Summary - Collection methods

Combine map, where and fold to write a sales report.

Summary - Collection methods

In this group we learned five core collection methods: map transforms, where filters, fold/reduce reduces to one value, forEach does side effects, any/every query.

These methods work through Iterable and use lazy evaluation. They are chainable; for example list.where(...).map(...).fold(...) processes data in one flow.

Now let's do an exercise that uses three methods together: double numbers, filter evens and sum them.

Exercise Combine three methods

Chain on the list [1, 2, 3, 4, 5]: first double with map((n) => n * 2), then filter those greater than 5 with where((n) => n > 5), finally sum with fold(0, (acc, n) => acc + n). Print the result.

Show example solution

void main() {
  var numbers = [1, 2, 3, 4, 5];
  var result = numbers.map((n) => n * 2).where((n) => n > 5).fold(0, (acc, n) => acc + n);
  print(result);
}

Test yourself

Match methods to their purpose

map

Transform
where

Filter
fold

Reduce to one value
forEach

Side effect
Which method reduces to a single value?
- map
- forEach
- where
- fold
Show answer

fold — fold reduces a collection to a single value.

Next lesson: Model design

We Are Enhancing Your Experience

Cookie Preferences

Strictly Necessary Cookies

Analytical Cookies