reverse json javascript - javascript

Is there an inexpensive way to reverse:
{
"10": "..."
"11": "...",
"12": "...",
"13": "...",
"14": "...",
}
so that I get:
{
"14": "...",
"13": "...",
"12": "..."
"11": "...",
"10": "...",
}
reverse() doesn't seem to work on json objects. The only way I can think of is to loop through all the elements and create an array. feels like there should be a better way.
Edit: thanks for all the help UPDATE:
What about let's say if each key has chronological data. When I use $.each on the object, it runs through the objects from top to bottom, I didn't realize that was unreliable.
Here's what I'm trying to do:
$.each(object, function (key, value) {
function foo (key, value);
});
I want to not run foo on all but the last 3 pairs, that is I only want to use the last 3 pairs. I figured if I can reverse them I can just run the first three and stop.
Is there any way I can just do the last 3? If the last 3 ordering is unreliable, is there a safer way to grab the last 3. The last 3 will have the largest numerical keys.
Thanks.
Edit 2:
I'm basically deciding finally to do the manipulations on the server side. I'm reorganizing my database so that the relevant subdocuments are now full on documents that could be queried with mongodb. Thanks.

Javascript associative arrays are unordered. You cannot depend on the properties being in any particular order.
From Mozilla Developer Network:
Although ECMAScript makes iteration
order of objects
implementation-dependent, it may
appear that all major browsers support
an iteration order based on the
earliest added property coming first
(at least for properties not on the
prototype). However, in the case of
Internet Explorer, when one uses
delete on a property, some confusing
behavior results, preventing other
browsers from using simple objects
like object literals as ordered
associative arrays. In Explorer, while
the property value is indeed set to
undefined, if one later adds back a
property with the same name, the
property will be iterated in its old
position--not at the end of the
iteration sequence as one might expect
after having deleted the property and
then added it back.
So if you want to simulate an ordered
associative array in a cross-browser
environment, you are forced to either
use two separate arrays (one for the
keys and the other for the values), or
build an array of single-property
objects, etc.

Use this on json objects arrays
jsonObjectArray.reverse();
$.each(jsonObjectArray, function(i, item) {
//do something with the item
});
Hope this helps

This might help. Get all the keys from the json objects into an array, which you can sort.
var a = { 1 : 'x', 3 : 'y', 2 : 'z' };
var keys = []
for (i in a) { keys.push(i); }
keys.sort();
then you can use reverse() and slice() to just iterate over the keys you need.
$.each(keys, function(idx, key) {
// do whatever with a[key]
});

Follow the json in reverse order,
for(json.length;i>=0;i--)
{
console.log(json.[i]);
}

Related

How to keep order from json.parse? [duplicate]

I have some data which I originally stored in a generic Javascript object, with the ID as a key:
{
"7": {"id":"7","name":"Hello"},
"3": {"id":"3","name":"World"},
...
}
However, I discovered that browsers do not guarantee a particular object order when looping through them, so in the above "3" would come before "7". I switched to using an array format like this:
[
{"id":"7","name":"Hello"},
{"id":"3","name":"World"},
...
]
Now, I can loop in the correct order but cannot do fast lookups, e.g. data["3"] without having to loop through the array.
Is there a good way to combine both approaches? I would rather avoid using a separate object for each format, because the object is pretty large (hundreds of elements).
I have run across this problem as well. A solution is to keep an ordered array of keys in addition to the original object.
var objects = {
"7": {"id":"7","name":"Hello"},
"3": {"id":"3","name":"World"},
...
}
var order = [ "3", "7", ... ];
Now if you want the second element you can do this lookup:
var second_object = objects[order[1]];
The ECMA standard does not say anything about the order of the elements in an object. And specifically Chrome reorders the keys when they look like numbers.
Example:
var example = {
"a": "a",
"b": "b",
"1": "1",
"2": "2"
};
if you print this in Chrome will get something like:
{
1: "1",
2: "2",
"a": "a",
"b": "b"
};
It's a little sour .. but life.
You could use the solution Andy linked as well, basically wrapping these two together in one object.
An alternative that I use a lot is a custom map function that allows you to specify the order in which the object is traversed. Typically you will do sorting when you're printing your data to the user so while you loop and create your table rows (for instance) your iterator will pass the rows in the order your sort function specifies. I thought it was a nice idea :)
The signature looks like:
function map(object, callback, sort_function);
Example usage:
map(object, function (row) {
table.add_row(row.header, row.value);
}, function (key1, key2) {
return object[key1] - object[key2];
});
Rather than coding your own, there are off-the-shelf libraries available to provide "as provided" JSON parsing or "consistently sorted" JSON printing for display.
You might well consider either of these:
The 'json-order' package offers parsing, formatting & pretty-printing with stable ordering. This is based on having ordered input.
The 'fast-json-stable-stringify' package offers deterministic formatting based on sorting.

