title: Concatenating two vectors in R
body: <p>I want to concatenate two vectors one after the other in R. I have written the following code to do it:  </p>
  
  <pre><code>&gt; a = head(tracks_listened_train)
  &gt; b = head(tracks_listened_test)
  &gt; a
  [1] cc1a46ee0446538ecf6b65db01c30cd8 19acf9a5cbed34743ce0ee42ef3cae3e
  [3] 9e7fdbf2045c9f814f6c0bed5da9bed7 3441b1031267fbb6009221bf47f9c5e8
  [5] 206c8b79bd02beeea200879afc414879 1a7a95e3845a6815060628e847d14362
  18585 Levels: 0001a423baf29add84af6ec58aeb5b90 ...
  &gt; b
  [1] 7251a7694b79aa9a39f9a1a5f5c8a253 2f362377ef0e7bca112233fdda22a79c
  [3] c1196625b1b733b62c43935334e1d190 58e41e462af4185b08231a41453c3faf
  [5] 1cc2517fa9c037e02a14ce0950a28f67
  10186 Levels: 0001a423baf29add84af6ec58aeb5b90 ...
  &gt; res = c(a,b)
  &gt; res
  [1] 14898  1898 11556  3859  2408  1950  4473  1865  7674  3488  1130
  </code></pre>
  
  <p>However, I get the unexpected result of the resultant vector. What could the problem be? </p>