How to use map() for multiple lists? - list

Question

I want to get something like this:
[list1, list2].map( (var1, var2) => do something with var1;
do something with var2)
I tried:
List<int> counts = [1,2,3];
List<String> strings = ['','2',''];
print([counts, strings].map((list) => list[0].isEven; list[1].lenght))

Answer 1

IterableZip from package:collection should help.
https://pub.dartlang.org/documentation/collection/latest/collection/IterableZip-class.html
IterableZip([list1, list2]).map((values) {
doSomethingWith(values[0]);
doSomethingWith(values[1]);
});

Answer 2

It sounds like https://pub.dartlang.org/documentation/async/latest/async/StreamZip-class.html is what you want.
First convert list1 and list2 into their own individual streams, and then use StreamZip to combine both streams.
This for example will turn both values into a stream of strings containing both values:
StreamZip([list1, list2]).map((valuePair) => "${valuePair[0]}, ${valuePair[1]}"));

Answer 3

Sounds like you want the zip function which dart doesn't provide by default. A quick implementation would be something like this:
List<T3> zipList<T1, T2, T3>(List<T1> l1, List<T2> l2, T3 Function(T1, T2) zipper) {
if (l1.isEmpty) throw ArgumentError.value(l1, "l1", "input list cannot be empty");
if (l1.length != l2.length) throw ArgumentError("Two lists must have the same length");
var result = List<T3>(l1.length);
for(var i = 0; i < l1.length; i++) {
result.add(zipper(l1[i], l2[i]));
}
return result;
}
// here a quick example of how to use it.
class Bar {
final int i;
final String s;
Bar(this.i, this.s);
#override
String toString() => "Bar: $i - $s";
}
void testZipList() {
var list1 = [1,2,3];
var list2 = ["", "2", ""];
var bars = zipList(list1, list2, (l1, l2) => Bar(l1, l2));
bars.forEach(print);
}

Answer 4

In addition to the zipList provided in the accepted answer, here is a listIterable that may be useful if you have iterables that are not lists, yet.
Iterable<T3> zipIterable<T1, T2, T3>(Iterable<T1> l1, Iterable<T2> l2, T3 Function(T1, T2) zipper) sync* {
var i1 = l1.iterator;
var i2 = l2.iterator;
while(true) {
var fin1 = !i1.moveNext();
var fin2 = !i2.moveNext();
if (fin1 != fin2) {
throw ArgumentError("Two iterables must have the same length");
}
if (fin1) {
return;
}
yield zipper(i1.current, i2.current);
}
}