I have searched a lot. But couldn't get what I am looking for.
I have a list with inner lists as its objects
final posts = [ ["My First Post, "myPostId"], ["My SecondPost, "myPostId2"]..... ];
So, I want to check if the list contains the word First.
It is working with 1D lists like
posts = ["My First Post", "My Second Post"];
posts.where((p)=>p.contain("First")....
//gives the correct result
But what's the way to get from the inner lists.
Actual Code
final suggestion = query.isEmpty?courseNameList:courseNameList
.where((test)=>test.contains(query.toLowerCase())).toList();
Thanks in advance!
Hello check this solution if it is ok:
final posts = [
["My First Post", "myPostId"],
["My SecondPost", "myPostId2"],
];
void main() {
List suggestions = List();
posts.forEach((postList){
if(postList[0].contains("First"))
suggestions.add(postList);
});
suggestions.forEach((sugg)=>print("Found ID: ${sugg[1]}"));
}
void main() {
final result = posts.any((e) => e.any((e) => e.contains('First')));
print(result);
}
final posts = [
["My First Post", "myPostId"],
["My SecondPost", "myPostId2"]
];
Related
I'm attempting to extract a value from list contained in a list of maps, but am
getting the following error: The operator '[]' isn't defined for the type 'Object'
From the following list, I'd like to access a value such as 'Pizza':
List<Map<String,Object>> questions = [
{
'question': 'What is your favorite food',
'answers': [
'Pizza',
'Tacos',
'Sushi',
],
},
];
When I try to print an answer within the list of answers, it doesn't work:
// Does not work
// The operator '[]' isn't defined for the type 'Object'
print(questions[0]['answers'][0]);
I'm able to save the answers list into a variable to of type list then print a specific list item:
// Works
List answerList = questions[0]['answers'];
print(answerList[0]);
Why doesn't the first way work, and how can I get this to work with one command?
Rather than returning an Object return a dynamic as it has an operator []
List<Map<String, dynamic>> questions = [
{
'question': 'What is your favorite food',
'answers': [
'Pizza',
'Tacos',
'Sushi',
],
},
];
I am using flutter/dart and I have run into following problem.
I have a list of map like this.
var questions = [
{
'questionText': 'What\'s your favorite color?',
'answer': ['Black', 'Red', 'Green', 'White']
},
{
'questionText': 'What\'s your favorite animal?',
'answer': ['Deer', 'Tiger', 'Lion', 'Bear']
},
{
'questionText': 'What\'s your favorite movie?',
'answer': ['Die Hard', 'Due Date', 'Deep Rising', 'Dead or Alive']
},
];
Now suppose I need to get the string Tiger from this list. How do I do that? Dart is seeing this as List<Map<String, Object>> questions
Maybe a more portable way with a function:
String getAnswer(int question, int answer) {
return (questions[question]['answer'] as List<String>)[answer];
}
// Get 'Tiger'
String a = getAnswer(1, 1);
You can convert object in list in following way and then use index to get any value.
var p = questions[1]['answer'] as List<String>;
print(p[1]);
I am trying to iterate through a map and create a new map value. The below is the input
def map = [[name: 'hello', email: ['on', 'off'] ], [ name: 'bye', email: ['abc', 'xyz']]]
I want the resulting data to be like:
[hello: ['on', 'off'], bye: ['abc', 'xyz']]
The code I have right now -
result = [:]
map.each { key ->
result[random] = key.email.each {random ->
"$random"
}
}
return result
The above code returns
[hello: [on, off], bye: [abc, xyz]]
As you can see from above, the quotes from on, off and abc, xyz have disappeared, which is causing problems for me when i am trying to do checks on the list value [on, off]
It should not matter. If you see the result in Groovy console, they are still String.
Below should be sufficient:
map.collectEntries {
[ it.name, it.email ]
}
If you still need the single quotes to create a GString instead of a String, then below tweak would be required:
map.collectEntries {
[ it.name, it.email.collect { "'$it'" } ]
}
I personally do not see any reasoning behind doing the later way. BTW, map is not a Map, it is a List, you can rename it to avoid unnecessary confusions.
You could convert it to a json object and then everything will have quotes
This does it. There should/may be a groovier way though.
def listOfMaps = [[name: 'hello', email: ['on', 'off'] ], [ name: 'bye', email: ['abc', 'xyz']]]
def result = [:]
listOfMaps.each { map ->
def list = map.collect { k, v ->
v
}
result[list[0]] = ["'${list[1][0]}'", "'${list[1][1]}'"]
}
println result
I have movie database with different fields. the Genre field contains a comma separated string like :
{genre: 'Action, Adventure, Sci-Fi'}
I know I can use regular expression to find the matches. I also tried:
{'genre': {'$in': genre}}
the problem is the running time. it take lot of time to return a query result. the database has about 300K documents and I have done normal indexing over 'genre' field.
Would say use Map-Reduce to create a separate collection that stores the genre as an array with values coming from the split comma separated string, which you can then run the Map-Reduce job and administer queries on the output collection.
