Develop Reference

Sorting occurrences of an array, high to low. Then return the top 4 highest occurrences [duplicate]

What is an elegant way to take a javascript array, order by the frequency of the values, and then filter for uniques?
So,
["apples", "oranges", "oranges", "oranges", "bananas", "bananas", "oranges"]
becomes
["oranges, "bananas", "apples"]

Compute the frequency of each item first.
{
apples: 1,
oranges: 4,
bananas: 2
}
Then create an array from this frequency object which will also remove the duplicates.
["apples", "oranges", "bananas"]
Now sort this array in descending order using the frequency map we created earlier.
function compareFrequency(a, b) {
return frequency[b] - frequency[a];
}
array.sort(compareFrequency);
Here's the entire source (using the newly introduced Array functions in ECMA 5) and combining the de-duplication and frequency map generation steps,
function sortByFrequency(array) {
var frequency = {};
array.forEach(function(value) { frequency[value] = 0; });
var uniques = array.filter(function(value) {
return ++frequency[value] == 1;
});
return uniques.sort(function(a, b) {
return frequency[b] - frequency[a];
});
}
Same as above using the regular array iteration.
function sortByFrequencyAndRemoveDuplicates(array) {
var frequency = {}, value;
// compute frequencies of each value
for(var i = 0; i < array.length; i++) {
value = array[i];
if(value in frequency) {
frequency[value]++;
}
else {
frequency[value] = 1;
}
}
// make array from the frequency object to de-duplicate
var uniques = [];
for(value in frequency) {
uniques.push(value);
}
// sort the uniques array in descending order by frequency
function compareFrequency(a, b) {
return frequency[b] - frequency[a];
}
return uniques.sort(compareFrequency);
}

// returns most frequent to least frequent
Array.prototype.byCount= function(){
var itm, a= [], L= this.length, o= {};
for(var i= 0; i<L; i++){
itm= this[i];
if(!itm) continue;
if(o[itm]== undefined) o[itm]= 1;
else ++o[itm];
}
for(var p in o) a[a.length]= p;
return a.sort(function(a, b){
return o[b]-o[a];
});
}
//test
var A= ["apples","oranges","oranges","oranges","bananas","bananas","oranges"];
A.byCount()
/* returned value: (Array)
oranges,bananas,apples
*/

I was actually working on this at the same time - the solution I came up with is pretty much identical to Anurag's.
However I thought it might be worth sharing as I had a slightly different way of calculating the frequency of occurrences, using the ternary operator and checking if the value has been counted yet in a slightly different way.
function sortByFrequencyAndFilter(myArray)
{
var newArray = [];
var freq = {};
//Count Frequency of Occurances
var i=myArray.length-1;
for (var i;i>-1;i--)
{
var value = myArray[i];
freq[value]==null?freq[value]=1:freq[value]++;
}
//Create Array of Filtered Values
for (var value in freq)
{
newArray.push(value);
}
//Define Sort Function and Return Sorted Results
function compareFreq(a,b)
{
return freq[b]-freq[a];
}
return newArray.sort(compareFreq);
}

Basic strategy:
Create an object to use as a hash table to track the frequency of each item in the array to be sorted.
Create a new array containing the item, frequency pairs.
Sort this array on frequency in descending order.
Extract the items from that array.
Code:
function descendingUniqueSort(toBeSorted) {
var hash = new Object();
toBeSorted.forEach(function (element, index, array) {
if (hash[element] == undefined) {
hash[element] = 1;
}
else {
hash[element] +=1;
}});
var itemCounts = new Array();
for (var key in hash) {
var itemCount = new Object();
itemCount.key = key;
itemCount.count = hash[key];
itemCounts.push(itemCount);
}
itemCounts.sort(function(a,b) { if(a.count<b.count) return 1;
else if (a.count>b.count) return -1; else return 0;});
return itemCounts.map(function(itemCount) { return itemCount.key; });
}

var arr = ["apples", "oranges", "oranges", "oranges", "bananas", "bananas", "oranges"].sort();
var freq = {};
for (var s in arr) freq[s] = freq[s] ? freq[s] + 1 : 0;
arr.sort(function(a, b) { return freq[a] > freq[b] ? -1 : 1; });
for (var i = arr.length - 1; i > 0; i--) if (arr[i] == arr[i - 1]) arr.splice(i,1);
alert(arr.join(","));

