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POimplement customized rawcomparator
 

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  1. POimplement customized rawcomparator
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    <p>i need to improve my MR jobs, one thing i think about is implement a customized rawComparator, however my key class have lots of fields as string besides some int fields, i not sure how to parse out the string fields out of the byte[], </p> <p>my key class</p> <pre><code>public GeneralKey { private int day; private int hour; private String type; private String name; .. } </code></pre> <p>my customized rawComparator:</p> <pre><code>public class GeneralKeyComparator extends WritableComparator { private static final Text.Comparator TEXT_COMPARATOR = new Text.Comparator(); protected GeneralKeyComparator() { super(GeneralKey.class); } @Override public int compare(byte[] b1, int s1, int l1, byte[] b2, int s2, int l2) { int day1 = readInt(b1, s1); int day2 = readInt(b2, s2); int comp = (intDay1 &lt; intDay2) ? -1 : (intDay1 == intDay2) ? 0 : 1; if (0 != comp) { return comp; } int hr1 = readInt(b1, s1+4); int hr2 = readInt(b2, s2+4); comp = (hr1 &lt; hr2) ? -1 : (hr1 == hr2) ? 0 : 1; .... how to compare the String fields here??? return comp; } </code></pre> <p>google around i found people tried this :</p> <pre><code>try { int firstL1 = WritableUtils.decodeVIntSize(b1[s1]) + readInt(b1, s1+8); int firstL2 = WritableUtils.decodeVIntSize(b2[s2]) + readVInt(b2, s2+8); comp = TEXT_COMPARATOR.compare(b1, s1, firstL1, b2, s2, firstL2); } catch (IOException e) { throw new IllegalArgumentException(e); } </code></pre> <p>but i don't understand how this work and don't think it works in my case, anyone can help? thanks</p> <p>added readField() and write() methods here:</p> <pre><code>public void readFields(DataInput input) throws IOException { intDay = input.readInt(); hr = input.readInt(); type = input.readUTF(); name = input.readUTF(); ... } @Override public void write(DataOutput output) throws IOException { output.writeInt(intDay); output.writeInt(hr); output.writeUTF(type); output.writeUTF(name); ... } </code></pre>
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    1. COCan you paste the `readFields` and `write` methods in GeneralKey? How to compare the GeneralKey depends on how you write the GeneralKey to binary.
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      1. POimplement customized rawcomparator
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