We have n machines, each having 10 n memory space. The input is a set of items (

Question

We have n machines, each having 10n memory space. The input is a set of items (i; vi), for i = 1, 2, . . . , n,
distributed in an arbitrary order among the n machines. We want to compute the output (i; Pji vj), for
i = 1, . . . , n. The n output pairs can also be distributed in an arbitrary order on the n machines. Please
design a MapReduce algorithm to solve this problem in constant number of rounds (the fewer the better).
Please specify the followings at each round:
• The Map function in the format of
(key; value) (key1; value1), (key2; value2), . . .
• The Reduce function in the format of
(key; value1), (key; value2), . . . (key1; value1), (key2; value2), . . .

Explanation / Answer

>>> d = {'key1': 'value1', 'key2': 'value2'} >>> ['{}_{}'.format(k,v) for k,v in d.iteritems()] ['key2_value2', 'key1_value1'] def checkCommonNodes(id, rs): id_key, id_value = id.split('_') for r in rs: try: if r[id_key] == id_value: print "".join('{}_{}'.format(k,v) for k,v in r.iteritems()) except KeyError: continue or(String kvPair: kvPairs) { String[] kv = kvPair.split("="); String key = kv[0]; String value = kv[1]; // Now do with key whatever you want with key and value... if(key.equals("specialkey")) { // Do something with value if the key is "specialvalue"... } }

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