Javascript Looping through objects - javascript

var a = {
element:'input',
parent:'div1',
name:'inp',
type:'text',
value:'aa'
}
I want to loop through this object starting from name attribute using for in loop
But I am unable to do this using for in loop
is there any way to loop through the object starting from the name attribute

Old way:
for (var key in a) {
if (a.hasOwnProperty(key)) {
// todo something with a[key]
}
}
ES6 way:
Object.keys(a).forEach(function(key) {
// todo something with a[key]
});

for(var prop in a) {
console.log(a[prop]);
}

You could do something like this:
var keys = Object.keys(a);
var length = keys.length;
var startAt = keys.indexOf("name");
for(var i = 0; i < length ; i++) {
var prop = keys[(i+startAt)%length];
console.log(prop, a[prop]);
}
Or:
var keys = Object.keys(a).sort(function(a,b){ return a !== "name" });
for(var i = 0; i < keys.length; i++) {
var prop = keys[i];
console.log(prop, a[prop]);
}
Or:
var keys = Object.keys(a);
var idx = keys.indexOf("name");
if(idx > 0) {
var tmp = keys[0];
keys[0] = keys[idx];
keys[idx] = tmp;
}
for(var i = 0; i < keys.length; i++) {
var prop = keys[i];
console.log(prop, a[prop]);
}
But keep in mind that objects are unordered lists even though most browsers keep object properties in the order in which they were added.

I believe you can do it as follows:
function loopFromIndex(input, index) {
var started = false;
for (var property in input) {
started = started || (index === property);
if (started) {
//process iteration
}
}
}
You are still looping the whole property set, but when you encounter the given index, you will start the real loop.

Related

How do I build an object counting occurrences in an Array in JavaScript?

I want to count how often a number in an Array occurs. For example, in Python I can use Collections.Counter to create a dictionary of how frequently an item occurs in a list.
This is as far as I've gotten in JavaScript:
var array = [1,4,4,5,5,7];
var obj = {};
for (var i=0; i < array.length; i++) {
/* obj[array[i]] = +=1 */ <= pseudo code
}
How can I create this frequency counter object?
Close but you can't increment undefined so you need to set initial value if it doesn't exist
var array = [1,4,4,5,5,7];
var obj = {};
for (var i=0; i < array.length; i++) {
obj[array[i]] = (obj[array[i]] || 0) +1 ;
}
You were almost there. See below code:
var array = [1,4,4,5,5,7];
var obj = {};
for (var i=0; i < array.length; i++) {
obj[array[i]] = (obj[array[i]] || 0 ) +1;
}
console.log(obj);
Create an object and check if that specific key exist.If exist then increase it's value by 1
var array = [1, 4, 4, 5, 5, 7];
var obj = {};
for (var i = 0; i < array.length; i++) {
if (obj.hasOwnProperty(array[i])) {
obj[array[i]] += 1;
} else {
obj[array[i]] = 1;
}
}
console.log(obj)
You can use the ? : ternary operator to set initial value as 1 and then increment it on subsequent matches.
var array = [1,4,4,5,5,7];
var obj = {};
for (var i=0; i < array.length; i++) {
obj[array[i]] = obj[array[i]]?obj[array[i]]+1:1;
}
console.log(obj);
If the array is always going to be same, and you are going to check frequency of multiple items in the same array without it it being modified, #JohanP's answer is good.
But if you are only going to check frequency of only one item, or the array can change, creating the object is nothing but extra overhead.
In that case, you can do something like this:
const getItemFrequency = function(array, item) {
return array.filter(i => i === item).length;
}
var array = [1,4,4,5,5,7];
console.log(getItemFrequency(array, 4));
Concise logic written as proper function:
function countArrayItemFrequecy(array) {
const length = array.length;
const map = {};
for ( let i = 0; i < length; i++ ) {
let currentItem = array[i];
if (typeof map[currentItem] !== 'undefined' ) {
map[currentItem]++
} else {
map[currentItem] = 1
}
}
return map;
}
You need to make sure to assign default value to your frequency object for the first occurrence of the item. As a shortcut you can use ternary operator
var array = [1,4,4,5,5,7];
var obj = {};
for (var i=0; i < array.length; i++) {
obj[array[i]] = obj[array[i]] ? obj[array[i]]++ : 1;
}
which is the same as:
var array = [1,4,4,5,5,7];
var obj = {};
for (var i=0; i < array.length; i++) {
if (obj[array[i]]) {
obj[array[i]]++;
} else {
obj[array[i]] = 1;
}
}
You can use Object.assign: below clones map and then increments/adds the counter. These are pure (no side effects/param reassignment), single-purpose functions.
addToMap does the same thing as { ...map, map[e]: [e]: (map[e] || 0) + 1 }, but that requires babel.
const addToMap = (map, e) => Object.assign({}, map, { [e]: (map[e] || 0) + 1 });
const buildMap = a => a.reduce(addToMap, {});
Using Array.reduce:
arr.reduce(function (acc, item) {
acc[item] = (acc[item] || 0) + 1;
return acc;
}, {});
Example:
var arr = [1,1,2,4,1,4];
var counts = arr.reduce(function (acc, item) {
acc[item] = (acc[item] || 0) + 1;
return acc;
}, {});
console.log(counts);