for the first step to compute
{
oranges: 4,
bananas: 2,
apples: 1
}
you can use countBy function of underscroe.js
var all=["apples", "oranges", "oranges", "oranges", "bananas", "bananas", "oranges"];
var frequency=_.countBy(all,function(each){return each});
so frequency object will contain frequency of all unique values, and you can get an unique list by simply calling _.uniq(all), and to sort that unique list by the _.sortBy method of underscore and using your frequency object you can use
_.sortBy(_.uniq(all),function(frequencyKey){return -frequency[frequencyKey]});
-ve sign is used here to sort the list in decending order by means of frequency value as per your requirement.
You can check the the documentation of http://underscorejs.org/ for further optimization by your own trick :)

Let me put a minimal code to get unique values (and with frequencies) in ES6.
var arr = ["apples", "oranges", "oranges", "oranges", "bananas", "bananas", "oranges"];
console.log([...new Set(arr)])
It is also applied to array of objects to aggregate some properties.
var arr = [{"fruit":"apples"}, {"fruit":"oranges"}, {"fruit":"oranges"}, {"fruit":"oranges"}, {"fruit":"bananas"}, {"fruit":"bananas"}, {"fruit":"oranges"}];
console.log(arr.reduce((x,y)=>{if(x[y.fruit]) {x[y.fruit]++;return x;} else {var z={};z[y.fruit]=1;return Object.assign(x,z);}},{}))

Create a counter of the array's elements using reduce:
arr.reduce(
(counter, key) => {counter[key] = 1 + counter[key] || 1; return counter},
{}
);
Sort the counter object using sort on Object.entries and finally show only keys.
const arr = ["apples", "oranges", "oranges", "oranges",
"bananas", "bananas", "oranges"
];
// create a counter object on array
let counter = arr.reduce(
(counter, key) => {
counter[key] = 1 + counter[key] || 1;
return counter
}, {});
console.log(counter);
// {"apples": 1, "oranges": 4, "bananas": 2}
// sort counter by values (compare position 1 entries)
// the result is an array
let sorted_counter = Object.entries(counter).sort((a, b) => b[1] - a[1]);
console.log(sorted_counter);
// [["oranges", 4], ["bananas", 2], ["apples", 1]]
// show only keys of the sorted array
console.log(sorted_counter.map(x => x[0]));
// ["oranges", "bananas", "apples"]

Modify an object to a new Array in Javascript

sorry, i m a beginner in javascript.
Can someone explain me how to modify this Object
{toto:[12,13,15],titi:[45,12,34]}
to this Array
newArray = [
{
toto:12,
titi:45
},{
toto:13,
titi:12
},{
toto:15,
titi:34}
]
Also, what the solution if the toto and titi doesn't have the same lenght
Thanks for support!

Here's how I did it. In this way, you don't need to know the names of the keys or the size of the array, but it does require a few loops.
obj = {toto:[12,13,15],titi:[45,12,34]};
newArray = [];
// Find the longest array in your data set
longest = 0;
Object.keys(obj).forEach(function(key) {
if (obj[key].length > longest) {
longest = obj[key].length;
}
});
// Loop through the existing data set to create new objects
for (i = 0; i<longest; i++) {
newObject = {};
Object.keys(obj).forEach(function(key) {
newObject[key] = obj[key][i];
});
newArray.push(newObject);
}
console.log(newArray);
plnkr.co demo in the script.js file.
If you want to ignore keys that would have undefined values for uneven loops, you can add a conditional inside the forEach loop that creates a new object:
Object.keys(obj).forEach(function(key) {
if (obj[key][i] !== undefined) {
newObject[key] = obj[key][i];
}
});

Assuming lengths of toto and titi are the same:
Obj = {toto:[12,13,15],titi:[45,12,34]};
newArray = [];
for (var k in Obj["toto"]) {
newArray.push({ toto:Obj["toto"][k],titi:Obj["titi"][k] });
}

Since the lengths of your inner arrays are equal, you should be able to simply loop through them and add a value from each array (for each iteration) into a new array :
// Your input
var input = {toto:[12,13,15],titi:[45,12,34]};
// An array to store your output
var output = [];
// Since your inner arrays are of equal size, you can loop through them
// as follows
for(var i = 0; i < input.toto.length; i++){
output.push({ toto: input.toto[i], titi: input.titi[i]});
}
You can see a working example of this here and what the output array looks like below :

