Some notes:

• The default behavior for the TermDocumentMatrix function from the tm pacakge is that is only tracks words that are longer than three characters.So use control option to specify the wordLenthsi

• If there is some rows without terms in dtm, we should delete them by using:

  rowTotals <- apply(dtm , 1, sum)
  dtm<- dtm[rowTotals> 0, ]

• apps structure is like following:

  str(apps)
  chr [1:17517] "35 44 33 40 33 40 44 38 33 37 37" ... 
  

• There is also a lda test platform writing in shiny.

• After applying LDA to data, we'll get doc distribution over topics, So we try to apply kMean cluster for this distribution.