How to get array key name using jQuery? - javascript

I have an array like this:
var myArray = new Array();
myArray['foo'] = {
Obj: {
key: value
}
};
myArray['bar'] = {
Obj: {
key: value
}
};
When I do console.log(myArray) I just get empty [ ]. And when I try to iterate the array using jQuery's each the function doesn't run.
How can I get the 'foo' and 'bar' parts of the array?
Example code:
console.log(myArray); // [ ]
jQuery.each(myArray, function(key, obj) {
console.log(key); // should be 'foo' following by 'bar'
});
In addition, why does this work:
jQuery.each(myArray[foo], function(obj, values) {
// Why does this work if there are no associative arrays in JS?
});

you can get keys by:
Object.keys(variable name);
it returns array of keys.

You need to define it as an object if you want to access it like that:
var myObj= {};
myObj.foo = ...;
myObj.bar = ...;
Now you can access the properties like myObj["bar"] or myObj.bar
Note:
To loop through all the properties it's wise to add an additional check. This is to prevent you from looping through inherited properties.
for (var key in obj) {
if (obj.hasOwnProperty(key)) {
// Do stuff.
}
}

Array is a collection where each element has an index.
To add element to array you can use push method
myArray.push('someValue');
or set element by index (if length of array < index):
myArray.push('someValue1');
myArray.push('someValue1');
myArray[0] = 'new someValue1';
Note that array is an instance of Object class, so you can add/edit any property of this object:
myArray.foo = '1';
myArray['bar'] = '2';
In this case you will not add new element to array, you defining new properties of object.
And you don't need to create object as Array if you don't wont to use indexes.
To create new object use this code:
var myObj = {};
To get all properties of object see
How to get all properties values of a Javascript Object (without knowing the keys)?

var myArray = {};
myArray['foo'] = { 'key': 'value' }
myArray['bar'] ={ 'key': 'value' }
console.log(myArray)
jQuery.each(myArray['foo'], function(obj, values) {
console.log(obj, values)
});
Demo

With your Array of Objects you could use this function:
var getKeys = function(obj) {
if (!(typeof obj == "object")) return [];
var keys = [];
for (var key in obj) if (obj != null && hasOwnProperty.call(obj, key)) keys.push(key);
return keys;
};
getKeys(myArray) would give you an array of your Keys.
This is basically a cleared up version of underscores _.keys(myArray) function. You should consider using underscore.

// $.each() function can be used to iterate over any collection, whether it is an object or an array.
var myArray = {};
myArray['alfa'] = 0;
myArray['beta'] = 1;
$.each(myArray, function(key, value) {
alert(key);
});
Note: checkout http://api.jquery.com/jQuery.each/ for more information.

Related

JavaScript - Filter <key,value> Object by key

I am looking for a short and efficient way to filter objects by key, I have this kind of data-structure:
{"Key1":[obj1,obj2,obj3], "Key2":[obj4,obj5,obj6]}
Now I want to filter by keys, for example by "Key1":
{"Key1":[obj1,obj2,obj3]}
var object = {"Key1":[1,2,3], "Key2":[4,5,6]};
var key1 = object["Key1"];
console.log(key1);
you can use the .filter js function for filter values inside an object
var keys = {"Key1":[obj1,obj2,obj3], "Key2":[obj4,obj5,obj6]};
var objectToFind;
var keyToSearch = keys.filter(function(objects) {
return objects === objectToFind
});
The keyToSearch is an array with all the objects filter by the objectToFind variable.
Remember, in the line return objects === objectToFind is where you have to should your statement. I hope it can help you.
You can create a new object based on some custom filter criteria by using a combination of Object.keys and the array .reduce method. Note this only works in es6:
var myObject = {"Key1":["a","b","c"], "Key2":["e","f","g"]}
function filterObjectByKey(obj, filterFunc) {
return Object.keys(obj).reduce((newObj, key) => {
if (filterFunc(key)) {
newObj[key] = obj[key];
}
return newObj;
}, {});
}
const filteredObj = filterObjectByKey(myObject, x => x === "Key1")
console.log(filteredObj)
Not sure what exactly are you trying to achieve, but if you want to have a set of keys that you would like to get the data for, you have quite a few options, one is:
var keys = ['alpha', 'bravo'];
var objectToFilterOn = {
alpha: 'a',
bravo: 'b',
charlie: 'c'
};
keys.forEach(function(key) {
console.log(objectToFilterOn[key]);
});

