Related
The array looks like:
var test = [
{
Time: new Date(1000),
psi:100.0
},
{
Time: new Date(1000),
psi:200.0
},
{
Time: new Date(2000),
psi:200.0
}
]
The function looks like (the function was copied from some online resource, couldn't find the exact reference.)
function uniqTimetable(nums){
console.log(nums); //log#1
var length = nums.length;
var count = 0;
for (var i =0; i< length-1; i++){
if (nums[count].Time.getTime() !== nums[i+1].Time.getTime()){
count ++;
nums[count] = nums[i+1];
}
}
nums.length = count + 1;
console.log(nums); // log #2
}
uniqTimetable(test);
console.log(test);// log #3
Are there any problems of
copy one object to the other array member by this linenums[count] = nums[i+1]
rescale the array length by this linenums.length = count + 1
?
With electron/node.js, the output looks a bit weird.
In log#1, it shows the array length is 2 instead of 3. Something seems wrong with the function. Any suggestions welcome.
Thanks in advance.
If I understood the problem, you can solve it in one line function:
const test = [{
Time: new Date(1000),
psi: 100.0
},
{
Time: new Date(1000),
psi: 200.0
},
{
Time: new Date(2000),
psi: 200.0
}
]
const unique = test.filter(({Time}, i, array) =>
!array.find((item, j) => item.Time.getTime() === Time.getTime() && j > i));
console.log(unique);
(I assumed psi is not relevant)
It uses find and filter array's methods.
function removeDuplicates(myArr, prop) {
return myArr.filter((obj, pos, arr) => {
return arr.map(mapObj => mapObj[prop]).indexOf(obj[prop]) === pos;
});
}
removeDuplicates(test,"Time")
Using the filter function of javascript, to return the List of only unique elements.
I like #Akin's answer! But unfortunately the .indexOf() function does not work for Date objects with the same value, since each object is still considered to be different and the .indexOf() function will always find the index of the Date object itself and never another "copy". To overcome this I convert the Date object back to milliseconds before collecting the values in an array (tst). I do this with myArr.map(mapObj => mapObj[prop].getTime()) before I go into the .filter function.
As the .getTime() method will only work for Date objects it does not make sense to keep the property prop as an argument. Instead I hardcoded the .Time property into the code.
Edit:
By coercing a numerical data type with a unary operator + for the .Time property I can leave out the .getTime() method which will be applied implicitly.
var test = [{Time: new Date(1000), psi:100.0},
{Time: new Date(1000), psi:200.0},
{Time: new Date(2000), psi:200.0}];
function Cars10m_remDups(myArr) {
let tst=myArr.map(o=>+o.Time);
return myArr.filter((o, i)=>tst.indexOf(+o.Time)===i);
}
// for comparison: --> will list all three objects!
function Akin_remDups(myArr, prop) {
return myArr.filter((obj, pos, arr) => {
return arr.map(mapObj => mapObj[prop]).indexOf(obj[prop]) === pos;
});
}
// Zero's one-liner works too, here: my shortened version
const Zero_remDups = myArr => myArr.filter(({Time}, i, array) =>
!array.find((item, j) => +item.Time-Time==0&&i>j));
// also: with "i>j" I pick the first unique (Zero chose the last)
console.log('Cars10m:',Cars10m_remDups(test));
console.log('Akin:',Akin_remDups(test,"Time"));
console.log('Zero:',Zero_remDups(test));
.as-console-wrapper { max-height: 100% !important; top: 0; }
i've got an Array like this
(1) var values = [2014.02.01", "2014.03.01", "2014.03.01", "2014.03.01", "2014.03.01", "2014.03.17", "2014.04.01", "2014.04.01", "2014.04.09",...];
and i want to count the dates and create a object in that format
(2) count = {01.02.2014: 1, 01.03.2014: 4, 17.03.2014: 1, 01.04.2014: 2, 09.04.2014: 1,...}
i tried it in that way but this don't sort the object in the wright way
(3) values.forEach(function(i) { count[i] = (count[i]||0)+1; });
the result isn't sorted...is there a way to create a object with sorted dates? I already sort the array before creating the object but it doesn't work
edit:
reversing dates is no problem
for (var j=0; j<values.length; j++){
values[j] = values[j].split(".").reverse().join(".");
}
but creating the object that is sorted by date is the problem...my way (3) doesn't sort the object
// group the data by date and count the appearances
var grouped = values.reduce(function(l, r) {
l[r] = (l[r] || 0) + 1;
return l;
}, {});
// as objects can't be sorted, map it to an array of objects with the desired data as properties
var groupedAndSorted = Object.keys(grouped).map(function(key) {
return { "date": key, "count": grouped[key] };
}).sort(function(a, b) {
return a.date > b.date;
});
// [{"date":"2014.02.01","count":1},{"date":"2014.03.01","count":4},{"date":"2014.03.17","count":1},{"date":"2014.04.01","count":2},{"date":"2014.04.09","count":1}]
You can do it by following the functional way which tends to be more sexy, shorter. To handle this, you can simulate an hashmap key/value.