Updating a Nested Array with MongoDB

I am trying to update a value in the nested array but can't get it to work.
My object is like this
{
"_id": {
"$oid": "1"
},
"array1": [
{
"_id": "12",
"array2": [
{
"_id": "123",
"answeredBy": [], // need to push "success"
},
{
"_id": "124",
"answeredBy": [],
}
],
}
]
}
I need to push a value to "answeredBy" array.
In the below example, I tried pushing "success" string to the "answeredBy" array of the "123 _id" object but it does not work.
callback = function(err,value){
if(err){
res.send(err);
}else{
res.send(value);
}
};
conditions = {
"_id": 1,
"array1._id": 12,
"array2._id": 123
};
updates = {
$push: {
"array2.$.answeredBy": "success"
}
};
options = {
upsert: true
};
Model.update(conditions, updates, options, callback);
I found this link, but its answer only says I should use object like structure instead of array's. This cannot be applied in my situation. I really need my object to be nested in arrays
It would be great if you can help me out here. I've been spending hours to figure this out.
Thank you in advance!
General Scope and Explanation
There are a few things wrong with what you are doing here. Firstly your query conditions. You are referring to several _id values where you should not need to, and at least one of which is not on the top level.
In order to get into a "nested" value and also presuming that _id value is unique and would not appear in any other document, you query form should be like this:
Model.update(
{ "array1.array2._id": "123" },
{ "$push": { "array1.0.array2.$.answeredBy": "success" } },
function(err,numAffected) {
// something with the result in here
}
);
Now that would actually work, but really it is only a fluke that it does as there are very good reasons why it should not work for you.
The important reading is in the official documentation for the positional $ operator under the subject of "Nested Arrays". What this says is:
The positional $ operator cannot be used for queries which traverse more than one array, such as queries that traverse arrays nested within other arrays, because the replacement for the $ placeholder is a single value
Specifically what that means is the element that will be matched and returned in the positional placeholder is the value of the index from the first matching array. This means in your case the matching index on the "top" level array.
So if you look at the query notation as shown, we have "hardcoded" the first ( or 0 index ) position in the top level array, and it just so happens that the matching element within "array2" is also the zero index entry.
To demonstrate this you can change the matching _id value to "124" and the result will $push an new entry onto the element with _id "123" as they are both in the zero index entry of "array1" and that is the value returned to the placeholder.
So that is the general problem with nesting arrays. You could remove one of the levels and you would still be able to $push to the correct element in your "top" array, but there would still be multiple levels.
Try to avoid nesting arrays as you will run into update problems as is shown.
The general case is to "flatten" the things you "think" are "levels" and actually make theses "attributes" on the final detail items. For example, the "flattened" form of the structure in the question should be something like:
{
"answers": [
{ "by": "success", "type2": "123", "type1": "12" }
]
}
Or even when accepting the inner array is $push only, and never updated:
{
"array": [
{ "type1": "12", "type2": "123", "answeredBy": ["success"] },
{ "type1": "12", "type2": "124", "answeredBy": [] }
]
}
Which both lend themselves to atomic updates within the scope of the positional $ operator
MongoDB 3.6 and Above