JavaScript create a dictionary - missing key

If I try to create a dictionary this way:
var dict = [];
$.each(objs, function (idx, obj) {
dict[obj.category] = obj;
});
Old elements with the same category are overwritten and each key only has one value, if I do it this way:
var dict = [];
$.each(objs, function (idx, obj) {
dict[obj.category].push(obj);
});
I get an error if the key doesn't exist. How can I solve this problem? I basically want a dictionary which looks like this:
"Category1":{obj1,obj2,obj3},
"Category2":{obj4,obj5,obj6}
first off use an object since arrays have numeric indexing
Create an array if the category key doesn't exist
var dict ={};
$.each(objs, function (idx, obj) {
// if key exists use existing array or assign a new empty array
dict[obj.category] = dict[obj.category] || [] ;
dict[obj.category].push(obj);
});
You could check if the property exists and if not assign an empty array.
Then push the value.
dict[obj.category] = dict[obj.category] || [];
dict[obj.category].push(obj);
It is good to simulate {} for dictionary, but for dictionary logic it will be better to use Maps to work on higher level of abstraction. Check if the object has a key, if not create and assign to it an array, if already has - just push into it.
const map = new Map();
$.each(objs, function (idx, obj) {
if(!map.has(obj.category)) {
map.set(obj.category, []);
}
map.get(obj.category).push(obj);
});
Just use an object.
let dict = {};
dict.Category1 = {};
dict.Category2 = {};
console.log(dict.hasOwnProperty('Category1'), dict.hasOwnProperty('Category3'));
for (item in dict) {
console.log(item, dict[item]);
}

How to dynamically change the key names of object properties in an array

I have an array of objects, like so:
arr = [{"timeslot":"6am7am","AVG(Monday)":10,"AVG(Tuesday)":11,"AVG(Wednesday)":7}]
Each object will always contain the "timeslot" property, and can contain any combination of the day-of-the-week properties, Monday through Sunday. Each day of the week may only be represented once in a single object.
I want to alter each object: specifically, the key names of the day-of-the-week properties only (the "timeslot" property will be unchanged"), to get an array like so:
newArr = [{"timeslot":"6am7am","Monday":10,"Tuesday":11,"Wednesday":7}]
My slightly unreadable solution works:
// Iterate the array of objects
results.forEach(function(o) {
// Iterate the object's properties
Object.keys(o).forEach(function(k) {
if(k.includes("AVG")) {
var len = k.length;
var pos = len - 1;
var newKey = k.slice(4, pos); // Extract the day of the week from the key name
o[newKey] = o[k]; // Create the new property with the same value and the new key-name
delete o[k]; // Delete the original property
}
});
});
How can I improve this solution?
Instead of mutating the original array by adding and removing keys from each object, Array#map the array into a new array, and recreate the objects using Array#reduce:
var arr = [{"timeslot":"6am7am","AVG(Monday)":10,"AVG(Tuesday)":11,"AVG(Wednesday)":7}];
var result = arr.map(function(obj) {
return Object.keys(obj).reduce(function(r, key) {
var k = key.includes('AVG') ? key.slice(4, -1) : key;
r[k] = obj[key];
return r;
}, {});
});
console.log(result);

JSON.stringify serializes to [[]]

If I create a JavaScript object like:
var lst = [];
var row = [];
row.Col1 = 'val1';
row.Col2 = 'val2';
lst.push(row);
And then convert it to a string:
JSON.stringify(lst);
The result is an object containing an empty object:
[[]]
I would expect it to serialize like:
[[Col1 : 'val1', Col2: 'val2']]
Why do the inner objects properties not serialize?
Code snippet at JSFiddle.
Because row is an array, not an object. Change it to:
var row = {};
This creates an object literal. Your code will then result in an array of objects (containing a single object):
[{"Col1":"val1","Col2":"val2"}]
Update
To see what really happens, you can look at json2.js on GitHub. This is a (heavily reduced) snippet from the str function (called by JSON.stringify):
if (Object.prototype.toString.apply(value) === '[object Array]') {
//...
length = value.length;
for (i = 0; i < length; i += 1) {
partial[i] = str(i, value) || 'null';
}
//...
}
//...
for (k in value) {
if (Object.prototype.hasOwnProperty.call(value, k)) {
//...
}
//...
}
//...
Notice that arrays are iterated over with a normal for loop, which only enumerates the array elements. Objects are iterated with a for...in loop, with a hasOwnProperty test to make sure the proeprty actually belongs to this object.
You use your inner array like an object, so make it an object instead of an array.
var lst = [];
var row = {};
row.Col1 = 'val1';
row.Col2 = 'val2';
lst.push(row);
or use it as an array
var lst = [];
var row = {};
row.push( 'val1' );
row.push( 'val2' );
lst.push(row);
You want row to be a dictionary, not a vector. Define it like this:
var row = {};
Since an array is a datatype in JSON, actual instances of Array are stringified differently than other object types.
If a JavaScript Array instance got stringified with its non-numeric keys intact, it couldn't be represented by the [ ... ] JSON array syntax.
For instance, [ "Col1": "val1"] would be invalid, because JSON arrays can't have explicit keys.
{"Col1": "val1"} would be valid - but it's not an array.
And you certainly can't mix'n'match and get { "Col1": "val1", 1, 2, 3 ] or something.
By the way, this works fine:
var lst = [];
var row = {};
row.Col1 = 'val1';
row.Col2 = 'val2';
lst.push(row);
alert(JSON.stringify(lst));​

