After reading a line from a file, I have the following String:
"[0, 1, 2, 3, 4]"
What is the best way to convert this String back to List<int>?
Just base on following steps:
remove the '[]'
splint to List of String
turn it to a int List
Sth like this:
List<int> list =
value.replaceAll('[', '').replaceAll(']', '')
.split(',')
.map<int>((e) {
return int.tryParse(e); //use tryParse if you are not confirm all content is int or require other handling can also apply it here
}).toList();
Update:
You can also do this with the json.decode() as #pskink suggested if you confirm all content is int type, but you may need to cast to int in order to get the List<int> as default it will returns List<dynamic> type.
eg.
List<int> list = json.decode(value).cast<int>();
You can convert String list to int list by another alternate method.
void main() {
List<String> stringList= ['1','2','3','4'];
List<int> intList = [];
stringList.map((e){
var intValue = int.tryParse(e);
intList.add(intValue!);
print(intList);
});
print(a);
}
Or by using for in loop
void main() {
List<String> stringList= ['1','2','3','4'];
List<int> intList = [];
for (var i in stringList){
int? value = int.tryParse(i);
intList.add(value!);
print(intList);
}
}
Related
I'm searching for create a dynamic form which contain DropDownButtons.
Before do that, I'm trying something on DartPad to know if it's possible to call a list with some Strings.
Below an example about what I want to do (maybe what I'm searching for is now possible) :
void main() {
List<Map<String, String>> listOf3AInitial = [{"name": "4A"},
{"name": "5A"}
];
String _listOf = "listOf";
String _year = "3A";
String _type = "Initial";
var listOfType = "$_listOf$_year$_type";
print(listOfType);
}
In this case it print "listOf3AInitial" and I want to print the List {"name": "4A"},{"name": "5A"}.
How it is possible to do that ?
Regards
You have to map a string of it's value to do so. For example
List<Map<String, String>> listOf3AInitial = [{"name": "4A"}, {"name": "5A"}];
Map<String, List<Map<String, String>>> list3AInitialMap = {
"listOf3AInitial" : listOf3AInitial,
};
Now you can get a value from this map like
String _listOf = "listOf";
String _year = "3A";
String _type = "Initial";
var listOfType = "$_listOf$_year$_type";
print(list3AInitialMap[listOfType]);
Your var listOfType returns a String. Unfortunately, you cannot use/convert String as a variable name.
In this case, you may want to use a map:
void main() {
List<Map<String, String>> listOf3AInitial = [{"name": "4A"},{"name": "5A"}];
List<Map<String, String>> listOf3BInitial = [{"name": "4B"},{"name": "5B"}];
String _listOf = "listOf";
String _yearA = "3A"; //A
String _yearB = "3B"; //B
String _type = "Initial";
//Reference your lists in a map
Map<String, dynamic> myLists = {
"listOf3AInitial": listOf3AInitial,
"listOf3BInitial": listOf3BInitial
};
//This returns your listOf3AInitial
var listOfType = myLists["$_listOf$_yearA$_type"];
print(listOfType);
//You may also access it directly
print(myLists["$_listOf$_yearB$_type"]);
}
I was having an error like List<dynamic> is not a subtype of List<double> but here the problem is here List<double> is determined on runtime, I am doing something like this:-
extension Ext<T> on List<T> {
List<T> deepClone() {
List<T> res = [];
for (var value in this) {
if (value is List) {
res.add(value.deepClone() as T); //List<dynamic> is not the subtype of List<double>
} else {
res.add(value);
}
}
return res;
}
}
Now for example, if we call this method like this:-
List<List<double>> values = [[3, 4], [4, 1, 2]];
List<List<double>> cloneValues = values.deepClone(); //gives an error List<dynamic> is not the subtype of List<double>
List<List<List<String>>> strValues = [[["hello"], ["world", "hi"]], [["cat"]]];
List<List<List<String>>> clonedStrValues = strValues.deepClone() //gives and error List<dynamic> is not the subtype of List<String>
I researched a lot and found I cannot cast it on runtime, and the problem here is I need this function for different types of lists, so I cannot create a different function for each type either, can anyone help me?
The problem is that deepClone is not itself a generic function, which means that it can't recursively return different types - it can only return the type defined on the extension.
Therefore, instead of making the extension generic, make deepClone generic:
extension on List {
List<T> deepClone<T>() {
List<T> res = [];
for (var value in this) {
if (value is List) {
res.add(value.deepClone() as T);
} else {
res.add(value);
}
}
return res;
}
}
Also, it was probably just a typo, but in the code you posted, you iterated over res in your for loop, which of course will always be empty, since it was just created ;). Instead, the for loop should iterate over this.
i'm new in flutter and need to help:
I have already got
final List<Genres> genres = [{1,"comedy"}, {2,"drama"},{3,"horror"}]
from api.
class Genres {
final int id;
final String value;
Genres({this.id,this.value});
}
In another method I get genres.id.(2) How can I convert it to genres.value ("drama")?
Getting a Genre from an id is inconvenient when your data structure is a List. You have no choice but to iterate over the list and compare the id value to the id of each element in the list:
final id = 2;
final genre = genres.firstWhere((g) => g.id == id, orElse: () => null);
The problem with this code is that it's slow and there could be multiple matches (where the duplicates after the first found would be ignored).
