Is there a way in Dart using the list map method to build a list containing two (or more) items for-CodePudding

In Python, this code realizes the objective:

intLst = [1, 2, 3]
f1 = lambda x: x
f2 = lambda x: x * 10
newLst = [f(x) for x in intLst for f in [f1, f2]]

print(newLst) # [1, 10, 2, 20, 3, 30]

but in Dart I was not able to do the same using an anonymous function passed to the map() List method.

CodePudding user response：

You can achieve the same thing using collection for, which allows you to do the same type of things you can do with a list comprehension in python.

void main() {
  List<int> intLst = [1, 2, 3];
  int Function(int) f1 = (x) => x;
  int Function(int) f2 = (x) => x * 10;
  List<int> newLst = [
    for (var x in intLst)
      for (var f in [f1, f2]) f(x),
  ];
  print(newLst); // [1, 10, 2, 20, 3, 30]
}

The alternative would be to use expand rather than map. expand is the same as what some other languages call flatMap.

void main() {
  List<int> intLst = [1, 2, 3];
  int Function(int) f1 = (x) => x;
  int Function(int) f2 = (x) => x * 10;
  List<int> newLst = intLst.expand((v) => [f1(v), f2(v)]).toList();
  print(newLst); // [1, 10, 2, 20, 3, 30]
}

CodePudding user response：

Here's another way to obtain the same result without using functions:

void main() {
  List<int> intList = [1, 2, 3];

  List<int> newList = [
    for (var x in intList) ...[x, x * 10, x * x],
  ];

  print(newList); // [1, 10, 1, 2, 20, 4, 3, 30, 9]
}