From MongoDB 3.6 there are new features available to work with nested arrays. This uses the positional filtered $[<identifier>] syntax in order to match the specific elements and apply different conditions through arrayFilters in the update statement:
Model.update(
{
"_id": 1,
"array1": {
"$elemMatch": {
"_id": "12","array2._id": "123"
}
}
},
{
"$push": { "array1.$[outer].array2.$[inner].answeredBy": "success" }
},
{
"arrayFilters": [{ "outer._id": "12" },{ "inner._id": "123" }]
}
)
The "arrayFilters" as passed to the options for .update() or even
.updateOne(), .updateMany(), .findOneAndUpdate() or .bulkWrite() method specifies the conditions to match on the identifier given in the update statement. Any elements that match the condition given will be updated.
Because the structure is "nested", we actually use "multiple filters" as is specified with an "array" of filter definitions as shown. The marked "identifier" is used in matching against the positional filtered $[<identifier>] syntax actually used in the update block of the statement. In this case inner and outer are the identifiers used for each condition as specified with the nested chain.
This new expansion makes the update of nested array content possible, but it does not really help with the practicality of "querying" such data, so the same caveats apply as explained earlier.
You typically really "mean" to express as "attributes", even if your brain initially thinks "nesting", it's just usually a reaction to how you believe the "previous relational parts" come together. In reality you really need more denormalization.
Also see How to Update Multiple Array Elements in mongodb, since these new update operators actually match and update "multiple array elements" rather than just the first, which has been the previous action of positional updates.
NOTE Somewhat ironically, since this is specified in the "options" argument for .update() and like methods, the syntax is generally compatible with all recent release driver versions.
However this is not true of the mongo shell, since the way the method is implemented there ( "ironically for backward compatibility" ) the arrayFilters argument is not recognized and removed by an internal method that parses the options in order to deliver "backward compatibility" with prior MongoDB server versions and a "legacy" .update() API call syntax.
So if you want to use the command in the mongo shell or other "shell based" products ( notably Robo 3T ) you need a latest version from either the development branch or production release as of 3.6 or greater.
See also positional all $[] which also updates "multiple array elements" but without applying to specified conditions and applies to all elements in the array where that is the desired action.
I know this is a very old question, but I just struggled with this problem myself, and found, what I believe to be, a better answer.
A way to solve this problem is to use Sub-Documents. This is done by nesting schemas within your schemas
MainSchema = new mongoose.Schema({
array1: [Array1Schema]
})
Array1Schema = new mongoose.Schema({
array2: [Array2Schema]
})
Array2Schema = new mongoose.Schema({
answeredBy": [...]
})
This way the object will look like the one you show, but now each array are filled with sub-documents. This makes it possible to dot your way into the sub-document you want. Instead of using a .update you then use a .find or .findOne to get the document you want to update.
Main.findOne((
{
_id: 1
}
)
.exec(
function(err, result){
result.array1.id(12).array2.id(123).answeredBy.push('success')
result.save(function(err){
console.log(result)
});
}
)
Haven't used the .push() function this way myself, so the syntax might not be right, but I have used both .set() and .remove(), and both works perfectly fine.

