fancyCollate.groovy

def numbers = 1..6

def max_splits = 7

count = numbers.size()
overflow = count % max_splits
pergroup = count.intdiv(max_splits)

println "Count: " + count + ", overflow: " + overflow + ", pergroup: " + pergroup

source_idx = 0
result = []

splits = Math.min(max_splits, count)

0.upto( splits-1 ) {
    if (it < overflow) {
        slice_size = pergroup + 1
    } else {
        slice_size = pergroup
    }
    
    result += [numbers[source_idx .. (source_idx + slice_size - 1)]]
    source_idx += slice_size
}

println "Result: " + result