Basic operations on integer Lists - flutter

Question

I have a list of integers:
var times = [
1573613134,
1573623934,
1573631134,
1573659934,
1573746334,
1573731934,
1573764334,
1573789534,
1573847134,
1573933534,
1573893934,
1573980334,
1574153134,
1574178334
];
I would like to see if the values in this list are smaller than a specified integer.
var staticTime = [1573764334];
The easy, but time costly solution would be to use a for loop and compare every value within the list to staticTime.
Does Dart contain a built-in method to run basic inequality operations on a list of values?

Answer 1

Have you tried different methods to compare their speeds? The answer will probably surprise you. Take this quick benchmark, for example:
final values = <some list of numbers with values ranging from 0 to 1000000>;
void withForLoop() {
final start = DateTime.now();
final results = <int>[];
for (int i = 0; i < values.length; i++) {
if (values[i] < 500000) {
results.add(i);
}
}
final end = DateTime.now();
print('withForLoop method duration: ${end.difference(start)}');
}
void withForEachLoop() {
final start = DateTime.now();
final results = <int>[];
for (int v in values) {
if (v < 500000) {
results.add(v);
}
}
final end = DateTime.now();
print('withForEachLoop method duration: ${end.difference(start)}');
}
void withWhere() {
final start = DateTime.now();
final results = values.where((i) => i < 500000).toList();
final end = DateTime.now();
print('withWhere method duration: ${end.difference(start)}');
}
Running this script with value having a length of 1,000,000 resulted in these times on my computer:
withForLoop method duration: 0:00:00.125000
withForEachLoop method duration: 0:00:00.129000
withWhere method duration: 0:00:00.470000
From this, several things can be deduced:
The regular for loop completed the fastest.
The iterator-based "for-each" loop was only slightly slower than the for loop. (3.2% slower)
The generator-based where method was by far the slowest. (276% slower)
All three completed remarkably fast given the sample size, particularly considering a good chunk of the execution time was likely due to the resizing and reallocation of the result list due to the add call (the where method doesn't do this explicitly in the code shown, but it does happen internally).
The generator methods (e.g. map, where, reduce, etc.) are good because of their convenience, not because of their speed. In terms of raw performance, the bog-standard for loop will almost always be the fastest (ignoring some fairly technical tricks possible in some low-level languages, most of which cannot be done in Dart). That being said, it took a list of a million elements or more for any of the attempts to take any appreciable amount of time, and chances are any application you make in Dart isn't going to deal with data sets anywhere close to that big. For data sets of a more reasonable size, any of the above attempts will likely be more than fast enough for your purposes.
If you learned anything from this answer, hopefully it was these two things:
Don't prematurely criticize the performance of certain patterns until you've benchmarked them yourself. (More often than not, your assumptions may be wrong.)
Don't worry about the performance of things that are inherently insanely fast. (Other parts of your program will bottleneck long before this does.)
(If you want to try the above code for yourself, try it out in DartPad.)

Answer 2

There is the built-in every() function.
var allSmaller = times.every((time) => time > staticTime);

Answer 3

If you want to know whether there is any value smaller than staticTime then use:
bool hasAnySmaller = times.any((time)=> time<staticTime);
If you want the list of integers smaller than the staticTime then use:
List<int> allSmaller = times.where((time)=>time<staticTime).toList();