Return to Video

Finding Mean - Intro to Hadoop and MapReduce

  • 0:00 - 0:02
    So let's do it. Let's calculate mean
  • 0:02 - 0:04
    and standard deviation. And to do that, let's
  • 0:04 - 0:08
    think back to our example with stores and
  • 0:08 - 0:11
    sales. And let's say the question we want to
  • 0:11 - 0:15
    answer is, is there any correlation between the
  • 0:15 - 0:18
    day of the week and how much money
  • 0:18 - 0:22
    people spend on various items? And what's interesting
  • 0:22 - 0:25
    about this design pattern is that all the
  • 0:25 - 0:31
    mapper has to do is, I'll put the day of the week as a key, so maybe Monday, and
  • 0:31 - 0:35
    the value of a sale, maybe $5.20 as a value.
  • 0:35 - 0:38
    That's it. What does that leave for the reducer? Well,
  • 0:38 - 0:42
    it leaves all the math for the reducer. And the
  • 0:42 - 0:44
    general reason for this rule of thumb, for what the
  • 0:44 - 0:46
    mapper and reducer are doing, comes from the fact that
  • 0:46 - 0:51
    oftentimes with these, with these summary statistics, you sort of need
  • 0:51 - 0:53
    to know all of the statistics or all of
  • 0:53 - 0:56
    the parent data before you can make any calculations. So
  • 0:56 - 0:58
    we don't want to jump the gun and have the mapper
  • 0:58 - 1:01
    do calculations before it's ready. So why don't you go
  • 1:01 - 1:04
    ahead and calculate the mean and standard deviation for
  • 1:04 - 1:07
    sales for each day of the week, to help us
  • 1:07 - 1:11
    try to answer this question. If there's any correlation between
  • 1:11 - 1:13
    the day of the week and how much people spend.
Tytuł:
Finding Mean - Intro to Hadoop and MapReduce
Opis:

07-09 Finding Mean

more » « less
Video Language:
English
Team:
Udacity
Projekt:
ud617 - Intro to Hadoop and Mapreduce
Duration:
01:15
Udacity Robot edited angielski subtitles for 07-09 Finding Mean
Udacity Robot edited angielski subtitles for 07-09 Finding Mean
Cogi-Admin edited angielski subtitles for 07-09 Finding Mean

English subtitles

Revisions Compare revisions