猪群中地图的组合键值 [英] Group key value of map in pig
问题描述
[a#1,b#2,c#3]
[ 4,b#5,c#6]
[a#7,b#8,c#9]
猪脚本
A = LOAD'txt'AS(in:map []);
B = FOREACH A GENERATE in#'a';
DUMP B
我们知道我们可以把值放在钥匙中。在上面的例子中,我拿到了包含关键字a的值的地图。
假设我不知道密钥,我想对关系中的密钥进行分组,并将其转储。
(a,{1,4,7})
(b,{2,5,8})
(c,{3,6,9})
猪是否允许这样的操作或需要使用UDF?请帮我通过这个。谢谢。
您可以创建一个自定义的 UDF
到一个包(使用Pig v0.10.0):
package com.example;
import java.io.IOException;
import java.util.Map;
import java.util.Map.Entry;
import org.apache.pig.EvalFunc;
import org.apache.pig.data.BagFactory;
import org.apache.pig.data.DataBag;
import org.apache.pig.data.Tuple;
import org.apache.pig.data.TupleFactory;
public class MapToBag扩展EvalFunc< DataBag> {
private static final BagFactory bagFactory = BagFactory.getInstance();
private static final TupleFactory tupleFactory = TupleFactory.getInstance();
@Override
public DataBag exec(Tuple input)throws IOException {
try {
@SuppressWarnings(unchecked)
Map< String,Object> ; map =(Map< String,Object>)input.get(0);
DataBag result = null;
if(map!= null){
result = bagFactory.newDefaultBag(); $($条目< String,Object>条目:map.entrySet())
{
元组tuple = tupleFactory.newTuple(2);
tuple.set(0,entry.getKey());
tuple.set(1,entry.getValue());
result.add(tuple);
}
}
返回结果;
}
catch(异常e){
抛出新的RuntimeException(MapToBag错误,e);
}
}
}
然后:
B = foreach A生成
flatten(com.example.MapToBag(in))as(k:chararray,v:chararray) ;
描述B;
B:{k:chararray,v:chararray}
现在按键分组一个嵌套的foreach:
C = foreach(B组由k){
value = foreach B generate v;
生成组作为键,值;
};
dump C;
(a,{(1),(4),(7)})
(b,{(2),(5),(8)})
(c, (3),(6),(9)})
I am new to pigscript. Say, We have a file
[a#1,b#2,c#3]
[a#4,b#5,c#6]
[a#7,b#8,c#9]
pig script
A = LOAD 'txt' AS (in: map[]);
B = FOREACH A GENERATE in#'a';
DUMP B;
We know that we can take the values feeding in the key. In the above example I took the map that contains the values with respect to the key "a". Assuming that I dont know the key, I want to group the values with respect to keys in a relation and dump it.
(a,{1,4,7})
(b,{2,5,8})
(c,{3,6,9})
Does pig allows such operations or need to go with UDF? Please help me through this. Thanks.
You can create a custom UDF
which converts the map to a bag (using Pig v0.10.0):
package com.example;
import java.io.IOException;
import java.util.Map;
import java.util.Map.Entry;
import org.apache.pig.EvalFunc;
import org.apache.pig.data.BagFactory;
import org.apache.pig.data.DataBag;
import org.apache.pig.data.Tuple;
import org.apache.pig.data.TupleFactory;
public class MapToBag extends EvalFunc<DataBag> {
private static final BagFactory bagFactory = BagFactory.getInstance();
private static final TupleFactory tupleFactory = TupleFactory.getInstance();
@Override
public DataBag exec(Tuple input) throws IOException {
try {
@SuppressWarnings("unchecked")
Map<String, Object> map = (Map<String, Object>) input.get(0);
DataBag result = null;
if (map != null) {
result = bagFactory.newDefaultBag();
for (Entry<String, Object> entry : map.entrySet()) {
Tuple tuple = tupleFactory.newTuple(2);
tuple.set(0, entry.getKey());
tuple.set(1, entry.getValue());
result.add(tuple);
}
}
return result;
}
catch (Exception e) {
throw new RuntimeException("MapToBag error", e);
}
}
}
Then:
B = foreach A generate
flatten(com.example.MapToBag(in)) as (k:chararray, v:chararray);
describe B;
B: {k: chararray,v: chararray}
Now group by key and use a nested foreach:
C = foreach (group B by k) {
value = foreach B generate v;
generate group as key, value;
};
dump C;
(a,{(1),(4),(7)})
(b,{(2),(5),(8)})
(c,{(3),(6),(9)})
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