You can use Array.prototype.reduce() which is a powerful method.
//Reduce our data and initialize our result to an empty object
//Sort values input and perform reduce
var count = values.sort().reduce(function(result, current){
//Format our key
var key = current.split('.').reverse('').join('.');
//Set value to our object
result[key] = (++result[key] || 1);
return result;
}, {});
console.log(count);
EDIT
I've had key formatting for out object.
You should sort the dates using a compare function that simply strips the periods before rearranging them:
var arr = ["2014.02.01", "2014.03.01", "2014.03.01", "2014.03.01", "2014.03.01", "2014.03.17", "2014.04.01", "2014.04.01", "2014.04.09"]
arr.sort(function(a, b) {
return (a.replace('.','') - b.replace('.',''));
}).forEach(function(v,i){arr[i] = v.split('.').reverse().join(".")});
document.write(arr.join('<br>'));
All thats required next is to turn the array into an object with a count of the recurring dates, which can also reverse the values in each string:
arr = arr.sort(function(a, b) {
return (a.replace('.','') - b.replace('.',''));
}).reduce(function(obj, v){
v = v.split('.').reverse().join('.')
if (!obj.hasOwnProperty(v)) {
obj[v] = 0;
}
++obj[v];
return obj;
},{});
But be warned, there is no guarantee that you'll get consistent ordering. In the latest version of the language specification, order is based firstly on numeric order if the property is a number, then the order properties are added. The Safari console thinks the keys are numbers so returns the following order:
Object { 01.02.2014: 1, 01.03.2014: 4, 01.04.2014: 2, 09.04.2014: 1, 17.03.2014: 1 }
but when stringified with JSON.stringify or the keys are returned by Object.keys, they're in the same order as Firefox and Chrome which return:
Object { 01.02.2014: 1, 01.03.2014: 4, 17.03.2014: 1, 01.04.2014: 2, 09.04.2014: 1 }
which is consistent with ECMAScript 2015.
To get consistent ordering, you should use ISO 8601 like dates similar to the original but without the periods. But best of all, you should not expect the order to be consistent or predictable, because it across browsers in use (unless you restrict yourself to one particular implementation that does what you want).
I have built an object in PHP, used JSON_encode function and send it as a JSON string to my JS script via ajax. Then I convert it back to an object. The problem I am having is that I wanted to keep the object in the order that it was originally created in. Please see this picture of what the object looks like once I get it into JS:
When I created the object, it was sorted by the customer field alphabetically. The customer name starting with A would come first, B second, etc. As you can see, now, the first element of the object as customer starting with S. It looks like somehow it got automatically sorted by the key of the top-level object, which is an integer, so I understand why this happened.
So i want to do is re-sort this object so that all the sub-objects are sorted by the customer field alphabetically. Is this possible? If so, how do I do it?
Thanks!