A more generic approach
var object = { toto: [12, 13, 15], titi: [45, 12, 34] },
newArray = function (o) {
var keys = Object.keys(o),
l = keys.reduce(function (r, a) { return Math.max(r, o[a].length); }, 0),
i = 0,
t,
result = [];
while (i < l) {
t = {};
keys.forEach(function (k) { t[k] = o[k][i]; });
result.push(t);
i++;
}
return result;
}(object);
document.write('<pre>' + JSON.stringify(newArray, 0, 4) + '</pre>');

Merge array of javascript objects by property key

First of all: I already found this thread, which basically is exactly what I want, but I tried my best to apply it to my needs - I couldn't.
So, I have the following javascript function:
function loadRelationData(object) {
var result = [];
var parents = []
parents = getParentObjectsByObjectID(object['ObjectID']);
var tmpFirstObjects = [];
var tmpOtherObjects = [];
$.each(parents, function (_, parent) {
var keyName = 'Übergeordnete ' + parent['ObjectType'];
var pushObject = {};
if (parent['ObjectType'] == object['ObjectType']) {
pushObject['Fieldname'] = keyName;
pushObject['Value'] = parent['Name'];
tmpFirstObjects.push(pushObject);
} else {
pushObject['Fieldname'] = keyName;
pushObject['Value'] = parent['Name'];
tmpOtherObjects.push(pushObject);
}
});
result = result.concat(tmpFirstObjects).concat(tmpOtherObjects);
return result;
}
The parents array looks like this
And my function creates this result
This might be a bit complicated, but I need to split it up like this, because I need the order.
What I want is an array with both "TEC_MapLocations" joined together like this:
[
{Fieldname: 'Übergeordnete TEC_Equipment', Value: 'E0192'},
{Fieldname: 'Übergeordnete TEC_MapLocation', Value: ['M100', 'M200']},
{Fieldname: 'Übergeordnete TEC_FunctionalLocation', Value: 'FL456'}
]
Any ideas on how to alter my code to achieve the desired result right away or how to merge the results array?
edit: I used Joseph's solution and used the following (quick and dirty) sort function to get back my desired sorting:
output.sort(function (a, b) {
if (a.ObjectType == object.ObjectType) {
return -1
} else {
return 1
}
});

What you'd want to do first is build a hash with Fieldname as key, and an array as value. Then you'd want to use reduce to add the values into the hash and array. Then you can transform it into an array using Object.keys and map.
var input = [
{Name: 'M100', ObjectID: 1, ObjectType: 'TEC_MapLocation'},
{Name: 'M200', ObjectID: 2, ObjectType: 'TEC_MapLocation'},
{Name: 'FL456', ObjectID: 4, ObjectType: 'TEC_FunctionalLocation'},
{Name: 'E0192', ObjectID: 5, ObjectType: 'TEC_Equipment'}
];
var hash = input.reduce(function(carry, item){
// Create the name
var name = 'Übergeordnete ' + item.ObjectType;
// If array with name doesn't exist, create it
if(!carry[name]) carry[name] = [];
// If item isn't in the array, add it.
if(!~carry[name].indexOf(item.Name)) carry[name].push(item.Name);
return carry;
}, {});
// Convert the hash into an array
var output = Object.keys(hash).map(function(key, index, array){
return { Fieldname: key, Value: hash[key] }
});
document.write(JSON.stringify(output));

Try this:
function joinObjects( array ) {
// Start with empty array
var ret = new Array();
// Iterate array
for ( var i = 0; i < array.length; i++ ) {
// Search by fieldname
var match = false;
var j;
for ( j = 0; j < ret.length; j++ ) {
if ( array[i].Fieldname == ret[j].Fieldname ) { match = true; break; }
}
// If not exists
if ( !match ) {
// Intert object
ret.push({
Fieldname: array[i].Fieldname,
Value: new Array()
});
}
// Insert value
ret[j].Value.push( array[i].Value );
}
// Return new array
return ret;
}
http://jsfiddle.net/6entfv4x/

