title: R Recommenderlab - Getting the user_id out the RealRatingMatrix containing UBCF recommendations
body: <p>Recommenderlab  - Getting the user_id out the  RealRatingMatrix containing UBCF recommendations.
  I'm trying to use recommenderlab (with RSTUDIO) to get recommendations.When I'm using UBCF I can't extract the user id out of the  realRatingMatrix containing the predictions, although I can do it with POPULAR and IBCF methods.That's the sample code I'm using:</p>
  
  <pre><code>library(recommenderlab)
  data(Jester5k)
  Jester5k
  r &lt;- sample(Jester5k, 1000)   
  rec_pop &lt;- Recommender(Jester5k[1:1000], method = "POPULAR")
  #rec_pop
  recom_pop &lt;- predict(rec_pop, Jester5k[1001:1002], n=100, type="ratings")
  #recom_pop
  as(recom_pop, "matrix")
  getList(recom_pop,decode=TRUE,ratings=TRUE)
  getData.frame(recom_pop,decode=TRUE,ratings=TRUE)
  </code></pre>
  
  <p>user_id and item_id are displayed correctly with each of the 3 alternatives</p>
  
  <pre><code>rec_ib &lt;- Recommender(r[1:100],method="IBCF", param=list(normalize = "Z-score",method="Jaccard",minRating=1))
  #rec_ib
  recom_ib &lt;- predict(rec_ib, Jester5k[1001:1002], n=100, type="ratings")
  #recom_ib    
  as(recom_ib, "matrix")
  getList(recom_ib,decode=TRUE,ratings=TRUE)
  getData.frame(recom_ib,decode=TRUE,ratings=TRUE)
  </code></pre>
  
  <p>user_id and item_id are displayed correctly with each of the 3 alternatives</p>
  
  <pre><code>rec_ub &lt;- Recommender(r[1:400],method="UBCF", param=list(normalize = "Z-score",method="Cosine",nn=5, minRating=1))
  #rec_ub
  recom_ub &lt;- predict(rec_ub, Jester5k[1001:1002], n=100, type="ratings")
  #recom_ub   
  as(recom_ub, "matrix")
  getList(recom_ub,decode=TRUE,ratings=TRUE)
  getData.frame(recom_ub,decode=TRUE,ratings=TRUE)
  </code></pre>
  
  <p>item _id is displayed correctly , but I can't get the user_id with none of the 3 alternatives... How can I get the user_id ?Am I doing something wrong?  I'll appreciate your help to spot my mistake.</p>