I have a nested JSON file, consisting of keys and values which are string only. But the structure of the JSON file is not fixed, so sometimes it could be nested 3 levels, sometimes only 2 levels.
I wonder how i could serialize this in strict mode?
"live" : {
"host" : "localhost",
"somevalue" : "nothing",
"anobject" : {
"one" : "two",
"three" : "four",
"five" : {
"six" : "seven"
}
}
}
If i would know the structure of the JSON, i simply would write my own class for it, but since the keys are not fixed, and also the nesting could be into several levels, i really wonder how i cut put such an object into a specific type.
Any help or hints appreciated
I think invariants will serve you well here. First off, it might be helpful to know that you can type a keyed tree strictly in Hack:
<?hh // strict
class KeyedTree<+Tk as arraykey, +T> {
public function __construct(
private Map<Tk, KeyedTree<Tk, T>> $descendants = Map{},
private ?T $v = null
) {}
}
(It must be a class because cyclic shape definitions are sadly not allowed)
I haven't tried it yet, but type_structures and Fred Emmott's TypeAssert look to also be of interest. If some part of your JSON blob is known to be fixed, then you could isolate the nested, uncertain part and build a tree out of it with invariants. In the limiting case where the whole blob is unknown, then you could excise the TypeAssert since there's no interesting fixed structure to assert:
use FredEmmott\TypeAssert\TypeAssert;
class JSONParser {
const type Blob = shape(
'live' => shape(
'host' => string, // fixed
'somevalue' => string, // fixed
'anobject' => KeyedTree<arraykey, mixed> // nested and uncertain
)
);
public static function parse_json(string $json_str): this::Blob {
$json = json_decode($json_str, true);
invariant(!array_key_exists('anobject', $json), 'JSON is not properly formatted.');
$json['anobject'] = self::DFS($json['anobject']);
// replace the uncertain array with a `KeyedTree`
return TypeAssert::matchesTypeStructure(
type_structure(self::class, 'Blob'),
$json
);
return $json;
}
public static function DFS(array<arraykey, mixed> $tree): KeyedTree<arraykey, mixed> {
$descendants = Map{};
foreach($tree as $k => $v) {
if(is_array($v))
$descendants[$k] = self::DFS($v);
else
$descendants[$k] = new KeyedTree(Map{}, $v); // leaf node
}
return new KeyedTree($descendants);
}
}
Down the road, you'll still have to supplement containsKey invariants on the KeyedTree, but that's the reality with unstructured data in Hack.
Related
I am trying to create a custom collector in order to count valid elements of a list. I have done it using one of the already provide collectors:
arr.stream()
.filter(e -> e.matches("[:;][~-]?[)D]"))
.map(e -> 1)
.reduce(0, Integer::sum);
but as a challenge for myself, I wanted to create my own custom collector in order to understand it better. And this is where I got stuck.
It is probably something trivial but I am learning this and can't figure a supplier, an accumulator, and a combiner. I guess I still don't understand something about them. For instance, I have a similar stream:
arr1.stream()
.filter(e -> e.matches("[:;][~-]?[)D]"))
.map(e -> 1)
.collect(temporary array, adding to array, reduce);
AFAIK supplier is a function without arguments, which returns something. I studied standard examples and it is usually a method reference for a new collection, e.g. ArrayList::new. I tried to use constant 0, e -> 0 because I want to return a scalar. I think it is wrong because it makes the stream returning 0. If using method reference for a temporary collection, Java complains about a mismatch of types of a supplier and returning object. I am also confused about using an accumulator if the final result is a number as a combiner would reduce all elements to a number, e.g. (a,b) -> a + b`.
I'm completely stumped.
Probably part of your problem is that you cannot obviously create an accumulator for an Integer type since it is immutable.
You start with this:
System.out.println(IntStream.of(1,2,3).reduce(0, Integer::sum));
You can extend to this:
System.out.println(IntStream.of(1,2,3).boxed()
.collect(Collectors.reducing(0, (i1,i2)->i1+i2)));
Or even this, which has an intermediate mapping function
System.out.println(IntStream.of(1,2,3).boxed()
.collect(Collectors.reducing(0, i->i*2, (i1,i2)->i1+i2)));
You can get this far with your own Collector
Collector<Integer, Integer, Integer> myctry = Collector.of(
()->0,
(i1,i2)->{
// what to do here?
},
(i1,i2)->{
return i1+i2;
}
);
The accumulator is A function that folds a value into a mutable result container with mutable being the keyword here.