For example, I've created some sample documents to the foo collection:
db.foo.insert([
{genre: 'Action, Adventure, Sci-Fi'},
{genre: 'Thriller, Romantic'},
{genre: 'Comedy, Action'}
])
The following map/reduce operation will then produce the collection from which you can apply performant queries:
map = function() {
var array = this.genre.split(/\s*,\s*/);
emit(this._id, array);
}
reduce = function(key, values) {
return values;
}
result = db.runCommand({
"mapreduce" : "foo",
"map" : map,
"reduce" : reduce,
"out" : "foo_result"
});
Querying would be straightforward, leveraging the queries with an multi-key index on the value field:
db.foo_result.createIndex({"value": 1});
var genre = ['Action', 'Adventure'];
db.foo_result.find({'value': {'$in': genre}})
Output:
/* 0 */
{
"_id" : ObjectId("55842af93cab061ff5c618ce"),
"value" : [
"Action",
"Adventure",
"Sci-Fi"
]
}
/* 1 */
{
"_id" : ObjectId("55842af93cab061ff5c618d0"),
"value" : [
"Comedy",
"Action"
]
}
Well you cannot really do this efficiently so I'm glad you used the tag "performance" on your question.
If you want to do this with the "comma separated" data in a string in place you need to do this:
Either with a regex in general if it suits:
db.collection.find({ "genre": { "$regex": "Sci-Fi" } })
But not really efficient.
Or by JavaScript evaluation via $where:
db.collection.find(function() {
return (
this.genre.split(",")
.map(function(el) {
return el.replace(/^\s+/,"")
})
.indexOf("Sci-Fi") != -1;
)
})
Not really efficient and probably equal to above.
Or better yet and something that can use an index, the separate to an array and use a basic query:
{
"genre": [ "Action", "Adventure", "Sci-Fi" ]
}
With an index:
db.collection.ensureIndex({ "genre": 1 })
Then query:
db.collection.find({ "genre": "Sci-Fi" })
Which is when you do it that way it's that simple. And really efficient.
You make the choice.
I want to create a map of members, but every membres have 3 propreties : first name, last name, and username. How can I create like a list of liste, but with a map.
So I want to have something like :
var membres= {['lastname': 'Bonneau',
'firstname': 'Pierre',
'username': 'mariobross'],
['lastname': 'Hamel',
'firstname': 'Alex',
'username': 'Queenlatifa'],
};
As you know, this code doesn't work. But it explain pretty well what I am trying to do.
I think you are confusing the two constructs here.
Read this introduction to the language: http://www.dartlang.org/docs/dart-up-and-running/ch02.html#lists
A list is a list of elements which can be denoted with the shorthand [...] syntax:
var list = [1, 2, "foo", 3, new Date.now(), 4];
Whereas a map can be denoted with the curly brace shorthand syntax:
var gifts = { // A map literal
// Keys Values
'first' : 'partridge',
'second' : 'turtledoves',
'fifth' : 'golden rings'
};
So, let's modify your code to work:
var members = [
{
'lastname': 'Bonneau',
'firstname': 'Pierre',
'username': 'mariobross'
},
{
'lastname': 'Hamel',
'firstname': 'Alex',
'username': 'Queenlatifa'
}
];
You can, for example, print the information like this:
members.forEach((e) {
print(e['firstname']);
});
If I understand your intent correctly, you want to have a list of maps. What you have is correct except you confused [ and {. The following works:
var membres = [
{'lastname': 'Bonneau',
'firstname': 'Pierre',
'username': 'mariobross'},
{'lastname': 'Hamel',
'firstname': 'Alex',
'username': 'Queenlatifa'}
];
As an example, to get a list of all usernames:
print(membres.map((v) => v['username']));
If you don't really need a Map, what about using a class to improve the structure of your code :
class Member {
String firstname;
String lastname;
String username;
Member(this.firstname, this.lastname, this.username);
}
main() {
final members = new List<Member>();
members.add(new Member('Pierre', 'Bonneau', 'mariobross'));
members.add(new Member('Alex', 'Hamel', 'Queenlatifa'));
// use members
}
You mean like this?
// FirstName => LastName => Value
var lookup = new Map<String, Map<String, String>>();
// get / set values like this
void setValue(String firstName, String lastName, String value) {
if (!lookUp.containsKey(firstName))
lookUp[firstName] = new Map<String, String>();
lookUp[firstName][lastName] = value;
}
String getValue(String firstName, String lastName) {
if (!lookUp.containsKey(firstName)) return "";
return lookUp[firstName][lastName];
}
First of all you need to create a map with value as list. Dont forget to initialize it
then if you want to fill it you first need to use built in function like putIfAbsent as in dart to add first object in list and then use update to add items in list. therefore you will need two arrays. First to put elements and then to add elements in list with same key. Also you can use try catch to identify if the key is present or not to do that in one loop
for (var item in days) {
var date_time = DateTime.parse(item["date"] + " 00:00:00");
_events[date_time] = _events.putIfAbsent(
date_time,
() => [
{
"title": item["title"],
"date": item["date"],
"time": reUse.get_time_am_pm_format(item["time"]),
"feature": item["feature"],
}
]);
}
for (var item in days) {
var date_time = DateTime.parse(item["date"] + " 00:00:00");
_events[date_time] = _events.update(date_time, (value) {
value.add({
"title": item["title"],
"date": item["date"],
"time": reUse.get_time_am_pm_format(item["time"]),
"feature": item["feature"],
});
return value;
});
}