我是r的新手，我对mapreduce rmr2有问题。我有一个这样的文件要读，每一行都有一个日期和一些单词（a，b，c…）：

2016-05-10, A, B, C, A, R, E, F, E
2016-05-18, A, B, F, E, E
2016-06-01, A, B, K, T, T, E, G, E, A, N
2016-06-03, A, B, K, T, T, E, F, E, L, T

我想在输出中得到如下结果：

2016-05: A 3 
2016-05: E 4
2016-05: E 4

我在java实现中也做过同样的问题，现在我也要在r代码中做同样的问题，但我必须弄清楚如何做我的reducer。有一种方法可以在mapper和reduce代码中进行一些打印，因为在mapper或reduce中使用print命令，会在rstudio中获得错误

Sys.setenv(HADOOP_STREAMING = "/usr/local/hadoop/share/hadoop/tools/lib/hadoop-streaming-2.8.0.jar")
Sys.setenv(HADOOP_HOME = "/usr/local/hadoop/bin/hadoop")
Sys.setenv(HADOOP_CMD = "/usr/local/hadoop/bin/hadoop") 
library(stringr)
library(rmr2)
library(stringi)
customMapper = function(k,v){
  #words = unlist(strsplit(v,"\\s"))
  #words = unlist(strsplit(v,","))
  tmp = unlist(stri_split_fixed(v, pattern= ",",n = 2))
  data = tmp[1]
  onlyYearMonth = unlist(stri_split_fixed(data, pattern= "-",n = 3))
  #print(words)
  words = unlist(strsplit(tmp[2],","))
  compositeK = paste(onlyYearMonth[1],"-",onlyYearMonth[2])
  keyval(compositeK,words)
}
customReducer = function(k,v) {
    #Here there are all the value with same date ??? 
    elementsWithSameDate = unlist(v)
    #defining something similar to java Map to use for counting elements in same date
    # myMap
    for(elWithSameDate in  elementsWithSameDate) {
      words = unlist(strsplit(elWithSameDate,","))
      for(word in words) {
        compositeNewK = paste(k,":",word)
        # if myMap contains compositeNewK
             # myMap (compositeNewK, 1 + myMap.getValue(compositeNewK))
        # else 
             #myMap (compositeNewK, 1)
      }
    }
    #here i want to transorm myMap in a String, containing the first 3 words with max occurrencies
    #fromMapToString = convert(myMap)
    keyval(k,fromMapToString)
}
wordcount = function(inputData,outputData=NULL){
  mapreduce(input = inputData,output = outputData,input.format = "text",map = customMapper,reduce = customReducer)
}
hdfs.data = file.path("/user/hduser","folder2")
hdfs.out  = file.path("/user/hduser","output1")
result = wordcount(hdfs.data,hdfs.out)