Comparing an Array with an Objects' Array in JavaScript

I am new to JavaScript and wondering how can I compare an array with another array consists of JavaScript objects.
The array is a series of sorted time in the "YYYY-MM-DD" format.
The array of objects missed some price values of several days.
I want to find the missed value and assign it as "NULL".
For example, I have an array as:
array = ['2014-10-09','2014-10-10','2014-10-11','2014-10-12'];
and an array with objects as:
objArray = [{
date:"2014-10-09",
price:"100"
},
{
date:"2014-10-10",
price:"99"
},
{
date:"2014-10-12",
price:"102"
}];
I want to get the price array in this way:
priceResult = [100, 99, "NULL", 102];
What would be the most efficient way without using other libraries? I wanted to see if anyone had a more elegant solution. I deeply appreciate your help.

You can create a lookup set from the object array, then you can use that to translate the dates to prices.
This scales well, as it is an O(n+m) solution rather than the O(n*m) solution that you get if you use a loop in a loop to find the prices.
var array = ['2014-10-09','2014-10-10','2014-10-11','2014-10-12'];
var objArray = [{ date:"2014-10-09", model:"A", price:"100" },{ date:"2014-10-10", model:"A", price:"99" },{ date:"2014-10-12", model:"A", price:"102" }];
var lookup = {};
for (var i = 0; i < objArray.length; i++) {
lookup[objArray[i].date] = parseInt(objArray[i].price, 10);
}
var priceResult = [];
for (var i = 0; i < array.length; i++) {
if (lookup.hasOwnProperty(array[i])) {
priceResult.push(lookup[array[i]]);
} else {
priceResult.push('NULL');
}
}
// output result in StackOverflow snippet
document.write(JSON.stringify(priceResult));
Note: Instead of the string 'NULL' you might want to use the value null instead, as it is generally easier to handle.

lodash is the best library for this. But you did say "without using other libraries", so you will need to do it natively.
The easiest way to do it is nested for loops:
var i, j, d, res = [];
for (i=0; i<dateArray.length; i++) {
d = dateArray[i];
for (j=0; j<objArray.length; j++) {
if (objArray[j] && objArray[j].date && objArray[j].date === d) {
res.push(objArray[j].price);
j = objArray.length; // don't waste energy searching any more, since we found it
}
}
}
// res now contains all you wanted
If objArray is really big, and you don't want to search it multiple times, then you could turn it into an object indexed by date:
var i, obj = {}, d, res = [];
for (i=0; i<objArray.length; i++) {
if (objArray[i] && objArray[i].date) {
obj[objArray[i].date] = objArray[i];
}
}
for (i=0; i<dateArray.length; i++) {
d = dateArray[i];
res.push(obj[d] ? obj[d].price : null : null);
}
// res now contains all you wanted

Loop trough the object and search for the date in your array
// Add contains to array proto: http://css-tricks.com/snippets/javascript/javascript-array-contains/
var priceResult = [];
for(var i in objArray) {
if(dateArray.contains(objArray[i].date)) priceResult.push(objArray[i].date));
}
console.log('matches:', priceResult);

This function will give you map of all individual arrays in your object array
function getArrayMap(array) {
var map={}
for(var i=0;i<array.length;i++){
var o = array[i];
for(var k in o){
if(!map[k]){
map[k]=[];
}
map[k].push(o[k]);
}
}
return map;
}
you can use it like -
var map = getArrayMap(objArray);
console.log(map["date"]);//date array
console.log(map["price"]);//price array
console.log(map["model"]);//model array

If i am understanding your question correctly, for all the values in array, you want to check the objArr and find the price for each date, and if not found u want to inset null. If this is what you want, then following will help
var found= false;
var list=[];
for(var i=0; i< dateArray.length; i++)
{
for(var j=0; j< objArray.length; j++)
{
if(objArray[j].date == dateArray[i])
{
list.push(objArray[j].price);
found = true;
}
}
if(!found)
{
list.push("null");
}
found = false;
}
alert(list);