So, make a mutable integer
public class MutableInteger {
private int value;
public MutableInteger(int value) {
this.value = value;
}
public void set(int value) {
this.value = value;
}
public int intValue() {
return value;
}
}
And now:
Collector<MutableInteger, MutableInteger, MutableInteger> myc = Collector.of(
()->new MutableInteger(0),
(i1,i2)->{
i1.set(i1.intValue()+i2.intValue());
},
(i1,i2)->{
i1.set(i1.intValue()+i2.intValue());
return i1;
}
);
And then:
System.out.println(IntStream.of(1,2,3)
.mapToObj(MutableInteger::new)
.collect(myc).intValue());
Reference:
Example of stream reduction with distinct combiner and accumulator
EDIT: The finisher just does whatever with the final result. If you don't set it on purpose then it is set by default to IDENTITY_FINISH which is Function.identity() which says just to return the final result as is.
EDIT: If you're really desperate:
Collector<int[], int[], int[]> mycai = Collector.of(
()->new int[1],
(i1,i2)->i1[0] += i2[0],
(i1,i2)->{i1[0] += i2[0]; return i1;}
);
System.out.println(IntStream.of(1,2,3)
.mapToObj(v->{
int[] i = new int[1];
i[0] = v;
return i;
})
.collect(mycai)[0]);
Hello I am new to dart and trying to find an item by property name in a list of list.
class Product{
String id;
String title;
Product(this.id,this.title);
}
void main(){
List<List<Product>> allProdcuts=[
//New Prodcuts
[
Product("1","Hammer"),
Product("3","Nails"),
Product("2","Screws"),
],
futureItems,
//Old Prodcuts
[
Product("4","Rock"),
Product("5","Paper"),
Product("6","Scissor"),
],
//Rare Items
[
Product("7","Plank"),
Product("8","Wires"),
Product("9","Box"),
],
];
print(allProdcuts.where((itemsList)=>itemsList.contains((product)=>product.title='Wires')));
//Returns ()
}
I have tried using for a single List:
List<Product> futureItems= [
Product("101","Galactic Hammer"),
Product("301","Galactic Nails"),
Product("201","Galactic Screws"),
];
print(newProduct.firstWhere((p)=>p.title=='Hammer'));
//Instance of 'Product'
Also tried this:
print(allProdcuts.map((itemList)=>itemList.firstWhere((p)=>p.title=='Nails')));
// Bad state: No elementError: Bad state: No element.
But there is an element with the title='Nails'.I don't understand what I am doing wrong.
You are calling itemList.firstWhere((p)=>p.title=='Nails') on each list, also the ones with no element with title "Nails". Since firstWhere throws if there is no matching value, it does that for two of your three lists. Also, in the example, itemsList.contains(...) does not take a callback, so you are just checking whether a function is in the list, which it isn't. You might want to use any for that, but it won't solve the problem here.
To do this efficiently, I'd probably create helper function:
Product findByTitle(List<List<Product>> allProducts, String title) {
for (var products in allProducts) {
for (var product in products) {
if (product.title == title) return product;
}
}
// Or return `null`.
throw ArgumentError.value(title, "title", "No element with that title");
}
The return in the middle allows you to skip out of the double iteration the moment you have a match, something which is harder to do with firstWhere/map/forEach etc.
One alternative solutions would be:
var product = allProducts.expand((l) => l.where((p) => p.title == title)).first;
which finds all the products with the given title and flattens them into a single iterable, then picks the first one (if there are any). Because iterables are lazy, it will actually stop at the first match.
There are many ways to solve this.
One example is to use the forEach() method:
allProdcuts.forEach(
(List<Product> l)=>l.forEach(
(Product p){
if (p.title=="Nails")
print(p.id);
}
)
);
The for each method receives a function and applies this function to every element on the list. If you have a lists of lists, you can do this twice to get a function applied to each element of the sub lists.
The above code prints 3, which is the desired result.
Another solution would be to flatten the list first, so you can have an easier search later.
print(allProdcuts.any((innerListOfProducts) =>
innerListOfProducts.any((product) => product.title == 'Wires')));
This code will return true if 'Wires' is in the inner list, and false otherwise.
I'm trying to parse a JSON data and assign it to a POJO in Grails.
I started with
obj.param=jsonRequest.jsonWrap.attrib.something.jsonParam
After some experimenting and refactoring, it looks like this now.
jsonRequest.jsonWrap.attrib.something.with {
obj.param1=jsonParam1
obj.param2=jsonParam2
//...