I've changed Fabricio Matée answer to become more flexible and return the sorted object.
function alphabetical_sort_object_of_objects(data, attr) {
var arr = [];
for (var prop in data) {
if (data.hasOwnProperty(prop)) {
var obj = {};
obj[prop] = data[prop];
obj.tempSortName = data[prop][attr].toLowerCase();
arr.push(obj);
}
}
arr.sort(function(a, b) {
var at = a.tempSortName,
bt = b.tempSortName;
return at > bt ? 1 : ( at < bt ? -1 : 0 );
});
var result = [];
for (var i=0, l=arr.length; i<l; i++) {
var obj = arr[i];
delete obj.tempSortName;
for (var prop in obj) {
if (obj.hasOwnProperty(prop)) {
var id = prop;
}
}
var item = obj[id];
result.push(item);
}
return result;
}
Then just call the function like this
your_object = alphabetical_sort_object_of_objects(your_object, 'attribute_to_sort');
It's probably the difference between a JavaScript Object and a JavaScript Array. Objects are more like hash tables, where the keys aren't sorted in any particular order, whereas Arrays are linear collections of values.
In your back end, make sure you're encoding an array, rather than an object. Check the final encoded JSON, and if your collection of objects is surrounded by {} instead of [], it's being encoded as an object instead of an array.
You may run into a problem since it looks like you're trying to access the objects by an ID number, and that's the index you want those objects to occupy in the final array, which presents another problem, because you probably don't want an array with 40,000 entries when you're only storing a small amount of values.
If you just want to iterate through the objects, you should make sure you're encoding an array instead of an object. If you want to access the objects by specific ID, you'll probably have to sort the objects client-side (i.e. have the object from the JSON response, and then create another array and sort those objects into it, so you can have the sorted objects and still be able to access them by id).
You can find efficient sorting algorithms (or use the one below from ELCas) easily via Google.
Here's a generic iteration function which pushes all objects into an array and sorts them by their customer property in a case-insensitive manner, then iterates over the sorted array:
function iterate(data) {
var arr = [];
for (var prop in data) {
if (data.hasOwnProperty(prop)) {
var obj = {};
obj[prop] = data[prop];
obj.tempSortName = data[prop].customer.toLowerCase();
arr.push(obj);
}
}
arr.sort(function(a, b) {
var at = a.tempSortName,
bt = b.tempSortName;
return at > bt ? 1 : ( at < bt ? -1 : 0 );
});
for (var i = 0, l = arr.length; i < l; i++) {
var obj = arr[i];
delete obj.tempSortName;
console.log(obj);
for (var prop in obj) {
if (obj.hasOwnProperty(prop)) {
var id = prop; //gets the obj "index" (id?)
}
}
console.log(id);
var item = obj[id];
console.log(item.customer);
//do stuff with item
}
}
Fiddle
sortObject(object){
if(typeof object === 'object'){
if(object instanceof Date){
return object;
}
if(object instanceof Array){
return object.map(element => this.sortObject(element));
} else {
return Object.keys(object).sort().reduce((result, key) => {
if(object[key] && object[key] !== null) {
result[key] = this.sortObject(object[key]);
}
return result;
}, {});
}
}
return object;
}
I have a JavaScript array like this:
var myData=['237','124','255','124','366','255'];
I need the array elements to be unique and sorted:
myData[0]='124';
myData[1]='237';
myData[2]='255';
myData[3]='366';
Even though the members of array look like integers, they're not integers, since I have already converted each to be string:
var myData[0]=num.toString();
//...and so on.
Is there any way to do all of these tasks in JavaScript?
This is actually very simple. It is much easier to find unique values, if the values are sorted first:
function sort_unique(arr) {
if (arr.length === 0) return arr;
arr = arr.sort(function (a, b) { return a*1 - b*1; });
var ret = [arr[0]];
for (var i = 1; i < arr.length; i++) { //Start loop at 1: arr[0] can never be a duplicate
if (arr[i-1] !== arr[i]) {
ret.push(arr[i]);
}
}
return ret;
}
console.log(sort_unique(['237','124','255','124','366','255']));
//["124", "237", "255", "366"]
You can now achieve the result in just one line of code.