How do I sort a JSON object by a nested value?

I have an ajax call that returns a JSON object that is pretty complex and I'm having a hard time sorting it.
My call:
$.post('/reports-ajax',arguments, function(data) {}
The response:
{
"10001":{
"unitname":"Fort Worth",
"discounts":{"12-02-2012":"34.810000","12-03-2012":"20.810000","12-04-2012":"27.040000"},
"gross":{"12-02-2012":"56.730000","12-03-2012":"19.350000","12-04-2012":"66.390000"},
"net":{"12-02-2012":"61.920000","12-03-2012":"98.540000","12-04-2012":"39.350000"},
"discounts_total":82.66,
"gross_total":82.47,
"net_total":99.81,
"number":10001
},
"10002":{
"unitname":"Dallast",
"discounts":{"12-02-2012":"12.600000","12-03-2012":"25.780000","12-04-2012":"47.780000","12-05-2012":"45.210000"},
"gross":{"12-02-2012":"29.370000","12-03-2012":"91.110000","12-04-2012":"60.890000","12-05-2012":"51.870000"},
"net":{"12-02-2012":"16.770000","12-03-2012":"65.330000","12-04-2012":"13.110000","12-05-2012":"06.660000"},
"discounts_total":131.37,
"gross_total":33.24,
"net_total":101.87,
"number":10002
},
"32402":{
"unitname":"Austin",
"discounts":{"12-05-2012":"52.890000","12-02-2012":"22.430000","12-03-2012":"58.420000","12-04-2012":"53.130000"},
"gross":{"12-05-2012":"25.020000","12-02-2012":"2836.010000","12-03-2012":"54.740000","12-04-2012":"45.330000"},
"net":{"12-04-2012":"92.200000","12-05-2012":"72.130000","12-02-2012":"13.580000","12-03-2012":"96.320000"},
"discounts_total":186.87,
"gross_total":161.1,
"net_total":174.23,
"number":32402
}
}
I go over the function with a standard each call and do some awesome stuff with highcharts but now I'm trying to sort the responses by the net_total call and I can't figure it out.
I tried .sort() and it errors out that its not a function. I've been reading for a while but guess I'm not finding the right results. This looked promising: Sorting an array of JavaScript objects but it failed with the .sort is not a function. It seems most .sort are on [] arrays not full objects..
Any help would be greatly appreciated.
Sorting objects doesn't make sense since object keys have no positional value. For example, this:
{ a:1, b:2 }
and this:
{ b:2, a:1 }
are exactly the same object. They're not just similar, they're the same.
Nothing in javascript per se gives object keys any positional value. Some people perhaps are mistaken in the belief that:
for (var key in obj) {
iterates through the object keys in a specific sequence. But this is wrong. You should always assume that the for .. in loop processes object keys in random order, always, all the time.
Obviously, if you're going to write a web browser, you're not going to implement a random number generator to parse a for .. in loop. Therefore most web browsers have an accidental stability to how the for .. in loop processes object keys.
Developers who learn javascript by playing around with the browser may figure out that their browser iterates through objects in alphabetical order for example, or the order the keys were added to the object. But this is totally accidental and cannot be relied upon. The browser vendor may change this behavior in the future without violating any backwards compatability (except with buggy scripts written by people who believe objects have a sort order). Not to mention that different browsers have different implementations of javascript and therefore not necessarily have the same internal key ordering of objects.
All the above is besides the point. "Key sort order" does not make any sense in javascript and any behavior observed is merely implementation detail. In short, javascript object does not have key order, just assume it's random.
Solution
Now, what you're really trying to do is not sort the object (you can't, it doesn't make sense). What you're really trying to do is process the object attributes in a specific order. The solution is to simply create an array (which has sorting order) of object keys and then process the object using that array:
// First create the array of keys/net_total so that we can sort it:
var sort_array = [];
for (var key in Response) {
sort_array.push({key:key,net_total:Response[key].net_total});
}
// Now sort it:
sort_array.sort(function(x,y){return x.net_total - y.net_total});
// Now process that object with it:
for (var i=0;i<sort_array.length;i++) {
var item = Response[sort_array[i].key];
// now do stuff with each item
}
What you have there isn't an array and has no order, so you'll have to transform it into an array so you can give it order.
Vaguely:
var array = [];
$.each(data, function(key, value) {
array.push(value);
});
array.sort(function(a, b) {
return a.net_total - b.net_total;
});
Live Example | Source
As GolezTroi points out in the comments, normally the above would lose the key that each entry is stored under in data and so you'd add it back in the first $.each loop above, but in this case the entries already have the key on them (as number), so there's no need.
Or you can replace the first $.each with $.map:
var array = $.map(data, function(entry) {
return entry;
});
// ...and then sort etc.
...whichever you prefer.

Is the order of elements in a JSON list preserved?

