Using Fold method in dart

The fold method in dart is used for:
Reducing a collection to a single value by iteratively combining each element of the collection with an existing value

Uses [initialValue] as the initial value, then iterates through the elements and updates the value with each element using the [combine] function, as if by:

var value = initialValue;
for (E element in this) {
value = combine(value, element);
}
return value;

The fold method in dart just acts like the reduce method in javascript

Another example of the fold method in dart :
double get totalNetSpend {
return groupedTransactionData.fold(0.0, (sum, item) {
return sum + (item['amount'] as double);
});
}