Big Data Simplified

Introducing MapReduce | 79

4.3.1 Using a Single Reducer

Let us consider the same data set from the previous example. For instance, assume that it has

three splits, so we will have one mapper process running on each of these splits of data, thereby

we have a total of three mappers.

FIGURE 4.10 Mapper outputs from splits

M

M

M

Split

1A

BA

CB

CBADC

DCADC

Split 2

Split 3

Each mapper will generate key value pairs as its output. Note that these are coded by alphabets

here for ease of understanding. Each code represents a specic key, in this case, a member name.

Thus, if there are two A’s, then these are pairs which have the same key. For instance, code A ...