A better approach would be to convert your list to a Map when you first create it. Afterwards, you can simply use an indexer to get a Genre for an ID quickly and safely.
final genresMap = Map.fromIterable(genres, (item) => item.id, (item) => item);
// later...
final id = 2;
final genre = genresMap[id];
This way, there is guaranteed to not be any duplicates, and if an ID doesn't exist then the indexer will simply return null.
you could iterate over the json result of the api and map them to the Gener class like so,
void fn(id) {
final gener = geners.firstWhere((gener) => gener['id'] == id);
// now you have access to your gener
}
You can find the item inside the List<Genres> like this
Genres element = list.firstWhere((element) => element.id == 2); // 2 being the id you give in the question as an exaple. You should make it dynamic
print(element.value);
I am a beginner in flutter how do i convert list of string into int. Below is the example code
var data="18:00";
List<String> dataList = data.split(':');
print(datalist[0]);
print(datalist[1]);
Output will be 18 and 00 under 18, so how do i get this 18 and 00 in int type.
You can convert your list of String into a list of int by mapping through each element and parsing to an int.
List<int> dataListAsInt = dataList.map((data) => int.parse(data)).toList();
Just parse your data with int.parse(//your data)
var data="18:00";
List<String> dataList = data.split(':');
print(int.parse(dataList[0]));
print(int.parse(dataList[1]));
you can do this like:
var data="18:00";
List<String> dataList = data.split(':');
for(String s in datalist){
int a=int.parse(s);
print(a);
}
hope this will help you
How to convert string to int
int.parse(data.split(':')) // this is how
Did several google searches, nothing helpful came up. Been banging my head against some errors when trying to do something that should be pretty simple. Convert a map such as {2019-07-26 15:08:42.889861: 150, 2019-07-27 10:26:28.909330: 182} into a list of objects with the format:
class Weight {
final DateTime date;
final double weight;
bool selected = false;
Weight(this.date, this.weight);
}
I've tried things like: List<Weight> weightData = weights.map((key, value) => Weight(key, value));
There's no toList() method for maps, apparently. So far I'm not loving maps in dart. Nomenclature is confusing between the object type map and the map function. Makes troubleshooting on the internet excruciating.
Following on Richard Heap's comment above, I would:
List<Weight> weightData =
mapData.entries.map( (entry) => Weight(entry.key, entry.value)).toList();
Don't forget to call toList, as Dart's map returns a kind of Iterable.
List<Weight> weightData = List();
weights.forEach((k,v) => weightData.add(Weight(k,v)));
Sometimes the typecast will fail and you can enforce it by doing:
List<Weight> weightData =
weightData.entries.map<Weight>( (entry) => Weight(entry.key, entry.value)).toList();
Example from my project where it wasn't working without typecast:
List<NetworkOption> networkOptions = response.data['data']['networks']
.map<NetworkOption>((x) => NetworkOption.fromJson(x))
.toList();
Use the entries property on the map object
This returns a List of type MapEntry<key,value>.
myMap.entries.map((entry) => "${entry.key} + ${entry.value}").toList();
You can also use a for collection to achieve the same.
var list = [for (var e in map.entries) FooClass(e.key, e.value)];
Details
Flutter 1.26.0-18.0.pre.106
Solution
/libs/extensions/map.dart
extension ListFromMap<Key, Element> on Map<Key, Element> {
List<T> toList<T>(
T Function(MapEntry<Key, Element> entry) getElement) =>
entries.map(getElement).toList();
}
Usage
import 'package:myApp/libs/extensions/map.dart';
final map = {'a': 1, 'b': 2};
print(map.toList((e) => e.value));
print(map.toList((e) => e.key));
You can do this:
List<Weight> weightData = (weights as List ?? []).map((key, value) => Weight(key,value)).toList()
or you can try:
List<Weight> weightData = List.from(weights.map((key, value) => Weight(key, value)))
If you need to convert Map values to a list, the simplest oneline code looks like this:
final list = map.values.toList();
Vidor answer is correct .any way this worked for me
List<String> list = new List();
userDetails.forEach((k, v) => list.add(userDetails[k].toString()));
its very simple just initialize a list of your custom object like this
List<CustomObject> list=[];
for (int i = 0; i < map.length; i++) {
CustomObject customObject= CustomObject(
date:map[i]['key'],
weight:map[i]['key']
);
list.add(CustomObject);
}
hope it works for you thanks
You simply don't need to. the values property is an Iterable<> of your objects. You can iterate over this or you can convert it to a list. For example,
// ignore_for_file: avoid_print
import 'package:flutter/material.dart';
import 'package:flutter_test/flutter_test.dart';
void main() {
testWidgets("convert Map to List of Objects", (tester) async {
final weight1 = Weight(const ValueKey("1"), DateTime.now(), 1);
final weight2 = Weight(const ValueKey("2"), DateTime.now(), 2);
final map = {weight1.key: weight1, weight2.key: weight2};
//You don't have to convert this to a list
//But you can if you want to
final list = map.values.toList();
list.forEach((w) => print("Key: ${w.key} Weight: ${w.weight} "));
});
}
class Weight {
final Key key;
final DateTime date;
final double weight;
bool selected = false;
Weight(this.key, this.date, this.weight);
}
Object Class
class ExampleObject {
String variable1;
String variable2;
ExampleObject({
required this.variable1,
required this.variable2,
});
Map<String, dynamic> toMap() {
return {
'variable1': this.variable1,
'variable2': this.variable2,
};
}
factory ExampleObject.fromMap(Map<String, dynamic> map) {
return ExampleObject(
variable1: map['variable1'] as String,
variable2: map['variable2'] as String,
);
}
}
Convert Map to Object List
List<ExampleObject> objectList = List<ExampleObject>.from(mapDataList.map((x) => ExampleObject.fromMap(x)));