RHive example code

• Example 1
  how to connect and execute HQL (HiveQL)
  

  
  rhive.connect("10.10.10.1")  # 10.10.10.1 is the IP address of hiveserver
  rhive.query("select * from emp")
  

• Example 2
  how to use RUDF like scalar function and export R Object
  

  
  coefficient <- 1.1
  scoring <- function(sal) {
      coefficient * sal
  }
  rhive.assign('coefficient',coefficient)
  rhive.assign('scoring',scoring)
  rhive.exportAll(‘scoring’)
  rhive.query("select R('scoring',col_sal,0.0) from emp")
  

• Example 3
  how to use RUDAF like aggregation function
  

  
  hsum <- function(prev,sal) {
     if(is.null(prev)) {
        sal <- c(0)  
        return(sal)
     }
     return(prev + sal)
  }
  hsum.partial <- function(agg_sal) {
     agg_sal
  }
  hsum.merge <- function(prev, agg_sal) {
      if(is.null(prev))
           agg_sal
      else
           prev + agg_sal
  }
  hsum.terminate <- function(agg_sal) {
      return(agg_sal)
  }
  rhive.assign('hsum',hsum)
  rhive.assign('hsum.partial',hsum.partial)
  rhive.assign('hsum.merge',hsum.merge)
  rhive.assign('hsum.terminate',hsum.terminate)
  rhive.exportAll('hsum')
  rhive.query("select RA('hsum',sal) from emp group by empno")
  

• Example 4
  how to manipulate Hive table using RHive API
  

  
  emp <- rhive.desc.table(‘emp’)
  colnames(emp)
  </pre>

• Example 5
  how to use custom Map/Reduce script in RHive
  

  
  map <- function(key,value) {
       if(is.null(value)) {
           put(NA,1)
       }
       lapply(value, function(column) {
           lapply(strsplit(x=column, split=" ")[[[[1]]]], function(word) put(word,1))
       })
  }
  reduce <- function(key, values) {
      put(key, sum(as.numeric(values)))
  }
  rhive.mrapply("emp", map, reduce, c("ename", "position"), c("word", "one"), by="word", c("word", "one"), c("word", "count"))
  

• Example 6
  how to export R data object to Hive
  

  
  tablename <- rhive.write.table(USArrests)
  rhive.desc.table(tablename)
  rhive.load.table(tablename)