tm_map方法错误

Question

I am new in R as well as tm package. My taks is to perform text document classification using decision trees. I am following someone's project. At the page no 14 there is a full code. There are 2 types of documents, which I have loaded using DirSource without any problems. My next step was merging these 2 corpuses into collection

   # Merge corpora into one collection 
docs <- c( wheat.train , crude.train , wheat.test , crude.test ) ;

And then I would like to make some pre-processing.

#pre-processing
docs.p <- docs
docs.p <- tm_map (docs.p, stripWhitespace)

But I got such error

    Error in UseMethod("tm_map", x) : 
  no applicable method for 'tm_map' applied to an object of class "list"

I understand that this guy is using one of the tm's previous version, and currently tm_map takes as an argument a corpus, not a collection of corpuses. My question is how to create such collection of corpuses that it will be possible to perform pre-processing on it?

Answer 1

It worked for me using list instead of c and than lapply .

ex1 <- "bla bla blah   "
ex2 <- "dunno    what else to say    "

wheat <- Corpus(VectorSource(ex1))
crude <- Corpus(VectorSource(ex2))

docs <- list(wheat, crude)
docs.p <- lapply(docs, tm_map, stripWhitespace)