  48 1986/04         5803
  49 1987/01         5113
  50 1987/02         6298
  51 1987/03         7152
  52 1987/04         6591
  53 1988/01         6337
  54 1988/02         6672
  55 1988/03         7224
  56 1988/04         6296
  57 1989/01         6957
  58 1989/02         7538
  59 1989/03         8022
  60 1989/04         7216
  61 1990/01         6633
  62 1990/02         7355
  63 1990/03         7897
  64 1990/04         7159
  65 1991/01         6637
  66 1991/02         7629
  67 1991/03         8080
  68 1991/04         7077
  69 1992/01         7190
  70 1992/02         7396
  71 1992/03         7795
  72 1992/04         7147
  </code></pre>