javascript array - increment value at given key

I have a dynamic array and I am trying to increment the value by 1 if the key exists in the array. According to my debug it is incrementing the key and and creating a second key/value pair.
A snippet of my code:
for (var i = 0; i < choices.length; i++) {
console.log(choices[i]);
if (choices[i].YearTermId == 1) {
if (!lookup(firstChoice, choices[i].FirstChoiceOptionId)) {
firstChoice.push({
key: choices[i].FirstChoiceOptionId,
value: 1
});
} else {
firstChoice[choices[i].FirstChoiceOptionId] = firstChoice[choices[i].FirstChoiceOptionId] + 1;
}
more if/else..
function lookup( arr, name ) {
for(var i = 0, len = arr.length; i < len; i++) {
if( arr[ i ].key === name )
return true;
}
return false;
}
You're using an array where you should be using an object. If you use an object, your code can be rewritten as:
var firstChoice = {};
for (var i = 0; i < choices.length; i++) {
var firstChoiceOptionId = choices[i].FirstChoiceOptionId;
if (choices[i].YearTermId == 1) {
firstChoice[firstChoiceOptionId] = firstChoice[firstChoiceOptionId]
? firstChoice[firstChoiceOptionId] + 1
: 1;
/* ... */
}
}
If you need the data as an array afterwards, just map it:
var firstChoiceArray = Object.keys(firstChoice).map(function(key) {
return {
key: key,
value: firstChoice[key]
};
});
Conversely, if you have an input array and want to convert it to an object for manipulation, reduce it:
var firstChoice = firstChoiceArray.reduce(function(result, current) {
result[current.key] = current.value;
return result;
}, {});
I think you should increment value key, like:
firstChoice[choices[i].FirstChoiceOptionId].value ++;
And I would like to rewrite this code to:
var firstChoice = {};
for (var i = 0; i < choices.length; i++) {
if (choices[i].YearTermId == 1) {
if (!firstChoice[choices[i].FirstChoiceOptionId]) {
firstChoice[choices[i].FirstChoiceOptionId] = 0;
}
firstChoice[choices[i].FirstChoiceOptionId]++;
}
}
console.log(firstChoice);
Try with Array.map:
Example:
var a = [{key:"ab","value":1},{key:"cd","value":1},{key:"ef","value":1}];
a.map(function(item){if(item.key == this){item.value++}}, "cd");
So, a[1] will have value 2 after that.

How can I return the longest string in an array—even if the array contains items that are not strings?