Using new Set to reduce the array to unique set of values.
Apply the sort method after to order the string values.
var myData=['237','124','255','124','366','255']
var uniqueAndSorted = [...new Set(myData)].sort()
UPDATED for newer methods introduced in JavaScript since time of question.
This might be adequate in circumstances where you can't define the function in advance (like in a bookmarklet):
myData.sort().filter(function(el,i,a){return i===a.indexOf(el)})
Here's my (more modern) approach using Array.protoype.reduce():
[2, 1, 2, 3].reduce((a, x) => a.includes(x) ? a : [...a, x], []).sort()
// returns [1, 2, 3]
Edit: More performant version as pointed out in the comments:
arr.sort().filter((x, i, a) => !i || x != a[i-1])
function sort_unique(arr) {
return arr.sort().filter(function(el,i,a) {
return (i==a.indexOf(el));
});
}
How about:
array.sort().filter(function(elem, index, arr) {
return index == arr.length - 1 || arr[index + 1] != elem
})
This is similar to #loostro answer but instead of using indexOf which will reiterate the array for each element to verify that is the first found, it just checks that the next element is different than the current.
Try using an external library like underscore
var f = _.compose(_.uniq, function(array) {
return _.sortBy(array, _.identity);
});
var sortedUnique = f(array);
This relies on _.compose, _.uniq, _.sortBy, _.identity
See live example
What is it doing?
We want a function that takes an array and then returns a sorted array with the non-unique entries removed. This function needs to do two things, sorting and making the array unique.
This is a good job for composition, so we compose the unique & sort function together. _.uniq can just be applied on the array with one argument so it's just passed to _.compose
the _.sortBy function needs a sorting conditional functional. it expects a function that returns a value and the array will be sorted on that value. Since the value that we are ordering it by is the value in the array we can just pass the _.identity function.
We now have a composition of a function that (takes an array and returns a unique array) and a function that (takes an array and returns a sorted array, sorted by their values).
We simply apply the composition on the array and we have our uniquely sorted array.
This function doesn't fail for more than two duplicates values:
function unique(arr) {
var a = [];
var l = arr.length;
for(var i=0; i<l; i++) {
for(var j=i+1; j<l; j++) {
// If a[i] is found later in the array
if (arr[i] === arr[j])
j = ++i;
}
a.push(arr[i]);
}
return a;
};
Here is a simple one liner with O(N), no complicated loops necessary.
> Object.keys(['a', 'b', 'a'].reduce((l, r) => l[r] = l, {})).sort()
[ 'a', 'b' ]
Explanation
Original data set, assume its coming in from an external function
const data = ['a', 'b', 'a']
We want to group all the values onto an object as keys as the method of deduplication. So we use reduce with an object as the default value:
[].reduce(fn, {})
The next step is to create a reduce function which will put the values in the array onto the object. The end result is an object with a unique set of keys.
const reduced = data.reduce((l, r) => l[r] = l, {})
We set l[r] = l because in javascript the value of the assignment expression is returned when an assignment statement is used as an expression. l is the accumulator object and r is the key value. You can also use Object.assign(l, { [r]: (l[r] || 0) + 1 }) or something similar to get the count of each value if that was important to you.
Next we want to get the keys of that object
const keys = Object.keys(reduced)
Then simply use the built-in sort
console.log(keys.sort())
Which is the set of unique values of the original array, sorted
['a', 'b']
The solution in a more elegant way.
var myData=['237','124','255','124','366','255'];
console.log(Array.from(new Set(myData)).sort((a,b) => a - b));
I know the question is very old, but maybe someone will come in handy
A way to use a custom sort function
//func has to return 0 in the case in which they are equal
sort_unique = function(arr,func) {
func = func || function (a, b) {
return a*1 - b*1;
};
arr = arr.sort(func);
var ret = [arr[0]];
for (var i = 1; i < arr.length; i++) {
if (func(arr[i-1],arr[i]) != 0)
ret.push(arr[i]);
}
}
return ret;
}
Example: desc order for an array of objects
MyArray = sort_unique(MyArray , function(a,b){
return b.iterator_internal*1 - a.iterator_internal*1;
});
No redundant "return" array, no ECMA5 built-ins (I'm pretty sure!) and simple to read.
