A Groovy Alternative To Java 8 Streams and Collectors
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: ' + numbersDetermining the sum and average is quite simple:
println 'Computed sum of integers: ' + numbers.sum()
println 'Computed average of integers: ' + numbers.sum() / numbers.size()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()What about min/max?\
println 'Minimum number: ' + numbers.min()
println 'Maximum number: ' + numbers.max()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(),
]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]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...]]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...]]