Let's say I'm writing a function like so:
function longestString (someArray) {
// code
}
If someArray = ['word','longer phrase',['a','b','c'],1234567891011121314151617], I would want the function to only return the longest string in the array and ignore the integers and other arrays that may also lie within it. I tried this:
function longestString (someArray) {
return someArray.sort(function (a, b) { return b.length - a.length; })[0];
}
It didn't work, and I am now stuck. :/
Filter only string element and do it
function longestString (someArray) {
return someArray
.filter(function(a){ return typeof(a)=='string' })
.sort(function (a, b) { return b.length - a.length; })[0];
}
Try this:
function longestString(someArray) {
var result = "";
for (var i = 0; i < someArray.length; i++) {
if ((typeof someArray[i] === "string") && (someArray[i].length > result.length)) {
result = someArray[i];
}
}
return result;
}
try to do :
function longestString (someArray) {
$longest_string = '';
foreach ($someArray as $value)
{
$current_length = strlen($longest_string);
if(strlen($value) > $current_length ) $longest_string = $value;
}
return $longest_string;
}
Try this.
var a = ['word', 'longer phrase', ['a', 'b', 'c'], 1234567891011121314151617];
returnLongestString(a);
function returnLongestString(arr) {
var longestString = '';
for (var i = 0; i < arr.length; i++) {
if (typeof arr[i] == "string" && arr[i].length > longestString.length) {
longestString = arr[i];
}
};
return longestString;
}
When I saw this question, it had 0 answers, when I finished writing and testing my function, there were five. But this is my approach:
The key here is to first filter only the strings. Then, list all the lengths on an array. Then using that array you can get a match on the bigger one.
function longestString (someArray) {
//we only need strings, so first we will filter all the data
var stringsOnly = [];
for (var i = 0; i < someArray.length; i++) {
if(typeof(someArray[i]) === 'string'){
stringsOnly.push(someArray[i]);
}
};
//Now with an array of just strings, we can get their indivial lenghts
var stringLengths = [];
for (var i = 0; i < stringsOnly.length; i++) {
var currentString = stringsOnly[i];
stringLengths.push(currentString.length);
};
//Get the max length
var maxLength = Math.max.apply(Math,stringLengths);
//get a string wich length equals to maxLength
for (var i = 0; i < stringsOnly.length; i++) {
var theString = stringsOnly[i];
if(theString.length === maxLength){return theString};
};
}
This function will return the largest string. If more than one string have the same length, It will return the first one. However, if you want to get various strings, you could make some little modificationson the function above:
function multipleLongestString (someArray) {
//we only need strings, so first we will filter all the data
var stringsOnly = [];
for (var i = 0; i < someArray.length; i++) {
if(typeof(someArray[i]) === 'string'){
stringsOnly.push(someArray[i]);
}
};
//Now with an array of just strings, we can get their indivial lenghts
var stringLengths = [];
for (var i = 0; i < stringsOnly.length; i++) {
var currentString = stringsOnly[i];
stringLengths.push(currentString.length);
};
//Get the max length
var maxLength = Math.max.apply(Math,stringLengths);
//modification here
longests = [];
//get a string wich length equals to maxLength
for (var i = 0; i < stringsOnly.length; i++) {
var theString = stringsOnly[i];
if(theString.length === maxLength){longests.push(theString)};
};
return longests;
}
That is an extra that may help you later. But if you just want the largest one, use the first function. I hope that my answer is relevant.
:)
Heres my approach at it. Really all you want to know is if the phrase is longer than the previous and if its a string.
jsFiddle here.
var someArray = ['word','longer phrase',['a','b','c'],1234567891011121314151617]
var longestString = function(arr) {
var longest = "";
for (var i = 0; i < arr.length; i++) {
var value = arr[i];
if (typeof value === "string") {
longest = arr[i];
}
}
alert(longest);
}
longestString(someArray);

