How to flatten a List?

Question

How can I easily flatten a `List` in Dart? For example: ``` var a = [[1, 2, 3], ['a', 'b', 'c'], [true, false, true]]; var b = [1, 2, 3, 'a', 'b', 'c', true, false, true]; ``` How do I turn `a` into `b`, i.e. into a single `List` containing all those values?

Accepted Answer

The easiest way I know of is to use `Iterable.expand()` with an identity function. `expand()` takes each element of an Iterable, performs a function on it that returns an iterable (the "expand" part), and then concatenates the results. In other languages it may be known as flatMap.

So by using an identity function, expand will just concatenate the items. If you really want a List, then use `toList()`.

```
var a = [[1, 2, 3], ['a', 'b', 'c'], [true, false, true]];
var flat = a.expand((i) => i).toList();
```

How to flatten a List?

Solution

Problem