In this blog-post, we would visualize how MapReduce Algorithms operates to perform a Word Count on a Text Input:

First of all, for all programmers out there, Here is the code (Javascript):

[sourcecode language=”javascript”]
var map = function (key, value, context) {
var words = value.split(/[^a-zA-Z]/);
for (var i = 0; i < words.length; i++) {
if (words[i] !== "") {
context.write(words[i].toLowerCase(), 1);
}
}
};
var reduce = function (key, values, context) {
var sum = 0;
while (values.hasNext()) {
sum += parseInt(values.next());
}
context.write(key, sum);
};
[/sourcecode]

Courtesy: Microsoft Hadoop on Azure Samples

Now, let’s visualize this using an example.

Suppose the Text is “Hadoop on Azure sample Hadoop is on Windows Azure Hadoop is on Windows server” – Then this is how you can think of what happens to your input when it is processed first by Map function and then by Reduce function:

Conclusion:

In this blog post, we visualized how MapReduce Algorithm operates for a WordCount Example.

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