A Groovy Alternative To Java 8 Streams and Collectors

Posted By: Todd Sharp on 3/22/2017 4:19 GMT

Tagged: Groovy, Java

I recently read this article over at DZone about using Java 8 Streams and Collectors to manipulate and perform calculations on a list of integers. I don't intend to start an argument over which language is better, but my immediate thought was that it would make a good blog post to show how one might perform these tasks in Groovy. Collections in Groovy have long been a shining example of how Groovy enhances Java with convenience methods for common tasks. Here's a recreation of all the examples in the DZone post to show you how easy Groovy makes them:

Let's throw together a List of 100 random integers:

	Random random = new Random()
	List numbers = (0..100).collect { Math.abs(random.nextInt()) % 100 + 1 }
	println 'Random list of 100 integers: ' + numbers

view raw streams-1.groovy hosted with ❤ by GitHub

Determining the sum and average is quite simple:

	println 'Computed sum of integers: ' + numbers.sum()
	println 'Computed average of integers: ' + numbers.sum() / numbers.size()

view raw streams-2.groovy hosted with ❤ by GitHub

Though, average isn't a built in method. So, let's add it using metaprogramming instead:

	List.metaClass.average = {
	return delegate.size() ? delegate.sum() / delegate.size() : 0
	}
	println 'Average using metaClass method: ' + numbers.average()

view raw streams-3.groovy hosted with ❤ by GitHub

What about min/max?

	println 'Minimum number: ' + numbers.min()
	println 'Maximum number: ' + numbers.max()

view raw streams-4.groovy hosted with ❤ by GitHub

There's no built in method to the DZone summarizingInt() example, but we can do either:

	println 'Summary: ' + [
	count : numbers.size(),
	sum : numbers.sum(),
	min : numbers.min(),
	average: numbers.average(),
	max : numbers.max(),
	]

view raw streams-5.groovy hosted with ❤ by GitHub

Or, again, add a method via metaprogramming:

	List.metaClass.summarizingInt = {
	return [
	count : delegate.size(),
	sum : delegate.sum() ?: 0,
	min : delegate.min() ?: 0,
	average: delegate.average(),
	max : delegate.max() ?: 0,
	]
	}

	println 'Summary using metaClass: ' + numbers.summarizingInt()

	def x = []
	println 'Summary using metaClass on empty list: ' + x.summarizingInt()
	// prints [count:0, sum:0, min:0, average:0, max:0]

view raw streams-6.groovy hosted with ❤ by GitHub

Partitioning a list? No problem in Groovy, just use groupBy:

	println 'Partitioning a List: ' + numbers.groupBy { it > 50 ? true : false }
	// prints: [false:[16, 35, 34...], true:[96, 54, 58...]]

view raw streams-7.groovy hosted with ❤ by GitHub

Here's the full example in case you'd like to run them all yourself:

	Random random = new Random()
	List numbers = (0..100).collect { Math.abs(random.nextInt()) % 100 + 1 }
	println 'Random list of 100 integers: ' + numbers

	println 'Computed sum of integers: ' + numbers.sum()
	println 'Computed average of integers: ' + numbers.sum() / numbers.size()

	List.metaClass.average = {
	return delegate.size() ? delegate.sum() / delegate.size() : 0
	}
	println 'Average using metaClass method: ' + numbers.average()

	println 'Minimum number: ' + numbers.min()
	println 'Maximum number: ' + numbers.max()

	println 'Summary: ' + [
	count : numbers.size(),
	sum : numbers.sum(),
	min : numbers.min(),
	average: numbers.average(),
	max : numbers.max(),
	]

	List.metaClass.summarizingInt = {
	return [
	count : delegate.size(),
	sum : delegate.sum() ?: 0,
	min : delegate.min() ?: 0,
	average: delegate.average(),
	max : delegate.max() ?: 0,
	]
	}

	println 'Summary using metaClass: ' + numbers.summarizingInt()

	def x = []
	println 'Summary using metaClass on empty list: ' + x.summarizingInt()
	// prints [count:0, sum:0, min:0, average:0, max:0]

	println 'Partitioning a List: ' + numbers.groupBy { it > 50 ? true : false }
	// prints: [false:[16, 35, 34...], true:[96, 54, 58...]]

view raw streams-all.groovy hosted with ❤ by GitHub

Image by romaneau from Pixabay

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A Groovy Alternative To Java 8 Streams and Collectors

Posted By: Todd Sharp on 3/22/2017 4:19 GMT

Tagged: Groovy, Java

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