fusionfil<-function(ruta){
  require(data.table)
  fusionfrag<-paste0(ruta,grep("_filt",dir(ruta),value = TRUE))

  datalist<-list()

  for(frag in fusionfrag){
    datalist[[frag]] <- fread(frag,colClasses="character")
  }

  datalist<-do.call(rbind,datalist)

  fwrite(datalist,"fusion.csv")
}

Warning messages:
1: In rbindlist(l, use.names, fill, idcol) :
  Reached total allocation of 8082Mb: see help(memory.size)
2: In rbindlist(l, use.names, fill, idcol) :
  Reached total allocation of 8082Mb: see help(memory.size)