How do I define an associative array? - javascript

I want to define what I understand is an associative array (or maybe an object) such that I have entries like the following:
"Bath" = [1,2,5,5,13,21]
"London" = [4,7,13,25]
I've tried the following:
var xref = new Object;
xref = [];
obj3 = {
offices: []
};
xref.push(obj3);
Then cycling through my data with
xref[name].offices.push(number);
But I get "TypeError: xref[name] is undefined". What am I doing wrong ?

Use an object like you do with obj3:
var xref = {};
xref.obj3 = obj3;
var name = 'obj3';
xref[name].offices.push(number);

var obj = {
arr : [],
}
var name = "vinoth";
obj.arr.push(name);
console.log(obj.arr.length);
console.log(obj.arr[0]);
obj.prop = "Vijay";
console.log(obj.prop);
You can use an object literal.

I realised that all I really wanted was a 2 dimensional array with the first dimension being the key (ie. "BATH", "LONDON") and the second being the list of cross-references (ie. 1,2,5,5,13,21) - so I don't need to understand the Object route yet ! The other suggestions may well work and be "purer" but the 2 dimensional array is easier for my old-fashioned brain to work with.
So I did the following:
var xref = [];
// go through source arrays
for (i = 0; i < offices.length; i++) {
for (j = 0; j < offices[i].rel.length; j++) {
// Check if town already exists, if not create array, then push index
if (xref[offices[i].rel[j].town] === undefined) {
xref[offices[i].rel[j].town] = [];
alert('undefined so created '+offices[i].rel[j].town);
};
xref[offices[i].rel[j].town].push(i); // Add index to town list
};
};
I believe from reading other posts that I would have problems if any of the 'offices[i].rel[j].town' were set to undefined but the data doesn't have this possibility.
Now I can access a cross-reference list by doing something like:
townlist = "";
for (i = 0; i < xref["BATH"].length; i++) {
townlist += offices[xref["BATH"][i]].name+' ';
};
alert(townlist);

Related

Create nested Javascript Object dynamically

I have got a . (dot) separated string, from which I want to create nested JSON object. The length of the string is not fixed. For example,
var string = 'a.b.c.d';
Then my JSON object should be as following:
a: {
b: {
c:{
d: {
//Some properties here.
}
}
}
}
I've tried following code:
var packageName = "a.b.c.d"
var splitted = packageName.split('.');
var json = {};
for(var i=0;i<splitted.length-1;i++){
json[splitted[i]] = splitted[i+1];
}
But this returns
{
a: 'b',
b: 'c',
c: 'd'
}
But this is not what I want. I've also searched on google and found similar questions, but no solutions answer my problem. For example this.
A good use case for reduce
packageName = "a.b.c.d";
initProps = {hi: 'there'};
obj = packageName.split('.').reduceRight((o, x) => ({[x]: o}), initProps);
console.log(JSON.stringify(obj))
If you find loops easier to work with, a loop could be written concisely as
result = {};
ptr = result;
for (let prop of packageName.split('.'))
ptr = ptr[prop] = {};
You need to create a new object each time and attribute it to the last object created. And it goes until splitted.length, not splitted.length - 1, because you're using <, not <=.
var packageName = "a.b.c.d";
var splitted = packageName.split('.');
var json = {};
var current = json;
for (var i = 0; i < splitted.length; i++) {
current[splitted[i]] = {};
current = current[splitted[i]];
}
console.log(json);
You may use the last splittted part as property for some payload.
I suggest to keep the object reference and use a temporary variable for aceessing an creating a new property, if necessary.
Please avoid the use of JSON for not stringified objects.
var packageName = "a.b.c.d",
splitted = packageName.split('.'),
result = {},
temp = result,
i;
for (i = 0; i < splitted.length - 1; i++) {
temp[splitted[i]] = temp[splitted[i]] || {};
temp = temp[splitted[i]];
}
temp[splitted[i]] = { some: 'data' };
console.log(result);

