I have a map that initially has empty lists as values. And a list with various data. What I want to do is to search the list for items similar to the map keys and add them as values.
This is my code:
void main() {
List list = [];
var maps= {
'A' : [],
'B' : [],
'C' : [],
};
List y = ['A','B','C','A','B','C'];
maps.forEach((key,values){
List temp =[];
for (var i in y){
if(key == i) {
list.add(i);
}
temp = list;
}
maps[key] = temp;
list.clear();
print(maps);
});
}
This is the result I get
{A: [], B: [], C: []}
And I need this result
{A: [A,A], B: [B,B], C: [C,C]}
Thank you very much for your help.
Your issue is that at no point are you directly manipulating the existing List with the matching key in your Map.
And you don't need the list or the temp variables.
var maps = {
'A': [],
'B': [],
'C': [],
};
List y = ['A', 'B', 'C', 'A', 'B', 'C'];
maps.forEach((key, value) {
for (String char in y) {
if(char == key) {
maps[key]!.add(char); // this is what adds the matching String from the list to the corresponding list in the map
}
}
});
log(maps.toString()); // {A: [A, A], B: [B, B], C: [C, C]}
Related
I have a list like this.
[{ a, 2 }, { b, 2 }, { c, 2 }, { d, 1 }, { e, 2 }, { f, 1 }, { g, 1 }, { h, 3 }]
I want toread this list. for example ı want to print a or print 2.
How can I do this?
This is essentially a list of maps or a list of lists. In both cases, you could simply iterate over the 'root' list and for the child, print the different values.
// list with some random maps and lists inside it
List<dynamic> myList = [{'a': 2}, ['b', 2], ...];
Now you can iterate it and, depending on the contents, print them:
for (var item in myList) {
print(item);
// depending on the type, print/process it
if (item is List) {
for (var nestedItem in item) {
... // print each nested item
}
} else if (item is Map) {
print(item.keys);
print(item.values);
print(item.entries);
}
}
Depending on your needs, you can tweak/combine the code above.
One List is a List<String>? and the other is a List<dynamic>
I'd prefer not to change these data types. I just want to check if the contents are the same.
If I have a List [1, 2, 3] and a List [1, 2, 3] the output of a bool should be true
If I have a List [1, 2, 3] and a List [1, 3, 2] the output of a bool should be true
If I have a List [1, 2, 4] and a List [1, 2, 3] the output of a bool should be false
I will sort in this case and check equal like
final e1 = [1, 2, 3]..sort();
final e2 = [1, 3, 2]..sort();
print(e1.equals(e2)); //true
void main() {
List<int> a = [1, 2, 3];
List<dynamic> b = [1, 3, 3];
bool checkSame(List<dynamic> a, List<dynamic> b) {
var same = true;
if (a.length != b.length) {
same = false;
} else {
a.forEach((element) {
if (element.toString() != b[a.indexOf(element)].toString()) {
same = false;
}
});
}
return same;
}
bool val = checkSame(a, b);
print(val);
}
I recommend to use collection package with 564 like on pub.dev. to compare lists/maps/sets
i found from here https://stackoverflow.com/a/63633370/12838877
To compare list of integer and list of dynamic
import 'package:collection/collection.dart';
List<int> a = [1,2,4,5,6];
List<dynamic> b = [1,2,4,5,6];
List<dynamic> c = [1,4,5,6,2];
bool isEqual = DeepCollectionEquality().equals(a,b);
bool isEqual2 = DeepCollectionEquality().equals(a,c);
print(isEqual); // result is true without any error
print (isEqual2); // result is false , since its not ordered
UPDATE
if you want to compare 2 list dynamic unordered you can use code below
final unOrderedList = DeepCollectionEquality.unordered().equals(a,c);
print(unOrderedList); // result true
since its dynamic list, its also can compare between list that contain int,null, string ,list , etc,
List<dynamic> d = [1,"abc",2, null, ["a"], 4];
List<dynamic> e = [1,"abc",2, null, ["a"], 4];
final compare2list = DeepCollectionEquality.unordered().equals(d,e);
print(compare2list); // result true
I'm trying to create a copy/clone of a "List<List<Map'>>".
So far I tried:
dataFTY2 = dataFTY.map((element)=>element).toList();
dataFTY2 = json.decode(json.encode(dataFTY));
dataFTY2 = List.from(dataFTY);
Nothing seems to work. Whenever I change the copy "dataFTY2", dataFTY changes as well. I need this to be a completely independent copy. Please help. I cant seem to figure this out, its driving me crazy.
More code added for reference.