I've noticed the order of elements in a JSON object not being the original order.
What about the elements of JSON lists? Is their order maintained?
Yes, the order of elements in JSON arrays is preserved. From RFC 7159 -The JavaScript Object Notation (JSON) Data Interchange Format
(emphasis mine):
An object is an unordered collection of zero or more name/value
pairs, where a name is a string and a value is a string, number,
boolean, null, object, or array.
An array is an ordered sequence of zero or more values.
The terms "object" and "array" come from the conventions of
JavaScript.
Some implementations do also preserve the order of JSON objects as well, but this is not guaranteed.
The order of elements in an array ([]) is maintained. The order of elements (name:value pairs) in an "object" ({}) is not, and it's usual for them to be "jumbled", if not by the JSON formatter/parser itself then by the language-specific objects (Dictionary, NSDictionary, Hashtable, etc) that are used as an internal representation.
Practically speaking, if the keys were of type NaN, the browser will not change the order.
The following script will output "One", "Two", "Three":
var foo={"3":"Three", "1":"One", "2":"Two"};
for(bar in foo) {
alert(foo[bar]);
}
Whereas the following script will output "Three", "One", "Two":
var foo={"#3":"Three", "#1":"One", "#2":"Two"};
for(bar in foo) {
alert(foo[bar]);
}
Some JavaScript engines keep keys in insertion order. V8, for instance, keeps all keys in insertion order except for keys that can be parsed as unsigned 32-bit integers.
This means that if you run either of the following:
var animals = {};
animals['dog'] = true;
animals['bear'] = true;
animals['monkey'] = true;
for (var animal in animals) {
if (animals.hasOwnProperty(animal)) {
$('<li>').text(animal).appendTo('#animals');
}
}
var animals = JSON.parse('{ "dog": true, "bear": true, "monkey": true }');
for (var animal in animals) {
$('<li>').text(animal).appendTo('#animals');
}
You'll consistently get dog, bear, and monkey in that order, on Chrome, which uses V8. Node.js also uses V8. This will hold true even if you have thousands of items. YMMV with other JavaScript engines.
Demo here and here.
"Is the order of elements in a JSON list maintained?" is not a good question. You need to ask "Is the order of elements in a JSON list maintained when doing [...] ?"
As Felix King pointed out, JSON is a textual data format. It doesn't mutate without a reason. Do not confuse a JSON string with a (JavaScript) object.
You're probably talking about operations like JSON.stringify(JSON.parse(...)). Now the answer is: It depends on the implementation. 99%* of JSON parsers do not maintain the order of objects, and do maintain the order of arrays, but you might as well use JSON to store something like
{
"son": "David",
"daughter": "Julia",
"son": "Tom",
"daughter": "Clara"
}
and use a parser that maintains order of objects.
*probably even more :)

How to keep an Javascript object/array ordered while also maintaining key lookups?

I have some data which I originally stored in a generic Javascript object, with the ID as a key:
{
"7": {"id":"7","name":"Hello"},
"3": {"id":"3","name":"World"},
...
}
However, I discovered that browsers do not guarantee a particular object order when looping through them, so in the above "3" would come before "7". I switched to using an array format like this:
[
{"id":"7","name":"Hello"},
{"id":"3","name":"World"},
...
]
Now, I can loop in the correct order but cannot do fast lookups, e.g. data["3"] without having to loop through the array.
Is there a good way to combine both approaches? I would rather avoid using a separate object for each format, because the object is pretty large (hundreds of elements).
I have run across this problem as well. A solution is to keep an ordered array of keys in addition to the original object.
var objects = {
"7": {"id":"7","name":"Hello"},
"3": {"id":"3","name":"World"},
...
}
var order = [ "3", "7", ... ];
Now if you want the second element you can do this lookup:
var second_object = objects[order[1]];
The ECMA standard does not say anything about the order of the elements in an object. And specifically Chrome reorders the keys when they look like numbers.
Example:
var example = {
"a": "a",
"b": "b",
"1": "1",
"2": "2"
};
if you print this in Chrome will get something like:
{
1: "1",
2: "2",
"a": "a",
"b": "b"
};
It's a little sour .. but life.
You could use the solution Andy linked as well, basically wrapping these two together in one object.
An alternative that I use a lot is a custom map function that allows you to specify the order in which the object is traversed. Typically you will do sorting when you're printing your data to the user so while you loop and create your table rows (for instance) your iterator will pass the rows in the order your sort function specifies. I thought it was a nice idea :)
The signature looks like:
function map(object, callback, sort_function);
Example usage:
map(object, function (row) {
table.add_row(row.header, row.value);
}, function (key1, key2) {
return object[key1] - object[key2];
});
Rather than coding your own, there are off-the-shelf libraries available to provide "as provided" JSON parsing or "consistently sorted" JSON printing for display.
You might well consider either of these:
The 'json-order' package offers parsing, formatting & pretty-printing with stable ordering. This is based on having ordered input.
The 'fast-json-stable-stringify' package offers deterministic formatting based on sorting.

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