December
02
A metaClass example of getting a random arraylist element
Yeah, yeah, OK, I can't name blog post titles very creatively :)
This is simply a repost of a blog post I did a few months ago, but I'm not sure many people here have read my other more generalized blog,
so I'll repost the Groovyish content here now and then.
Someone recently asked how to get a random element from an array. In PHP it’s pretty straightforward - array_rand($x) - but there’s not (AFAICT) a built-in way in Groovy to do this. So I wrote a little something which should hopefully demonstrate the power of the metaClass stuff to boot.
ArrayList.metaClass.getRand = { number ->
if(number==0) {
return delegate[new Random().nextInt(delegate.size)]
} else {
def tempList = []
def counter = 0
while(counter>number) {
tempList.add(delegate[new Random().nextInt(delegate.size)])
counter
}
return tempList
}
}
def names = ['mike','matt','mark','lesley','jean','ron','jeff','martine']
println names.getRand()
println names.getRand(5)
The first call to getRand() on the names list will just return one name from the list. The second will return 5 random entries (and some could theoretically be repeated). I’ve added this getRand() method to the base ArrayList class at runtime, even though it’s likely declared ‘final’ in Java’s base libraries. This is one of the core powers of Groovy, and is pretty slick, imo.
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Great minds think alike ;). Here is a class I use as a Category or Mixin for Groovy Lists:
class RandomListUtils {
static def r = new Random()
static def rand(List self) {
self[r.nextInt(self.size())]
}
static def rand(List self, count) {
def newList = self.collect { it }
def result = []
count.times {
def randItem = newList.rand()
result
Note - this blog thing takes < div > tags and such - I do < div style='background-color:#ccc'> around code blocks.
Yeah, my comment was actually cut off somewhere within the code. :(
great information dude, definitely something that is really useful, now I can complete some projects, with this in my hands I have the chance to do something interesting.
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I haven’t checked in here for a while since I thought it was getting boring, but the last few posts are good quality so I guess I’ll add you back to my daily bloglist. You deserve it friend :)
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