Algorithm to sort an array in JS

I have an array
var arr= [
["PROPRI","PORVEC"],
["AJATRN","PROPRI"],
["BASMON","CALVI"],
["GHICIA","FOLELI"],
["FOLELI","BASMON"],
["PORVEC","GHICIA"]
] ;
And I'm trying to sort the array by making the second element equal to the first element of the next, like below:
arr = [
["AJATRN","PROPRI"],
["PROPRI","PORVEC"],
["PORVEC","GHICIA"],
["GHICIA","FOLELI"],
["FOLELI","BASMON"],
["BASMON","CALVI"]
]
The context is : these are somes sites with coordinates, I want to identify the order passed,
For exemple, I have [A,B] [C,D] [B,C] then I know the path is A B C D
I finally have one solution
var rs =[];
rs[0]=arr[0];
var hasAdded=false;
for (var i = 1; i < arr.length; i++) {
hasAdded=false;
console.log("i",i);
for (var j = 0, len=rs.length; j < len; j++) {
console.log("j",j);
console.log("len",len);
if(arr[i][1]===rs[j][0]){
rs.splice(j,0,arr[i]);
hasAdded=true;
console.log("hasAdded",hasAdded);
}
if(arr[i][0]===rs[j][1]){
rs.splice(j+1,0,arr[i]);
hasAdded=true;
console.log("hasAdded",hasAdded);
}
}
if(hasAdded===false) {
arr.push(arr[i]);
console.log("ARR length",arr.length);
}
}
But it's not perfect, when it's a circle like [A,B] [B,C] [C,D] [D,A]
I can't get the except answer
So I really hope this is what you like to achieve so have a look at this simple js code:
var vector = [
["PROPRI,PORVEC"],
["AJATRN,PROPRI"],
["BASMON,CALVI"],
["GHICIA,FOLELI"],
["FOLELI,BASMON"],
["PORVEC,GHICIA"]
]
function sort(vector) {
var result = []
for (var i = 1; i < vector.length; i++) result.push(vector[i])
result.push(vector[0])
return (result)
}
var res = sort(vector)
console.log(res)
Note: Of course this result could be easily achieved using map but because of your question I'm quite sure this will just confuse you. So have a look at the code done with a for loop :)
You can create an object lookup based on the first value of your array. Using this lookup, you can get the first key and then start adding value to your result. Once you add a value in the array, remove the value corresponding to that key, if the key has no element in its array delete its key. Continue this process as long as you have keys in your object lookup.
var vector = [["PROPRI", "PORVEC"],["AJATRN", "PROPRI"],["BASMON", "CALVI"],["GHICIA", "FOLELI"],["FOLELI", "BASMON"],["PORVEC", "GHICIA"]],
lookup = vector.reduce((r,a) => {
r[a[0]] = r[a[0]] || [];
r[a[0]].push(a);
return r;
}, {});
var current = Object.keys(lookup).sort()[0];
var sorted = [];
while(Object.keys(lookup).length > 0) {
if(lookup[current] && lookup[current].length) {
var first = lookup[current].shift();
sorted.push(first);
current = first[1];
} else {
delete lookup[current];
current = Object.keys(lookup).sort()[0];
}
}
console.log(sorted);

Javascript multi-dimension array initialization

I'm looking for the best way to initialize multi-dimensional arrays in Javascript. I'm much more familiar with PHP where I'm not obliged to declare arrays or dimensions before feeding it with values.
Basically what I tried to do is create an array with the following format
catalogue[i]["name"]="a name";
catalogue[i]["description"]="a description";
...etc...
If I do the following:
var catalogue = new Array();
for (i=0; i<otherarray.length;i++)
{
catalogue[i]['name']=otherarray[i];
}
Catalogue is undefined, I also tried with catalogue[i].name but same issue. If I only assign a simple value like catalogue[i]=2, it works but that's not what I'm looking for. I couldn't find a working example of what I'm looking for.
Do I need to initialize every possible dimension of an array before being able to feed it with new values?
Thanks
Laurent
var catalogue = new Array();
for (i = 0; i < otherarray.length; i++) {
catalogue[i] = {};
catalogue[i]['name'] = otherarray[i];
}
Or
var catalogue = new Array();
for (i = 0; i < otherarray.length; i++) {
catalogue.push({"name":otherarray[i]});
}
Put this in your loop to create the object you want to store the values in:
catalogue[i] = {}; OR catalogue.push({});
Your code would be like this then:
var catalogue = new Array();
for (i=0; i<otherarray.length;i++)
{
catalogue[i] = {}; // initialization
catalogue[i]['name']=otherarray[i];
}
Note that you can initialize and assign a value in the same line:
var catalogue = new Array();
for (i=0; i<otherarray.length;i++)
{
catalogue[i] = {
name: otherarray[i],
otherKey: 'otherValue' // list all of your keys and values
};
}
If you want string keys in your array in Javascript you have to declare an Object. The catalogue variable itself is an array but each element inside that array is an object with the two keys "name" and "description". For example this code works :
var c = [1,2,3,4,5];
var n = ['one', 'two', 'three', 'four', 'five'];
var cat = [];
for (i = 0; i < c.length; i++)
{
cat[i] = {
name : n[i],
value: c[i]
};
}
now if you console.dir(cat); it outputs this result :
Array[5]
-> 0 : Object
name: "one"
value: 1
-> 1 : Object
name: "two"
value: 2
...