List failureDetails = [];
List trackIDs = [];
List dateTime = [];
var dataFTY2 = dataFTY.map((element) => element.map((ele) => Map.from(ele)).toList()).toList();
// get historyData for each one and sort through "F"s and put them into the table in a row?
for (var x in dataFTY2[4]) {
trackIDs.add(x["track_id"]);
dateTime.add(x["datetime"]);
}
List failuresOnly = List.filled(trackIDs.length, {}, growable: true);
for (var i = 0; i < trackIDs.length; i++) {
await fetchTrackIDTestDetails(context, trackIDs[i], dateTime[i], false);
failureDetails.add(MyGlobals().getTestCodeDetailsData());
}
//filter out only "F"s
for (var p = 0; p < failureDetails.length; p++) {
for (var t in failureDetails[p][0]) {
if (t["Status"] == "F") {
//add it to list, if pass do nothing
failuresOnly[p] = t;
}
}
}
//combine with FTY failure data, don't use new screen use old screen and toggle when pressed, add column on right side
//dataFTY2 = MyGlobals().getFTYFailureMoreDetails();
for (var i = 0; i < dataFTY2[4].length; i++) {
dataFTY2[4][i]["TestCode"] = failuresOnly[i]["TestCode"];
dataFTY2[4][i]["Status"] = failuresOnly[i]["Status"];
dataFTY2[4][i]["TestValue"] = failuresOnly[i]["TestValue"];
dataFTY2[4][i]["Lo_Limit"] = failuresOnly[i]["Lo_Limit"];
dataFTY2[4][i]["Up_Limit"] = failuresOnly[i]["Up_Limit"];
dataFTY2[4][i]["ProcTime"] = failuresOnly[i]["ProcTime"];
}
You can use Map.from named constructor to clone the Map like this,
dataFTY2 = dataFTY.map((element) => element.map((ele) => Map.from(ele)).toList()).toList();
I find it more straightforward to use collection-for and the spread (...) operator:
void main() {
var original = [
[
{'foo': 1, 'bar': 2},
{'foo': 3, 'bar': 4},
]
];
// Create a new List...
var copy = [
for (var sublist in original)
// ... where each element is a new List...
[
for (var map in sublist)
// ... where each element of the sublist is a new Map that
// copies all entries from `map`.
{...map},
],
];
original[0][0]['foo'] = -1;
print(original); // Prints: [[{foo: -1, bar: 2}, {foo: 3, bar: 4}]]
print(copy); // Prints: [[{foo: 1, bar: 2}, {foo: 3, bar: 4}]]
}
How I can get the most popular number from a list in dart without using any third party libraries?
var list = [0, 1, 1, 2, 2, 2, 3, 3, 4]; // most popular number is 2
If there are two or more popular numbers then the output should be a List with both values. Example:
One popular number:
var list = [0, 1, 1, 2, 2, 2, 3, 3, 4];
// Output should be [2]
Two or more popular numbers:
var list = [0, 1, 1, 2, 2, 2, 3, 3, 3];
// Output should be [2, 3]
Thank you in advance for your help!
This works...you can optimize it
var list = [1, 1, 2, 2, 3, 4, 5];
list.sort();
var popularNumbers = [];
List<Map<dynamic, dynamic>> data = [];
var maxOccurrence = 0;
var i = 0;
while (i < list.length) {
var number = list[i];
var occurrence = 1;
for (int j = 0; j < list.length; j++) {
if (j == i) {
continue;
}
else if (number == list[j]) {
occurrence++;
}
}
list.removeWhere((it) => it == number);
data.add({number: occurrence});
if (maxOccurrence < occurrence) {
maxOccurrence = occurrence;
}
}
data.forEach((map) {
if (map[map.keys.toList()[0]] == maxOccurrence) {
popularNumbers.add(map.keys.toList()[0]);
}
});
print(popularNumbers);
try this to count each element in list:
var list = [0, 1, 1, 2, 2, 2, 3, 3, 4];
var popular = Map();
list.forEach((l) {
if(!popular.containsKey(l)) {
popular[l] = 1;
} else {
popular[l] +=1;
}
});
I guess I found the solution.
Let me explain it to you:
I had queried through your list and checked whether the keys of the map contains the element or not. If the map does not contain the element as the key then, it will create a key from the element and pass 1 as the value. If the map does contain the element as a key then it will simply increment the value.
Once the map is ready, I had sorted the map values and stored them in a List. From the sorted map values I had taken the last element from the list of sorted values because we had sorted it in ascending order so the most popular value will be at last.
At last, I had queried through the map and check whether the value of the particular key is equal to the popularValue or not. If it is then we are adding the current key and value to the mostPopularValues list.