}
}
Now, can I avoid the repeated use of obj reference?
I'm imagining that your actual starting point is something like the following. On the JSON side:
import groovy.json.JsonSlurper
String jsonText = '''{
"jsonWrap":{
"attrib":{
"something":{
"jsonParam1": "value1",
"jsonParam2": "value2",
"jsonParam3": "value3",
"jsonParam4": "value4",
"jsonParam5": "value5"
}
}
}
}'''
def jsonRequest = new JsonSlurper().parseText(jsonText)
On the Groovy side:
class ObjectType {
def param1, param2, param3, param4, param5
}
def obj = new ObjectType()
Now, if I had any control over how either the JSON side or the Groovy side are defined then I would do my darnedest to ensure that the property names of the JSON "something" object are exactly the same as the property names in the Groovy "ObjectType" class. For example, like this:
class ObjectType {
def jsonParam1, jsonParam2, jsonParam3, jsonParam4, jsonParam5
}
Then, unmarshalling the "something" object into Groovy is as simple as this:
def obj = new ObjectType(jsonRequest.jsonWrap.attrib.something)
Only one reference to the JSON object. Only one reference to the Groovy object. And the former is used to instantiate the latter. And furthermore, notice that there is no need to reference the properties at all. That is, JSON objects from the slurper are instances of Map, so if the property names match up, you can use the default "Map constructor" syntax.
If, however, you do not control property naming in either set of objects, I would still recommend a different Map-based short-cut. First define a constant Map from one set of property names to the other, like so:
def map = [param1:"jsonParam1", param2:"jsonParam2", param3:"jsonParam3",
param4:"jsonParam4", param5:"jsonParam5"]
Then I would use something like this for the object unmarshalling:
def obj = new ObjectType().with { o ->
jsonRequest.jsonWrap.attrib.something.with { j ->
map.each { oParam, jParam -> o[oParam] = j[jParam] }
}
o
}
i don't think there is a trivial way to trick groovy into "use objectA, if getting is needed and objectB for setting". If obj above is a map or you can apply a map to this object, then you could produce a map in your with block and use this. If you have to have nested structures then more work is needed.
def jsonParam = new Expando([ p1: 'p1', p2: 'p2', p3: 'p3', ])
def obj = new Expando(
jsonParam.with{
[
param1: p1,
param3: p3,
] // `with` will return this map
})
assert obj.param1==jsonParam.p1
assert obj.param3==jsonParam.p3
I use expandos for simple code.
I am trying to use a HashMap of Lists of strings in Vala, but it seems the object lifecycle is biting me. Here is my current code:
public class MyClass : CodeVisitor {
GLib.HashTable<string, GLib.List<string>> generic_classes = new GLib.HashTable<string, GLib.List<string>> (str_hash, str_equal);
public override void visit_data_type(DataType d) {
string c = ...
string s = ...
if (! this.generic_classes.contains(c)) {
this.generic_classes.insert(c, new GLib.List<string>());
}
unowned GLib.List<string> l = this.generic_classes.lookup(c);
bool is_dup = false;
foreach(unowned string ss in l) {
if (s == ss) {
is_dup = true;
}
}
if ( ! is_dup) {
l.append(s);
}
}
Note that I am adding a string value into the list associated with a string key. If the list doesn't exist, I create it.
Lets say I run the code with the same values of c and s three times. Based some printf debugging, it seems that only one list is created, yet each time it is empty. I'd expect the list of have size 0, then 1, and then 1. Am I doing something wrong when it comes to the Vala memory management/reference counting?
GLib.List is the problem here. Most operations on GLib.List and GLib.SList return a modified pointer, but the value in the hash table isn't modified. It's a bit hard to explain why that is a problem, and why GLib works that way, without diving down into the C. You have a few choices here.
Use one of the containers in libgee which support multiple values with the same key, like Gee.MultiMap. If you're working on something in the Vala compiler (which I'm guessing you are, as you're subclassing CodeVisitor), this isn't an option because the internal copy of gee Vala ships with doesn't include MultiMap.
Replace the GLib.List instances in the hash table. Unfortunately this is likely going to mean copying the whole list every time, and even then getting the memory management right would be a bit tricky, so I would avoid it if I were you.
Use something other than GLib.List. This is the way I would go if I were you.
Edit: I recently added GLib.GenericSet to Vala as an alternative binding for GHashTable, so the best solution now would be to use GLib.HashTable<string, GLib.GenericSet<string>>, assuming you're okay with depending on vala >= 0.26.