Getting the first index of an object

Consider:
var object = {
foo: {},
bar: {},
baz: {}
}
How would I do this:
var first = object[0];
console.log(first);
Obviously, that doesn’t work because the first index is named foo,
not 0.
console.log(object['foo']);
works, but I don’t know it’s named foo. It could be named anything. I just want the first.
Just for fun this works in JS 1.8.5
var obj = {a: 1, b: 2, c: 3};
Object.keys(obj)[0]; // "a"
This matches the same order that you would see doing
for (o in obj) { ... }
If you want something concise try:
for (first in obj) break;
alert(first);
wrapped as a function:
function first(obj) {
for (var a in obj) return a;
}
they're not really ordered, but you can do:
var first;
for (var i in obj) {
if (obj.hasOwnProperty(i) && typeof(i) !== 'function') {
first = obj[i];
break;
}
}
the .hasOwnProperty() is important to ignore prototyped objects.
This will not give you the first one as javascript objects are unordered, however this is fine in some cases.
myObject[Object.keys(myObject)[0]]
If the order of the objects is significant, you should revise your JSON schema to store the objects in an array:
[
{"name":"foo", ...},
{"name":"bar", ...},
{"name":"baz", ...}
]
or maybe:
[
["foo", {}],
["bar", {}],
["baz", {}]
]
As Ben Alpert points out, properties of Javascript objects are unordered, and your code is broken if you expect them to enumerate in the same order that they are specified in the object literal—there is no "first" property.
for first key of object you can use
console.log(Object.keys(object)[0]);//print key's name
for value
console.log(object[Object.keys(object)[0]]);//print key's value
There is no way to get the first element, seeing as "hashes" (objects) in JavaScript have unordered properties. Your best bet is to store the keys in an array:
var keys = ["foo", "bar", "baz"];
Then use that to get the proper value:
object[keys[0]]
ES6
const [first] = Object.keys(obj)
Using underscore you can use _.pairs to get the first object entry as a key value pair as follows:
_.pairs(obj)[0]
Then the key would be available with a further [0] subscript, the value with [1]
I had the same problem yesterday. I solved it like this:
var obj = {
foo:{},
bar:{},
baz:{}
},
first = null,
key = null;
for (var key in obj) {
first = obj[key];
if(typeof(first) !== 'function') {
break;
}
}
// first is the first enumerated property, and key it's corresponding key.
Not the most elegant solution, and I am pretty sure that it may yield different results in different browsers (i.e. the specs says that enumeration is not required to enumerate the properties in the same order as they were defined). However, I only had a single property in my object so that was a non-issue. I just needed the first key.
You could do something like this:
var object = {
foo:{a:'first'},
bar:{},
baz:{}
}
function getAttributeByIndex(obj, index){
var i = 0;
for (var attr in obj){
if (index === i){
return obj[attr];
}
i++;
}
return null;
}
var first = getAttributeByIndex(object, 0); // returns the value of the
// first (0 index) attribute
// of the object ( {a:'first'} )
To get the first key of your object
const myObject = {
'foo1': { name: 'myNam1' },
'foo2': { name: 'myNam2' }
}
const result = Object.keys(myObject)[0];
// result will return 'foo1'
Based on CMS answer. I don't get the value directly, instead I take the key at its index and use this to get the value:
Object.keyAt = function(obj, index) {
var i = 0;
for (var key in obj) {
if ((index || 0) === i++) return key;
}
};
var obj = {
foo: '1st',
bar: '2nd',
baz: '3rd'
};
var key = Object.keyAt(obj, 1);
var val = obj[key];
console.log(key); // => 'bar'
console.log(val); // => '2nd'
My solution:
Object.prototype.__index = function(index)
{
var i = -1;
for (var key in this)
{
if (this.hasOwnProperty(key) && typeof(this[key])!=='function')
++i;
if (i >= index)
return this[key];
}
return null;
}
aObj = {'jack':3, 'peter':4, '5':'col', 'kk':function(){alert('hell');}, 'till':'ding'};
alert(aObj.__index(4));

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