Copying array of objects into another array is it reference type in JQuery

I have a array of objects TransactionVModel.FiltersList[].
When I copy this array to another array fltrList[] and if I modify any of the object in array fltrList will it get reflect in Array TransactionVModel.FiltersList in JQuery ? For better clarity below is my example. As per me since it is a reference type it should update array TransactionVModel.FiltersList as well but in my scenario it is not happening, can I know why it is not happening ?
TransactionVModel.FiltersList is declared as ko.observableArray(); in my code.
function UpdateSelectedFilters(data) {
var fltrList = [];
fltrList = TransactionVModel.FiltersList();
for (var i = 0; i < data.length ; i++) {
var index = fltrList.indexOf(data[i]);
if (index != -1) {
var fltrObj = fltrList[index];
var fltrValArr = [];
fltrValArr = data.valueItems;
for (var j = 0; j < fltrValArr.length; j++) {
if (fltrValArr[j].IsSelected == true) {
if (fltrObj.indexOf(fltrValArr[j]) != -1) {
var selectedVal = fltrObj[fltrObj.indexOf(fltrValArr[j])];
selectedVal.IsSelected = true;
}
}
}
}
}
In my scenario I am updating selectedVal.IsSelected property but it is not reflecting the observableArray TransactionVModel.FiltersList.
You need to tell knockout that your array has changed with valueHasMutated:
function UpdateSelectedFilters(data) {
var fltrList = [];
fltrList = TransactionVModel.FiltersList();
//...
TransactionVModel.FiltersList.valueHasMutated();
}

How do I merge a list of results into a compacted object with totals

I'm looping through a set of inputs. I need to tally up the grouped totals.
var compoundedArray = new Array();
holder.find(".dataset input").each(function(index) {
var val = $(this).val();
var dataType = $(this).data("type");
var localObj = {};
localObj[dataType] = val;
compoundedArray.push(localObj);
});
I have an object like this
[
{
"growth":30
},
{
"growth": 40
},
{
"other": 20
}
]
how do I loop through the object to produce something like
[
{
"growth": 70
},
{
"other": 20
}
]
if I looped over the initial array object
for (var i = 0; i < compoundedArray.length; i++) {
console.log(compoundedArray[i]);
}
how would I go about checking to ensure I don't have duplicates - and that I can tally up the results?
I think your selection of data structure is a bit too complicated. Try something like.
var compoundedObject = {};
holder.find(".dataset input").each(function(index) {
var val = $(this).val();
var dataType = $(this).data("type");
//Assuming all values are integers and can be summed:
if( compoundedObject.hasOwnProperty(dataType) )
{
compoundedObject[dataType] += val;
}
else
{
compoundedObject[dataType] = val;
}
});
You will end up with an object, not an array though.
var add=function (a,b){ a=a||0; b=b||0; return a+b};
var input=[ {growth:30},{growth:40},{other:20} ],output=[],temp={};
$.each(input,function(i,o){
var n;
for(i in o)
{n=i;break}
temp[n]=add(temp[n],o[n]);
});
$.each(temp,function(i,o){
var k={};
k[i]=o;
output.push(k)
});
find output at output variable.
Do not post much specific question, It might not help others.
This works. And it's pure javascript.
var totals = {};
for (var i = 0; i < compoundedArray.length; i++) {
var item = compoundedArray[i];
for (var key in item) {
totals[key] = (totals[key] || 0) + item[key]
}
};
You can loop trough an Object with a for loop.
If you want to delete an item simply set it to null.
Example:
for(var i in compoundedArray){
for(var j in compoundedArray){
if(i == j){
compoundedArray[i] += compoundedArray[j];
compoundedArray[j] = null;
}
}
}
You can do the following:
var totals = [], tmp = {};
for (var i = 0; i < compoundedArray.length; i++) {
var obj = compoundedArray[i];
for (var j in obj) {
tmp[j] = tmp[j] || 0;
tmp[j] += obj[j];
}
}
for(var k in tmp) {
var obj = {};
obj[k] = tmp[k];
totals.push(obj);
}
See this working demo

Categories

Resources