jQuery $.each with sorted object keys [duplicate]

Let's say I have a Javascript associative array (a.k.a. hash, a.k.a. dictionary):
var a = new Array();
a['b'] = 1;
a['z'] = 1;
a['a'] = 1;
How can I iterate over the keys in sorted order? If it helps simplify things, I don't even need the values (they're all just the number 1).
You can use the Object.keys built-in method:
var sorted_keys = Object.keys(a).sort()
(Note: this does not work in very old browsers not supporting EcmaScript5, notably IE6, 7 and 8. For detailed up-to-date statistics, see this table)
You cannot iterate over them directly, but you can find all the keys and then just sort them.
var a = new Array();
a['b'] = 1;
a['z'] = 1;
a['a'] = 1;
function keys(obj)
{
var keys = [];
for(var key in obj)
{
if(obj.hasOwnProperty(key))
{
keys.push(key);
}
}
return keys;
}
keys(a).sort(); // ["a", "b", "z"]
However there is no need to make the variable 'a' an array. You are really just using it as an object and should create it like this:
var a = {};
a["key"] = "value";
you could even prototype it onto object:
Object.prototype.iterateSorted = function(worker)
{
var keys = [];
for (var key in this)
{
if (this.hasOwnProperty(key))
keys.push(key);
}
keys.sort();
for (var i = 0; i < keys.length; i++)
{
worker(this[ keys[i] ]);
}
}
and the usage:
var myObj = { a:1, b:2 };
myObj.iterateSorted(function(value)
{
alert(value);
}
I agree with Swingley's answer, and I think it is an important point a lot of these more elaborate solutions are missing. If you are only concerned with the keys in the associative array and all the values are '1', then simply store the 'keys' as values in an array.
Instead of:
var a = { b:1, z:1, a:1 };
// relatively elaborate code to retrieve the keys and sort them
Use:
var a = [ 'b', 'z', 'a' ];
alert(a.sort());
The one drawback to this is that you can not determine whether a specific key is set as easily. See this answer to javascript function inArray for an answer to that problem. One issue with the solution presented is that a.hasValue('key') is going to be slightly slower than a['key']. That may or may not matter in your code.
There's no concise way to directly manipulate the "keys" of a Javascript object. It's not really designed for that. Do you have the freedom to put your data in something better than a regular object (or an Array, as your sample code suggests)?
If so, and if your question could be rephrased as "What dictionary-like object should I use if I want to iterate over the keys in sorted order?" then you might develop an object like this:
var a = {
keys : new Array(),
hash : new Object(),
set : function(key, value) {
if (typeof(this.hash[key]) == "undefined") { this.keys.push(key); }
this.hash[key] = value;
},
get : function(key) {
return this.hash[key];
},
getSortedKeys : function() {
this.keys.sort();
return this.keys;
}
};
// sample use
a.set('b',1);
a.set('z',1);
a.set('a',1);
var sortedKeys = a.getSortedKeys();
for (var i in sortedKeys) { print(sortedKeys[i]); }
If you have no control over the fact that the data is in a regular object, this utility would convert the regular object to your fully-functional dictionary:
a.importObject = function(object) {
for (var i in object) { this.set(i, object); }
};
This was a object definition (instead of a reusable constructor function) for simplicity; edit at will.
Get the keys in the first for loop, sort it, use the sorted result in the 2nd for loop.
var a = new Array();
a['b'] = 1;
a['z'] = 1;
a['a'] = 1;
var b = [];
for (k in a) b.push(k);
b.sort();
for (var i = 0; i < b.length; ++i) alert(b[i]);
You can use the keys function from the underscore.js library to get the keys, then the sort() array method to sort them:
var sortedKeys = _.keys(dict).sort();
The keys function in the underscore's source code:
// Retrieve the names of an object's properties.
// Delegates to **ECMAScript 5**'s native `Object.keys`
_.keys = nativeKeys || function(obj) {
if (obj !== Object(obj)) throw new TypeError('Invalid object');
var keys = [];
for (var key in obj) if (_.has(obj, key)) keys.push(key);
return keys;
};
// Shortcut function for checking if an object has a given property directly
// on itself (in other words, not on a prototype).
_.has = function(obj, key) {
return hasOwnProperty.call(obj, key);
};
<script type="text/javascript">
var a = {
b:1,
z:1,
a:1
}; // your JS Object
var keys = [];
for (key in a) {
keys.push(key);
}
keys.sort();
var i = 0;
var keyslen = keys.length;
var str = '';
//SORTED KEY ITERATION
while (i < keyslen) {
str += keys[i] + '=>' + a[keys[i]] + '\n';
++i;
}
alert(str);
/*RESULT:
a=>1
b=>1
z=>1
*/
</script>
var a = new Array();
a['b'] = 1;
a['z'] = 1;
a['a'] = 1;
var keys=Object.keys(a).sort();
for(var i=0,key=keys[0];i<keys.length;key=keys[++i]){
document.write(key+' : '+a[key]+'<br>');
}
I really like #luke-schafer's prototype idea, but also hear what he is saying about the issues with prototypes. What about using a simple function?
function sortKeysAndDo( obj, worker ) {
var keys = Object.keys(obj);
keys.sort();
for (var i = 0; i < keys.length; i++) {
worker(keys[i], obj[keys[i]]);
}
}
function show( key, value ) {
document.write( key + ' : ' + value +'<br>' );
}
var a = new Array();
a['b'] = 1;
a['z'] = 1;
a['a'] = 1;
sortKeysAndDo( a, show);
var my_object = { 'c': 3, 'a': 1, 'b': 2 };
sortKeysAndDo( my_object, show);
This seems to eliminate the issues with prototypes and still provide a sorted iterator for objects. I am not really a JavaScript guru, though, so I'd love to know if this solution has hidden flaws I missed.

