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courses:mapreduce-tutorial:step-29 [2012/02/05 18:54] straka |
courses:mapreduce-tutorial:step-29 [2012/02/05 18:57] straka |
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| In a reduce, it is guaranteed that keys are processed in ascending order. Sometimes it would be useful if the //values associated with one key// could also be processed in ascending order. | In a reduce, it is guaranteed that keys are processed in ascending order. Sometimes it would be useful if the //values associated with one key// could also be processed in ascending order. | ||
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| + | That is possible only to some degree. The (key, value) pairs are compared //using the key only//. After the (key, value) pairs are sorted, the (key, value) pairs with the same key are //grouped// together. This grouping can be performed using a custom '' | ||
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