If I got something wrong please let me know.
void main() {
List list = [0, 1, 1, 1, 2, 2, 2, 3, 3, 4];
List mostPopularValues = [];
var map = Map();
list.forEach((element) {
if (!map.containsKey(element)) {
map[element] = 1;
} else {
map[element] += 1;
}
});
print(map);
// o/p : {0: 1, 1: 3, 2: 3, 3: 2, 4: 1}
List sortedValues = map.values.toList()..sort();
print(sortedValues);
// o/p : [1, 1, 2, 3, 3]
int popularValue = sortedValues.last;
print(popularValue);
// o/p : 3
map.forEach((k, v) {
if (v == popularValue) {
mostPopularValues.add("$k occurs $v time in the list");
}
});
print(mostPopularValues);
// o/p : [1 occurs 3 time in the list, 2 occurs 3 time in the list]
}
Not sure if that's the best solution, but it works pretty well. Let me know if there are any doubts.
final list = [0, 1, 1, 2, 2, 2, 3, 3, 4];
// Count occurrences of each item
final folded = list.fold({}, (acc, curr) {
acc[curr] = (acc[curr] ?? 0) + 1;
return acc;
}) as Map<dynamic, dynamic>;
// Sort the keys (your values) by its occurrences
final sortedKeys = folded.keys
.toList()
..sort((a, b) => folded[b].compareTo(folded[a]));
print('Most popular value: ${sortedKeys.first}'); // 1
print('Second most popular value: ${sortedKeys[1]}'); // 2
I have solved this problem by defining an extension on Iterable:
extension MostPopularItemsExtension<E> on Iterable<E> {
/// Returns the most popular items, where all items in the returned
/// list have the same number of occurances. If [this] is empty, returns an
/// empty list
///
/// Examples:
/// `[1,2,3,2].mostPopularItems() == [2]`
/// `[1,1,2,2].mostPopularItems() == [1,2]`
Iterable<E> mostPopularItems() {
if (isEmpty) return [];
final itemsCounted = <E, int>{};
for (final e in this) {
if (itemsCounted.containsKey(e)) {
itemsCounted[e] = itemsCounted[e]! + 1;
} else {
itemsCounted[e] = 1;
}
}
final highestCount = (itemsCounted.values.toList()..sort()).last;
return itemsCounted.entries
.where((e) => e.value == highestCount)
.map((e) => e.key);
}
}
The basic idea is to count all occurrences of each item in a Map object, get the highest count from this map and then return all items that have that specific number of occurrences.
I have a non-primitive list which I would like to sort.
When I sort it, the UI thread is blocked and the app freezes for a few seconds.
I tried to avoid this by using dart's Isloate compute function but since the parameter sent to the compute function must be a primitive or a list/map of primitives (send method) it didn't work.
To conclude, is there any way to perform a list sort(non-primitive) without blocking the UI thread?
Edit: Clarification - I was trying to call a function through compute and I was passing a list of objects (which I got from a third party plugin) as an argument, those objects had a property of type Iterable and that caused everything to fail - make sure all the types are primitive or List/Map of primitives. With the answers I received and changing the type from Iterable to List it worked.
I'm not sure if I understood your question, but you can sort a list of non primitive elements like this:
final List<Element> elements = [
Element(id: 1),
Element(id: 7),
Element(id: 2),
Element(id: 0)
];
elements.sort((a, b) => a.compareTo(b));
// or
elements.sort((a, b) => a.id > b.id ? 1 : -1);
This would be a print(elements); output:
I/flutter ( 7351): [id: 0, id: 1, id: 2, id: 7]
And this would be the class Element
class Element {
final int id;
Element({this.id});
#override
String toString() => "id: $id";
int compareTo(Element other) => this.id > other.id ? 1 : -1;
}
Edit: To make this asynchronously, you could do this:
Future<List<Element>> asyncSort() async {
print("before sort: $elements");
elements = await compute(_sort, elements);
print("after sort: $elements");
return elements;
}
static List<Element> _sort(List<Element> list) {
list.sort((a, b) => a.compareTo(b));
return list;
}
print("before calling asyncSort(): $elements");
asyncSort();
print("after calling asyncSort(): $elements");
And this would be the output:
I/flutter ( 7351): before calling asyncSort(): [id: 1, id: 7, id: 2, id: 0]
I/flutter ( 7351): before sort: [id: 1, id: 7, id: 2, id: 0]
I/flutter ( 7351): after calling asyncSort(): [id: 1, id: 7, id: 2, id: 0]
I/flutter ( 7351): after sort: [id: 0, id: 1, id: 2, id: 7]
Edit2: If you want to send a compare function to compute, you could use a Map or a List of arguments with the list and the compare function and pass that instead of the list, because compute just takes one argument. Here is an example:
Future<List<Element>> asyncSort() async {
print("before sort: $elements");
Map args = {"list": elements, "compare": compare};
elements = await compute(_sortWith, args);
print("after sort: $elements");
return elements;
}
static List<Element> _sortWith(Map args) {
List<Element> list = args["list"];
Function(Element a, Element b) compare = args["compare"];
list.sort((a, b) => compare(a, b));
return list;
}
static int compare(Element a, Element b) {
return a.id > b.id ? 1 : -1;
}
This is how i use compute, just put all parameters to a list, then call it in a List of dynamic object:
image = await compute(getCropImage, [copyFaces, streamImg]);
imglib.Image getCropImage(List<dynamic> values) {
var face = values[0]; // copyFaces
var image = values[1]; // streamImg
}