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)) + ' 1')
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 ( ) 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.

Question

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)) + '	1')
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 (	) 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.

Quizplus · Accepted Answer

A) The statement is true. The function tokenize_input reads lines from standard input and returns a list of strings after splitting each line on whitespaces.
B) The statement is true. For every word in the input, the mapper outputs a key-value pair with the length of the word as the key and 1 as the value. This is a typical mapper function in a MapReduce job.
C) The statement is true. In the MapReduce algorithm, the reduction step takes each key-value pair with the same key and summarizes them to produce a final output. In this case, the reducer could sum the number of ones to count the total number of words of a given length.

Therefore, all of the stated statements are true.

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