function removeDuplicates(target_array) {
target_array.sort();
var i = 0;
while(i < target_array.length) {
if(target_array[i] === target_array[i+1]) {
target_array.splice(i+1,1);
}
else {
i += 1;
}
}
return target_array;
}
I guess I'll post this answer for some variety. This technique for purging duplicates is something I picked up on for a project in Flash I'm currently working on about a month or so ago.
What you do is make an object and fill it with both a key and a value utilizing each array item. Since duplicate keys are discarded, duplicates are removed.
var nums = [1, 1, 2, 3, 3, 4, 5, 5, 6, 7, 7, 8, 9, 9, 10];
var newNums = purgeArray(nums);
function purgeArray(ar)
{
var obj = {};
var temp = [];
for(var i=0;i<ar.length;i++)
{
obj[ar[i]] = ar[i];
}
for (var item in obj)
{
temp.push(obj[item]);
}
return temp;
}
There's already 5 other answers, so I don't see a need to post a sorting function.
// Another way, that does not rearrange the original Array
// and spends a little less time handling duplicates.
function uniqueSort(arr, sortby){
var A1= arr.slice();
A1= typeof sortby== 'function'? A1.sort(sortby): A1.sort();
var last= A1.shift(), next, A2= [last];
while(A1.length){
next= A1.shift();
while(next=== last) next= A1.shift();
if(next!=undefined){
A2[A2.length]= next;
last= next;
}
}
return A2;
}
var myData= ['237','124','255','124','366','255','100','1000'];
uniqueSort(myData,function(a,b){return a-b})
// the ordinary sort() returns the same array as the number sort here,
// but some strings of digits do not sort so nicely numerical.
function sort() only is only good if your number has same digit, example:
var myData = ["3","11","1","2"]
will return;
var myData = ["1","11","2","3"]
and here improvement for function from mrmonkington
myData.sort().sort(function(a,b){return a - b;}).filter(function(el,i,a){if(i==a.indexOf(el) & el.length>0)return 1;return 0;})
the above function will also delete empty array and you can checkout the demo below
http://jsbin.com/ahojip/2/edit
O[N^2] solutions are bad, especially when the data is already sorted, there is no need to do two nested loops for removing duplicates. One loop and comparing to the previous element will work great.
A simple solution with O[] of sort() would suffice. My solution is:
function sortUnique(arr, compareFunction) {
let sorted = arr.sort(compareFunction);
let result = sorted.filter(compareFunction
? function(val, i, a) { return (i == 0 || compareFunction(a[i-1], val) != 0); }
: function(val, i, a) { return (i == 0 || a[i-1] !== val); }
);
return result;
}
BTW, can do something like this to have Array.sortUnique() method:
Array.prototype.sortUnique = function(compareFunction) {return sortUnique(this, compareFunction); }
Furthermore, sort() could be modified to remove second element if compare() function returns 0 (equal elements), though that code can become messy (need to revise loop boundaries in the flight). Besides, I stay away from making my own sort() functions in interpreted languages, since it will most certainly degrade the performance. So this addition is for the ECMA 2019+ consideration.
The fastest and simpleness way to do this task.
const N = Math.pow(8, 8)
let data = Array.from({length: N}, () => Math.floor(Math.random() * N))
let newData = {}
let len = data.length
// the magic
while (len--) {
newData[data[len]] = true
}
var array = [2,5,4,2,5,9,4,2,6,9,0,5,4,7,8];
var unique_array = [...new Set(array)]; // [ 2, 5, 4, 9, 6, 0, 7, 8 ]
var uniqueWithSorted = unique_array.sort();
console.log(uniqueWithSorted);
output = [ 0, 2, 4, 5, 6, 7, 8, 9 ]
Here, we used only Set for removing duplicity from the array and then used sort for sorting array in ascending order.
