自定义Hive UDAF 实现相邻去重

内置的两个聚合函数（UDAF）

collect_list()：多行字符串拼接为一行
collect_set()：多行字符串拼接为一行并去重
多行字符串拼接为一行并相邻去重UDAF：Concat()

concat_udaf.jar

package com.tcc.udaf;

import org.apache.hadoop.hive.ql.exec.UDAF;
import org.apache.hadoop.hive.ql.exec.UDAFEvaluator;

public class Concat extends UDAF
{
public static class ConcatUDAFEvaluator
implements UDAFEvaluator
{
private PartialResult partial;

public void init()
{
this.partial = null;
}

public boolean iterate(String value, String deli)
{
if (value == null) {
return true;
}
if (this.partial == null) {
this.partial = new PartialResult();
this.partial.result = new String("");
if ((deli == null) || (deli.equals("")))
{
this.partial.delimiter = new String(",");
}
else
{
this.partial.delimiter = new String(deli);
}
}

if (this.partial.result.length() > 0)
{
this.partial.result = this.partial.result.concat(this.partial.delimiter);
}

this.partial.result = this.partial.result.concat(value);

return true;
}

public PartialResult terminatePartial() {
return this.partial;
}

public boolean merge(PartialResult other) {
if (other == null) {
return true;
}
if (this.partial == null) {
this.partial = new PartialResult();
this.partial.result = new String(other.result);
this.partial.delimiter = new String(other.delimiter);
}
else
{
if (this.partial.result.length() > 0)
{
this.partial.result = this.partial.result.concat(this.partial.delimiter);
}
this.partial.result = this.partial.result.concat(other.result);
}
return true;
}

public String terminate() {
String s = new String(this.partial.result);

if (s.indexOf(this.partial.delimiter) != -1) {
String[] str = s.split(this.partial.delimiter);

StringBuffer sb = new StringBuffer();

int i = 0; int j = 1;
while (i < str.length - 1) {
while (j < str.length) {
if (str[j].equals(str[i])) {
if (j == str.length - 1) {
sb.append(str[i]);
break;
}
j++;
} else {
sb.append(str[i]);
sb.append(this.partial.delimiter);
break;
}
}
i = j;
j = i + 1;
}
if ((i == str.length - 1) && (!str[i].equals(str[(i - 1)]))) {
sb.append(str[i]);
}
return sb.toString();
}
return s;
}

public static class PartialResult
{
String result;
String delimiter;
}
}
}

使用：

add jar concat_udaf.jar;
create temporary function Concat as 'com.tcc.udaf.Concat';
select a,concat(b,',') from concat_test group by a;
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转自：https://me.csdn.net/chuangchuangtao
原文链接：https://blog.csdn.net/chuangchuangtao/article/details/77455675