How to access map keys through index? Dart - dart

dartques = {'Color':[], 'Fruits':[], 'Hobbies':[]};
How to access the values using index in map?
I need to access only key or value using index.
Just like we do in list
=>list[1]

you can get it like this
var element = dartques.values.elementAt(0);
also for Dart 2.7+ you can write extension function
extension GetByKeyIndex on Map {
elementAt(int index) => this.values.elementAt(index);
}
var element = dartques.elementAt(1);

For accessing the values by index, there are two approaches:
Get Key by index and value using the key:
final key = dartques.keys.elementAt(index);
final value = dartques[key];
Get value by index:
final value = dartques.values.elementAt(index);
You may choose the approach based on how and what data are stored on the map.
For example if your map consists of data in which there are duplicate values, I would recommend using the first approach as it allows you to get key at the index first and then the value so you can know if the value is the wanted one or not.
But if you do not care about duplication and only want to find a value based on Index then you should use the second approach, as it gives you the value directly.
Note: As per this Answer By Genchi Genbutsu, you can also use Extension methods for your convenience.
Important:
Since the default implementation for Map in dart is LinkedHashmap you are in great luck. Otherwise Generic Map is known for not maintaining order in many programming languages.
If this was asked for any other language for which the default was HashMap, it might have been impossible to answer.

You can convert it to two lists using keys and values methods:
var ques = {'Color':['a'], 'Fruits':['b'], 'Hobbies':['c']};
List keys = ques.keys.toList();
List values = ques.values.toList();
print (keys);
print (values);
The output:
[Color, Fruits, Hobbies]
[[a], [b], [c]]
So you can access it normally by using keys[0], for example.

Related

Get default value from Erlang record definition?

Is there an easy way to get a default value from an Erlang record definition? Suppose I have something like this:
-record(specialfield, {
raw = <<"default">> :: string()
}).
I would like to have some way to retrieve the default value of the raw field. Something like this would be very simple:
#specialfield.raw % => <<"default">>
This is not possible. I would need to instantiate a record in order to get the default value:
Afield = #specialfield{}
DefaultValue = Afeild#specialfield.raw
DefaultValue % => <<"default">>
Is there an easier way of doing this? I seems like there should be some way to retrieve the default value without having to create an instance of the record.
How about:
raw_default() -> <<"default">>.
-record(specialfield, { raw = raw_default() }).
And now you have a function with the default in it. This will be extremely fast since it is a function call to a constant value. If this is also too slow, enable inlining.
Constructing an empty record and accessing one field can be done on one line:
(#specialfield{})#specialfield.raw.
Take a look at erlang - records, search section "11.8".
There's not much special about records - they're just a tuple at runtime. So to get the field raw from the tuple of default values that is the internal representation of #specialfield{} you would use:
element(#specialfield.raw, #specialfield{}).
In this case, #specialfield.raw is the index of the value for raw in the #specialfield tuple. When you pass in specialfield that resolves to a tuple in the form {specialfield, <<"default">>}.

Any reason for URLEncodedUtils.parse return List< NameValuePair >

https://hc.apache.org/httpcomponents-client-4.3.x/httpclient/apidocs/org/apache/http/client/utils/URLEncodedUtils.html#parse(java.net.URI,%20java.lang.String)
why not return Map< String, List< String > >
if it returns Map, user can easily query by key to get whatever they want.
otherwise user should iterator the whole list to find what they want.
Thanks
Because this is a list. If you read carefully the explanation, says:
Returns a list of NameValuePairs as built from the URI's query portion. For example, a URI of http://example.org/path/to/file?a=1&b=2&c=3 would return a list of three NameValuePairs, one for a=1, one for b=2, and one for c=3.
That means that you cannot use a list to acces by value, because these type of data structures aren't designed for that. They doesn't have any "key" to use.
In this website, Jon Skeet wrote a very clear answer about you cannot use a shortcut to acces a List<NameValuePair> value using a name or a key or for similar structures.
Here you can check the post: Get ArrayList<NameValuePair> value by name
Inside of the same post, you'll see different options to solve your problem. (Or could guide to you to find the solution)

passing collections as parameters with neo4j

I have been using parameters to query node indexes as such (using the rest api in java)-
final QueryResult<Map<String,Object>> result = engine.query("start nd=node:name_index(name={src}) return nd.age as age", MapUtil.map("src", "Susan");
However I haven't been able to get this to work for a collection of nodes/names. I have been trying something along the lines of-
final QueryResult<Map<String,Object>> result = engine.query("start nd=node:name_index(name={src}) return nd.age as age", MapUtil.map("src", Arrays.asList("Susan","Brian", "Ian"));
But it refuses to compile. I as wondering if there is something wrong in my syntax or that parameters are not designed to work in this context.
The name= syntax in the start is meant to do an index lookup on a property. It won't do an IN lookup. The way you can do this sort of lookup is like this (note it depends on Apache's StringUtils):
List<String> names = Arrays.asList("Susan","Brian", "Ian");
String luceneQuery = "name:("+StringUtils.join(names, ",")+")";
engine.query("start nd=node:name_index({luceneQuery}) return nd.age as age", MapUtil.map("luceneQuery", luceneQuery));
Just a note, this is the "legacy" index way of doing things. In 2.0 they've introduced label-based indexes, which work entirely differently.
Thanks a lot; though it would still only return a non empty answer when I added a space after the comma in line 2. I used-
String luceneQuery = "name:("+StringUtils.join(names, ", ")+")";
and it returned the age of one person. When I tried this:
String luceneQuery = "fs:(fs:"+ StringUtils.join(names, " OR fs:")+")";
it gave me all three ages. However, I am still unsure about whether this query will be able to leverage the usual advantages of parameters , i.e. will the engine be able to reuse the query and execution path the next time around (this time we may want to query for 4 names instead of 3)

Determine Data Type

I have this code in my controller:
def cols = grailsApplication.getDomainClass('com.archie.Build').persistentProperties.collect {it.name}
The code above will allow me to list all the property names I have in Build class. Now, I would like to include also the properties data type, ie. boolean, String etc...
Somewhat like the output is:
[floorType:String, floorWidth:Float, ......]
Maybe not exactly like that, or maybe similar, but as long as I can return their data type. Can someone help? Thank you.
Each entry in persistentProperties is a GrailsDomainClassProperty, and this provides access to the type of the property as a Class object:
def props = [:]
grailsApplication.getDomainClass('com.archie.Build'
).persistentProperties.each {
props[it.name] = it.type.name
}
Or just pass the persistentProperties array itself through to the GSP, then extract .name and .type there.
You may also wish to consider using constrainedProperties instead of/in addition to the persistentProperties. The constrainedProperties map lists only those properties that are mentioned in the domain class constraints block, but the iterator over this map is guaranteed to return the properties in the order they are listed in the constraints. This is how the default scaffolding operates, as I'm not aware of any way to control the order of the persistentProperties array.

How do I use hashset in actionscript

Right now I am using ArrayCollection. But I want to change that to Set as I want make sure do duplicate values come.
var addressList:ArrayCollection = new ArrayCollection();
One way is I can use Dictionary and store addresses as a key. And I can just use keys to iterate.
But I am looking for Java HashSet like implementation.
You want to download Polygonal Data Structures. The swc contains a HashSet. If you want Java-style template syntax for Flash, you should also check out Haxe.
The AS3 equivalent to HashMap or HashSet is the Dictionary class, and to a lesser extent, the Object class. Object keys are stored as strings, while with Dictionary the keys are objects. You can't have duplicate entries with either. Are you looking for a specific implementation other than that?

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