Composability and removing duplication

We have already seen an example of where we had a fair amount of duplication:

const Sums sumsWithFunctionalLoops(const vector<int>& numbers){
    Sums theTotals;
    vector<int> evenNumbers;
    copy_if(numbers.begin(), numbers.end(), back_inserter(evenNumbers), 
    isEven);
    theTotals.evenSum = accumulate(evenNumbers.begin(), 
    evenNumbers.end(), 0);
 
    vector<int> oddNumbers;
    copy_if(numbers.begin(), numbers.end(), back_inserter(oddNumbers), 
    isOdd);
    theTotals.oddSum= accumulate(oddNumbers.begin(), oddNumbers.end(), 
    0);
 
    theTotals.total = accumulate(numbers.begin(), numbers.end(), 0);
 
    return theTotals;
}

We managed to reduce it using functions, as shown in the following code:

template<class UnaryPredicate>
const vector<int> filter(const vector<int>& input, UnaryPredicate filterFunction...