If I were you, I would use GLib.HashTable<string, GLib.HashTable<unowned string, string>>:
private static int main (string[] args) {
GLib.HashTable<string, GLib.HashTable<unowned string, string>> generic_classes =
new GLib.HashTable<string, GLib.HashTable<unowned string, string>> (GLib.str_hash, GLib.str_equal);
for (int i = 0 ; i < 3 ; i++) {
string c = "foo";
string s = i.to_string ();
unowned GLib.HashTable<unowned string, string>? inner_set = generic_classes[c];
stdout.printf ("Inserting <%s, %s>, ", c, s);
if (inner_set == null) {
var v = new GLib.HashTable<unowned string, string> (GLib.str_hash, GLib.str_equal);
inner_set = v;
generic_classes.insert ((owned) c, (owned) v);
}
inner_set.insert (s, (owned) s);
stdout.printf ("container now holds:\n");
generic_classes.foreach ((k, v) => {
stdout.printf ("\t%s:\n", k);
v.foreach ((ik, iv) => {
stdout.printf ("\t\t%s\n", iv);
});
});
}
return 0;
}
It may seem hackish to have a hash table with the key and value having the same value, but this is actually a common pattern in C as well, and specifically supported by GLib's hash table implementation.
Moral of the story: don't use GLib.List or GLib.SList unless you really know what you're doing, and even then it's generally best to avoid them. TBH we probably would have marked them as deprecated in Vala long ago if it weren't for the fact that they're very common when working with C APIs.
Vala's new can be a little weird when used as a parameter. I would recommend assigning the new list to a temporary, adding it to the list, then letting it go out of scope.
I would also recommend using libgee. It has better handling of generics than GLib.List and GLib.HashTable.
The following code prints:
false
false
true
{{a: b}, {a: b}}
code
import "dart:json" as JSON;
main() {
print(JSON.parse('{ "a" : "b" }') == JSON.parse('{ "a" : "b" }'));
print({ "a" : "b" } == { "a" : "b" });
print({ "a" : "b" }.toString() == { "a" : "b" }.toString());
Set s = new Set();
s.add(JSON.parse('{ "a" : "b" }'));
s.add(JSON.parse('{ "a" : "b" }'));
print(s);
}
I am using json and parsing two equivalent objects, storing them in a Set, hoping they will not be duplicated. This is not the case and it seems to be because the first two lines (unexpectedly?) results in false. What is an efficient way to correctly compare two Map objects assuming each were the result of JSON.parse()?
The recommended way to compare JSON maps or lists, possibly nested, for equality is by using the Equality classes from the following package
import 'package:collection/collection.dart';
E.g.,
Function eq = const DeepCollectionEquality().equals;
var json1 = JSON.parse('{ "a" : 1, "b" : 2 }');
var json2 = JSON.parse('{ "b" : 2, "a" : 1 }');
print(eq(json1, json2)); // => true
For details see this answer which talks about some of the different equality classes: How can I compare Lists for equality in Dart?.
This is a difficult one, because JSON objects are just Lists and Maps of num, String, bool and Null. Testing Maps and Lists on equality is still an issue in Dart, see https://code.google.com/p/dart/issues/detail?id=2217
UPDATE
This answer is not valid anymore, see answer #Patrice_Chalin
This is actually pretty hard, as the == operator on Maps and Lists doesn't really compare keys/values/elements to each other.
Depending on your use case, you may have to write a utility method. I once wrote this quick and dirty function:
bool mapsEqual(Map m1, Map m2) {
Iterable k1 = m1.keys;
Iterable k2 = m2.keys;
// Compare m1 to m2
if(k1.length!=k2.length) return false;
for(dynamic o in k1) {
if(!k2.contains(o)) return false;
if(m1[o] is Map) {
if(!(m2[o] is Map)) return false;
if(!mapsEqual(m1[o], m2[o])) return false;
} else {
if(m1[o] != m2[o]) return false;
}
}
return true;
}
Please note that while it handles nested JSON objects, it will always return false as soon as nested lists are involved. If you want to use this approach, you may need to add code for handling this.
Another approach I once started was to write wrappers for Map and List (implementing Map/List to use it normally) and override operator==, then use JsonParser and JsonListener to parse JSON strings using those wrappers. As I abandoned that pretty soon, I don't have code for it and don't know if it really would have worked, but it could be worth a try.
The matcher library, used from unittest, will do this.