(I'm going to call your first array dates rather than array, to avoid confusion.)
There are basically two options:
Loop through your dates array and, for each entry, loop through the objArray looking for a match, and when found add to your priceResult array, or
Build a map from your objArray, then loop through yourdatesarray once, building thepriceResult` array.
Looping and Looping
You can loop through your dates array using forEach, and you can use Array#some to find out whether your objArray contains the date and add to priceResult if so (it's an ES5 feature, but you can polyfill it for really old browsers):
var priceResult = [];
dates.forEach(function(date) {
objArray.some(function(object) {
if (object.date == date) {
priceResult.push(object.price);
return true;
}
});
});
Array#some keeps looping until you return true, which is why we do that when we find the firs tmatch. That's why I say this is "looping and looping," even though we only write one loop, the other is within Array#some.
var dates = ['2014-10-09', '2014-10-10', '2014-10-11', '2014-10-12'];
var objArray = [
{
date: "2014-10-09",
model: "A",
price: "100"
},
{
date: "2014-10-10",
model: "A",
price: "99"
},
{
date: "2014-10-12",
model: "A",
price: "102"
}
];
// Do it
var priceResult = [];
dates.forEach(function(date) {
objArray.some(function(object) {
if (object.date == date) {
priceResult.push(object.price);
return true;
}
});
});
snippet.log(priceResult.join(", "));
<!-- Script provides the `snippet` object, see http://meta.stackexchange.com/a/242144/134069 -->
<script src="http://tjcrowder.github.io/simple-snippets-console/snippet.js"></script>
Mapping and Looping
First, create a map of prices by date:
var prices = {};
objArray.forEach(function(object) {
prices[object.date] = object.price;
});
...then create your results:
var priceResult = [];
dates.forEach(function(date) {
if (prices.hasOwnProperty(date)) {
priceResult.push(prices[date]);
}
});
var dates = ['2014-10-09', '2014-10-10', '2014-10-11', '2014-10-12'];
var objArray = [
{
date: "2014-10-09",
model: "A",
price: "100"
},
{
date: "2014-10-10",
model: "A",
price: "99"
},
{
date: "2014-10-12",
model: "A",
price: "102"
}
];
// Create the map
var prices = {};
objArray.forEach(function(object) {
prices[object.date] = object.price;
});
// Create your results:
var priceResult = [];
dates.forEach(function(date) {
if (prices.hasOwnProperty(date)) {
priceResult.push(prices[date]);
}
});
// Show them
snippet.log(priceResult.join(", "));
<!-- Script provides the `snippet` object, see http://meta.stackexchange.com/a/242144/134069 -->
<script src="http://tjcrowder.github.io/simple-snippets-console/snippet.js"></script>

var dates = ['2014-10-09','2014-10-10','2014-10-11','2014-10-12'];
var objArray = [{date:"2014-10-09", model:"A", price:"100" }, {date:"2014-10-10", model:"A", price:"99" }, {date:"2014-10-12", model:"A", price:"102" }];
var val;
var priceResult = [];
for (var a in dates) {
val = null;
for (var b in objArray) {
if (dates[a] == objArray[b].date) {
val = objArray[b].price;
}
}
priceResult.push(val);
}
var dates = ['2014-10-09', '2014-10-10', '2014-10-11', '2014-10-12'];
var objArray = [{
date: "2014-10-09",
model: "A",
price: "100"
}, {
date: "2014-10-10",
model: "A",
price: "99"
}, {
date: "2014-10-12",
model: "A",
price: "102"
}];
var val;
var priceResult = [];
for (var a in dates) {
val = null;
for (var b in objArray) {
if (dates[a] == objArray[b].date) {
val = objArray[b].price;
}
}
priceResult.push(val);
}
// output result in StackOverflow snippet
document.write(JSON.stringify(priceResult));

Try this:
var temp[]
temp= jQuery.grep(objArray , function (n, i)
{
for(j=0;j<dateArray.lenght+j++ )
if( n.date === dateArray[j])
return n.price;
);

dateArray = ["2014-10-09", "2014-10-10", "2014-10-11", "2014-10-12"];
function ObjectExample(date1,model,price)
{
this.date1 = date1;
this.model = model;
this.price = price;
}
var objArray = [new ObjectExample("2014-10-09","A","100"), new ObjectExample("2014-10-10","A","99"), new ObjectExample("2014-10-12","A","102")];
var i = 0;
var priceDate = new Array();
var count = 0;
while(i < dateArray.length)
{
var j = 0;
while(j < objArray.length)
{
if(dateArray[i] == objArray[j].date1)
{
priceDate[count] = objArray[j].price;
break;
}
else priceDate[count] = "NULL";
j = j + 1;
}
i = i + 1;
count++;
}
document.write(priceDate);

How do I slice an array from an array of object literals?