I'm afraid you can't combine these functions, ie. you gotta do something like this:-
myData.unique().sort();
Alternatively you can implement a kind of sortedset (as available in other languages) - which carries both the notion of sorting and removing duplicates, as you require.
Hope this helps.
References:-
Array.sort
Array.unique
is there a data structure or a pattern in Javascript that can be used for both fast lookup (by key, as with associative arrays) and for ordered looping?
Right, now I am using object literals to store my data but I just disovered that Chrome does not maintain the order when looping over the property names.
Is there a common way to solve this in Javascript?
Thanks for any hints.
Create a data structure yourselves. Store the ordering in an array that is internal to the structure. Store the objects mapped by a key in a regular object. Let's call it OrderedMap which will have a map, an array, and four basic methods.
OrderedMap
map
_array
set(key, value)
get(key)
remove(key)
forEach(fn)
function OrderedMap() {
this.map = {};
this._array = [];
}
When inserting an element, add it to the array at the desired position as well as to the object. Insertion by index or at the end is in O(1).
OrderedMap.prototype.set = function(key, value) {
// key already exists, replace value
if(key in this.map) {
this.map[key] = value;
}
// insert new key and value
else {
this._array.push(key);
this.map[key] = value;
}
};
When deleting an object, remove it from the array and the object. If deleting by a key or a value, complexity is O(n) since you will need to traverse the internal array that maintains ordering. When deleting by index, complexity is O(1) since you have direct access to the value in both the array and the object.
OrderedMap.prototype.remove = function(key) {
var index = this._array.indexOf(key);
if(index == -1) {
throw new Error('key does not exist');
}
this._array.splice(index, 1);
delete this.map[key];
};
Lookups will be in O(1). Retrieve the value by key from the associative array (object).
OrderedMap.prototype.get = function(key) {
return this.map[key];
};
Traversal will be ordered and can use either of the approaches. When ordered traversal is required, create an array with the objects (values only) and return it. Being an array, it would not support keyed access. The other option is to ask the client to provide a callback function that should be applied to each object in the array.
OrderedMap.prototype.forEach = function(f) {
var key, value;
for(var i = 0; i < this._array.length; i++) {
key = this._array[i];
value = this.map[key];
f(key, value);
}
};
See Google's implementation of a LinkedMap from the Closure Library for documentation and source for such a class.
The only instance in which Chrome doesn't maintain the order of keys in an object literal seems to be if the keys are numeric.
var properties = ["damsonplum", "9", "banana", "1", "apple", "cherry", "342"];
var objLiteral = {
damsonplum: new Date(),
"9": "nine",
banana: [1,2,3],
"1": "one",
apple: /.*/,
cherry: {a: 3, b: true},
"342": "three hundred forty-two"
}
function load() {
var literalKeyOrder = [];
for (var key in objLiteral) {
literalKeyOrder.push(key);
}
var incremental = {};
for (var i = 0, prop; prop = properties[i]; i++) {
incremental[prop] = objLiteral[prop];
}
var incrementalKeyOrder = [];
for (var key in incremental) {
incrementalKeyOrder.push(key);
}
alert("Expected order: " + properties.join() +
"\nKey order (literal): " + literalKeyOrder.join() +
"\nKey order (incremental): " + incrementalKeyOrder.join());
}
In Chrome, the above produces: "1,9,342,damsonplum,banana,apple,cherry".
In other browsers, it produces "damsonplum,9,banana,1,apple,cherry,342".
So unless your keys are numeric, I think even in Chrome, you're safe. And if your keys are numeric, maybe just prepend them with a string.
As
has been noted, if your keys are numeric
you can prepend them with a string to preserve order.
var qy = {
_141: '256k AAC',
_22: '720p H.264 192k AAC',
_84: '720p 3D 192k AAC',
_140: '128k AAC'
};
Example