Changes between Version 2 and Version 3 of waue/2009/0716

Timestamp:

Jul 16, 2009, 5:47:29 PM (15 years ago)

Author:

waue

Comment:

--

waue/2009/0716

@@ -4 +4 @@
  原因：Type mismatch in key from map: expected org.apache.hadoop.io.LongWritable, recieved org.apache.hadoop.io.Text 
 
- Map的key從LongWritable 強制轉型到 String，似乎會遇到一些錯
+ Map 的 key 從 longWritable 強制轉型到 String，似乎會遇到一些錯
 
  * keyvalue.java
@@ -20 +20 @@
 public class keyvalue{
         public static void main(String[] args) {
-                String[] argv = {"input","oh9","1","1"};
+                String[] argv = {"input","output","1","1"};
                 args = argv;
                 
@@ -53 +53 @@
 
 {{{
-#!java
+
 package nchc.keyvalue;
 
@@ -81 +81 @@
 
 {{{
-#!java
+
 package nchc.keyvalue;
 
@@ -106 +106 @@
 }
 }}}
+
+----------
+改成以下的map 與 reduce 檔就可以正常運作
+
+ * kvM.java
+
+{{{
+#!java
+package nchc.keyvalue;
+
+import java.io.IOException;
+
+import org.apache.hadoop.io.LongWritable;
+import org.apache.hadoop.io.Text;
+import org.apache.hadoop.mapred.MapReduceBase;
+import org.apache.hadoop.mapred.Mapper;
+import org.apache.hadoop.mapred.OutputCollector;
+import org.apache.hadoop.mapred.Reporter;
+
+public class kvM extends MapReduceBase implements
+                Mapper<LongWritable, Text, LongWritable, Text> {
+
+        public void map(LongWritable key, Text value,
+                        OutputCollector<LongWritable, Text> output, Reporter report)
+                        throws IOException {
+                output.collect(key, value);
+        }
+
+}
+}}}
+
+ * kvR.java
+
+{{{
+#!java
+package nchc.keyvalue;
+
+import java.io.IOException;
+import java.util.Iterator;
+
+import org.apache.hadoop.io.LongWritable;
+import org.apache.hadoop.io.Text;
+import org.apache.hadoop.mapred.MapReduceBase;
+import org.apache.hadoop.mapred.OutputCollector;
+import org.apache.hadoop.mapred.Reducer;
+import org.apache.hadoop.mapred.Reporter;
+
+public class kvR extends MapReduceBase implements
+                Reducer< LongWritable, Text, Text, Text> {
+        public void reduce(LongWritable key, Iterator<Text> values,
+                        OutputCollector<Text, Text> output, Reporter report)
+                        throws IOException {
+                while (values.hasNext()) {
+                        Text keyv = new Text("< "+key+" , ");
+                        Text val = new Text(values.next()+">");
+                        output.collect(keyv, val);
+                }
+        }
+}
+}}}
+
+然而就看不到key被reduce起來
+
+ * output/part-00000
+{{{
+< 0 ,   This eBook is for the use of anyone anywhere at no cost and with>
+< 0 ,   This eBook is for the use of anyone anywhere at no cost and with>
+< 66 ,  almost no restrictions whatsoever.  You may copy it, give it away or>
+< 66 ,  almost no restrictions whatsoever.  You may copy it, give it away or>
+< 136 ,         re-use it under the terms of the Project Gutenberg License included>
+< 136 ,         re-use it under the terms of the Project Gutenberg License included>
+< 205 ,         with this eBook or online at www.gutenberg.net>
+< 205 ,         with this eBook or online at www.gutenberg.org>
+
+.... (省略)
+}}}