I have this array, in which each index contains an object literal. All of the object literals have the same properties. Some of the object literals have the same value for a given property, and I want to create a new array containing only those object literals.
My idea is to sort the array, and slice it into a new array...
Here is the array:
var arr = [];
arr[0] =
{
country: "United States",
num: 27
};
arr[1] =
{
country: "Australia",
num: 5
};
arr[2] =
{
country: "United States",
num: 7
};
So, I want to create a new array containing only those objects where the property country is "United States". This is my crazy idea so far, which doesn't work:
function getNewArray(arr)
{
var arr2 = [];
for(var key in arr)
{
for(var i = 0; i < arr.length - 1; i++)
{
if(arr.hasOwnProperty(key) && arr[i].name == arr[i + 1].name)
{
arr2[i] = arr.slice(key);
}
}
}
return arr2;
}
var arr3 = getNewArray(arr).sort();

"I want to create a new array containing only those objects where the property country is "United States""
This is exactly what the Array.filter() method is for:
var filteredArray = arr.filter(function(val, i, a) {
return val.country==="United States";
});
Note that the .filter() method isn't available in IE before version 9, but the MDN page I linked to above shows you exactly how to implement it so reading that page should in itself answer your question.
Note also that in the (non-working) code in the question, your two for loops are basically doing the same thing as each other because they're both iterating over arr, so it doesn't make sense to nest them like that. You shouldn't use a for..in loop on an array, but if you do the key values will be the numeric indexes, it doesn't somehow pick up the properties of the object stored at each index.
EDIT:
"Some of the object literals have the same value for a given property, and I want to create a new array containing only those object literals."
OK, re-reading this I guess you didn't really want to select elements by specifying a country, you wanted to select elements for any country that had duplicate entries? So if there were another three elements that all had "New Zealand" you'd want to select them in addition to the "United States" ones? If so, you could do something like this:
var countryCount = {},
i;
for (i = 0; i < arr.length; i++)
if (countryCount.hasOwnProperty(arr[i].country)
countryCount[arr[i].country]++;
else
countryCount[arr[i].country] = 1;
var filteredArr = arr.filter(function(val, i, a) {
return countryCount[val.country] > 1;
});

var getCountry = function (country) {
var out = [];
for (var i = 0, len = arr.length; i < len; i++)
if (arr[i].country === country) out.push(arr[i]);
return out;
};
Demo: http://jsfiddle.net/YwytD/1/

There is a simpler way of doing this, I think this is what you want
var new_arr = arr.filter(function(obj){ return obj['country'] === 'United States'; })
This will filter your results into new_arr
Of course you can make it better and more generic than just 'United States'
Edit:
Whoops, got your question just now
Answer: Nested Filters :)
function getKeyStuff(key) {
return arr.filter( function(obj) {
var new_arr = arr.filter( function(inner_obj) {
return inner_obj[key] === obj[key];
});
return new_arr.length > 1;
});
}

Here is my solution:
// assuming arr is already set
var num_obj = arr.length;
var obj_by_country = {}, obj;
for (var i = 0; i < num_obj; i++) {
obj = arr[i];
if (!obj_by_country[obj.country]) {
obj_by_country[obj.country] = [];
}
obj_by_country[obj.country].push(obj);
}
// build final array
var final_array = [];
for (i in obj_by_country) {
if (obj_by_country[i].length > 1) {
final_array.push(obj_by_country[i]);
}
}

Can you use JQuery?
var arr = [];
arr[0] = { country: "United States", num: 27 };
arr[1] = { country: "Australia", num: 5 };
arr[2] = { country: "United States", num: 7 };
var newArray = [];
$.each(arr, function(){
if(this.country == "United States")
newArray.push(this);
});

getByKey = function(arr, key, value) {
var results = [];
for(var i = 0; i < arr.length; i++) {
if(arr[i][key] === value) {
results.push(arr[i]);
}
}
return results
}
here's a working example
http://jsfiddle.net/michaelghayes/UyHYz/2/