Groovy Weekend – Collections: Splitting or Collating a List

I’ve been working with Groovy for some time now and I think it’s one of the best languages for the JVM.

To show my love for this language I dedicate this weekend to showcase some of the enhancements Groovy has made to working with Lists, Maps and Collections. Some small tidbits – just for fun every few hours.

I’ll call it the Groovy Weekend Collections Showcase Reel!…ahem. In this first installment we’ll start with…

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collate

collate() is a method on any Iterable to split or partition its elements into a sub-list of a certain size.

 
def names = ["Lassy", 
             "Buttercup", 
             "Carmella", 
             "Moo-moo", 
             "Cinnamon"]

// collate into batches of 3
def collated = names.collate 3
assert collated ==  
    [['Lassy', 'Buttercup', 'Carmella'], 
     ['Moo-moo', 'Cinnamon']]

You can even pass a 2nd parameter as the number of elements to step through for each sub-list.

collated = names.collate 3, 1
assert collated == [['Lassy', 'Buttercup', 'Carmella'], 
                    ['Buttercup', 'Carmella', 'Moo-moo'], 
                    ['Carmella', 'Moo-moo', 'Cinnamon'], 
                    ['Moo-moo', 'Cinnamon'], 
                    ['Cinnamon']]

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There are many overloaded variants of colate. Check out Groovy’s GDK documentation.