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December 16, 2010

Groovy Goodness: Determine Min and Max Entries in a Map

Since Groovy 1.7.6 we can use the min() and max() methods on a Map. We use a closure to define the condition for a minimum or maximum value. If we use two parameters in the closure we must do a classic comparison. We return a negative value if the first parameters is less than the second, zero if they are both equal, or a positive value if the first parameter is greater than the second parameter. If we use a single parameter we can return a value that is used as Comparable for determining the maximum or minimum entry in the Map.

def money = [cents: 5, dime: 2, quarter: 3]

// Determine max entry.
assert money.max { it.value }.value == 5
assert money.max { it.key }.key == 'quarter'  // Use String comparison for key.
assert money.max { a, b ->
    a.key.size() <=> b.key.size() 
}.key == 'quarter'  // Use Comparator and compare key size.

// Determine min entry.
assert money.min { it.value }.value == 2
assert money.min { it.key }.key == 'cents'  // Use String comparison for key.
assert money.min { a, b ->
    a.key.size() <=> b.key.size() 
}.key == 'dime'  // Use Comparator and compare key size.