Consider the Following Mapper Code: 1 #!/Usr/bin/env Python3

question 69

Multiple Choice

Consider the following mapper code: 1 #!/usr/bin/env python3
2 # length_mapper.py
3 """Maps lines of text to key-value pairs of word lengths and 1."""
4 import sys
5
6 def tokenize_input() :
7 """Split each line of standard input into a list of strings."""
8 for line in sys.stdin:
9 yield line.split()
10
11 # read each line in the the standard input and for every word
12 # produce a key-value pair containing the word, a tab and 1
13 for line in tokenize_input() :
14 for word in line:
15 print(str(len(word) ) + '\t1')
Which of the following statements a) , b) or c) is false.

• A) Generator function tokenize_input reads lines of text from the standard input stream and for each returns a list of strings.
• B) When Hadoop executes the script, lines 13-15 iterate through the lists of strings from tokenize_input. For each list (line) and for every string (word) in that list, the script outputs a key-value pair with the word's length as the key, a tab (\t) and the value 1, indicating that there is one word (so far) of that length. Of course, there probably are many words of that length.
• C) The MapReduce algorithm's reduction step will summarize these key-value pairs.
• D) All of the above statements are true.

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