我正在尝试创建一个Hive UDAF来查找最常出现的列(字符串)值(不是单个字符或子字符串,使用精确的列值)。假设以下是我的名为my_table的表(破折号用于直观地分隔列)。
User_Id - Item - Count
1 - A - 1
1 - B - 1
1 - A - 1
1 - A - 1
1 - A - 1
1 - C - 1
2 - C - 1
2 - C - 1
2 - A - 1
2 - C - 1
假设我调用以下脚本:
Select User_Id, findFrequent(*) from my_table group by User_Id
我应该得到以下输出,因为对于User_Id = 1,A出现4次而B和C只出现一次。因此,User_Id = 1的最频繁的一个是A.类似地,User_Id = 2的最频繁的一个是C.换句话说,每个唯一的User_Id应该只有一个最频繁的列值。
1 - A
2 - C
我按照这个例子https://github.com/rathboma/hive-extension-examples/blob/master/src/main/java/com/matthewrathbone/example/TotalNumOfLettersGenericUDAF.java创建了一个类但到目前为止没有运气。这是我的代码:
@Description(name = "FindMostCommonString", value = "_FUNC_(expr) - Returns most commonly found string of a column.")
public class FindMostCommonString extends AbstractGenericUDAFResolver {
@Override
public GenericUDAFEvaluator getEvaluator(TypeInfo[] parameters)
throws SemanticException {
if (parameters.length != 1) {
throw new UDFArgumentTypeException(parameters.length - 1,
"Exactly one argument is expected.");
}
ObjectInspector oi = TypeInfoUtils.getStandardJavaObjectInspectorFromTypeInfo(parameters[0]);
if (oi.getCategory() != ObjectInspector.Category.PRIMITIVE){
throw new UDFArgumentTypeException(0,
"Argument must be PRIMITIVE, but "
+ oi.getCategory().name()
+ " was passed.");
}
PrimitiveObjectInspector inputOI = (PrimitiveObjectInspector) oi;
if (inputOI.getPrimitiveCategory() != PrimitiveObjectInspector.PrimitiveCategory.STRING){
throw new UDFArgumentTypeException(0,
"Argument must be String, but "
+ inputOI.getPrimitiveCategory().name()
+ " was passed.");
}
return new MostCommonStringEvaluator();
}
public static class MostCommonStringEvaluator extends GenericUDAFEvaluator {
PrimitiveObjectInspector inputOI;
ObjectInspector outputOI;
MapObjectInspector mapOI;
HashMap<String, Integer> total = new HashMap<String, Integer>();
@Override
public ObjectInspector init(Mode m, ObjectInspector[] parameters)
throws HiveException {
assert (parameters.length == 1);
super.init(m, parameters);
// init input object inspectors
if (m == Mode.PARTIAL1 || m == Mode.COMPLETE) {
inputOI = (PrimitiveObjectInspector) parameters[0];
}
else{
mapOI = (MapObjectInspector) parameters[0];
}
outputOI = ObjectInspectorFactory.getReflectionObjectInspector(String.class,
ObjectInspectorOptions.JAVA);
return outputOI;
}
static class StringCountAgg implements AggregationBuffer {
HashMap<String, Integer> strCount;
void add(String str){
if(strCount.containsKey(str)){
strCount.put(str,strCount.get(str)+1);
}
else{
strCount.put(str,1);
}
}
StringCountAgg(){
strCount = new HashMap<String, Integer>();
}
}
@Override
public AggregationBuffer getNewAggregationBuffer() throws HiveException {
StringCountAgg result = new StringCountAgg();
return result;
}
@Override
public void reset(AggregationBuffer agg) throws HiveException {
StringCountAgg myagg = new StringCountAgg();
}
private boolean warned = false;
@Override
public void iterate(AggregationBuffer agg, Object[] parameters)
throws HiveException {
assert (parameters.length == 1);
if (parameters[0] != null) {
StringCountAgg myagg = (StringCountAgg) agg;
Object p1 = ((PrimitiveObjectInspector) inputOI).getPrimitiveJavaObject(parameters[0]);
myagg.add((String)p1);
}
}
@Override
public Object terminatePartial(AggregationBuffer agg) throws HiveException {
StringCountAgg myagg = (StringCountAgg) agg;
appendToHashMap(total, myagg.strCount);
return total;
}
@Override
public void merge(AggregationBuffer agg, Object partial)
throws HiveException {
if (partial != null) {
StringCountAgg myagg1 = (StringCountAgg) agg;
HashMap<String, Integer> partialRes = (HashMap<String, Integer> ) mapOI.getMap(partial);
appendToHashMap(myagg1.strCount, partialRes);
}
}
@Override
public Object terminate(AggregationBuffer agg) throws HiveException {
StringCountAgg myagg = (StringCountAgg) agg;
appendToHashMap(total, myagg.strCount);
String result = null;
int maxCount = 0;
for(String key: total.keySet()){
if(total.get(key) > maxCount){
maxCount = total.get(key);
result = key;
}
}
return result;
}
private void appendToHashMap(HashMap<String, Integer> main, HashMap<String, Integer> strCount) {
for(String key: strCount.keySet()){
if(main.containsKey(key)){
main.put(key,main.get(key)+strCount.get(key));
}
else{
main.put(key, strCount.get(key));
}
}
}
}
}
答案 0 :(得分:1)
不确定你被困在哪里但我用这种方法解决了你的问题:
<强> 输入: 强>
yum install java-1.8.0-openjdk java-1.8.0-openjdk-devel
yum install tomcat8-webapps tomcat8-admin-webapps
更新:基于SQL的解决方案: -
hive> Select * from test;
OK
1 A 1
1 B 1
1 A 1
1 A 1
1 A 1
1 C 1
2 C 1
2 C 1
2 A 1
2 C 1
Time taken: 0.15 seconds, Fetched: 10 row(s)
更新:为将来的读者删除了不相关的解决方案
答案 1 :(得分:1)
select User_Id,Item from HiveTable;
+---------+------+
| User_Id | Item |
+---------+------+
| 1 | A |
| 1 | B |
| 1 | A |
| 1 | A |
| 1 | A |
| 1 | C |
| 2 | C |
| 2 | C |
| 2 | C |
| 2 | A |
| 2 | C |
+---------+------+
查询 -
select User_Id, Item from
(
select User_Id,count(*) as total,Item from HiveTable group by User_Id, Item order by total desc
)q3 group by User_Id;
输出
+---------+------+
| User_Id | Item |
+---------+------+
| 1 | A |
| 2 | C |
+---------+------+
希望这会有所帮助