method
retainWhere

void retainWhere(
bool test(E element)
)

Removes all objects from this list that fail to satisfy [test].

An object o satisfies [test] if test(o) is true.

List<String> numbers = ['one', 'two', 'three', 'four']; numbers.retainWhere((item) => item.length == 3); numbers.join(', '); // 'one, two'

Throws an [UnsupportedError] if this is a fixed-length list.