Groovy function to generate Excel style column names from column a column index

ExcelColumn.groovy

@groovy.transform.Field
final def alphabet = ('A'..'Z')

def column(n) {
    n = n as Integer
    return (n < alphabet.size()) ?
                alphabet[n] :                           //first 'digit' is 1-based
                column((n / 26) - 1) + column(n % 26)   //0-based from now on, so reduce 1
}

assert column(  0) == 'A'
assert column(  1) == 'B'
assert column(  9) == 'J'
assert column( 25) == 'Z'
assert column( 26) == 'AA'
assert column( 27) == 'AB'
assert column( 28) == 'AC'
assert column( 35) == 'AJ'
assert column( 51) == 'AZ'
assert column( 52) == 'BA'
assert column(702) == 'AAA'

def ABBA = 0
[1, 2, 2, 0].reverse().eachWithIndex { e, i -> ABBA += e * 26**i }

assert column(ABBA) == 'ABBA'