Create child objects from parent with same property values [duplicate]

This question already has answers here:
How to put items into grouped arrays where grouped by a particular key
(3 answers)
Closed 9 years ago.
I have a parent object. I want to create child objects from the parent with the same key value pair.
e.g.
parentJSON = {[name:"a1",address:"b1",comp:"c1"],
[name:"a2",address:"b2",comp:"c1"],
[name:"a3",address:"b3",comp:"c2"],
[name:"a4",address:"b4",comp:"c2"],
[name:"a5",address:"b5",comp:"c2"],
[name:"a6",address:"b6",comp:"c3"]}
Now I want to create child objects having same "comp" value.
e.g.
childJSON1 = {[name:"a1",address:"b1",comp:"c1"],
[name:"a2",address:"b2",comp:"c1"]}
childJSON2 = {[name:"a3",address:"b3",comp:"c2"],
[name:"a4",address:"b4",comp:"c2"],
[name:"a5",address:"b5",comp:"c2"]}
childJSON3 = {[name:"a6",address:"b6",comp:"c3"]}
This is what I tried to make it little bit (it will change the parent object with a key indicating number of repetition):
parentJSON = [1,2,3,3,4,4,4,5];
var i=0, x, count, item;
while(i < parentJSON.length) {
count = 1;
item = parentJSON[i];
x = i+1;
while(x < parentJSON.length &&
(x = parentJSON.indexOf(item, x)) != -1) {
count += 1;
parentJSON.splice(x,1);
}
parentJSON[i] = new Array(parentJSON[i],count);
++i;
}
console.log(parentJSON);`
first of all your json is in the incorrect format, it should look like this
[{name:"a1",address:"b1",comp:"c1"},
{name:"a2",address:"b2",comp:"c1"},
{name:"a3",address:"b3",comp:"c2"},
{name:"a4",address:"b4",comp:"c2"},
{name:"a5",address:"b5",comp:"c2"},
{name:"a6",address:"b6",comp:"c3"}]
An array of objects.
My attempt, also very readable.
var result = {};
$.each(parentJSON, function (i, item) {
if(!result[item.comp]) {
result[item.comp] = [];
}
(result[item.comp]).push(item);
});
alert(JSON.stringify(result))
JsFiddle
First of all your json is actually invalid. You may have an array of objects, but not object which contains an array like that. Also your arrays looks more like objects, because the syntax with the dots is used for objects. Here is how I guess should look like:
var parentJSON = [
[{name:"a1",address:"b1",comp:"c1"}],
[{name:"a2",address:"b2",comp:"c1"}],
[{name:"a3",address:"b3",comp:"c2"}],
[{name:"a4",address:"b4",comp:"c2"}],
[{name:"a5",address:"b5",comp:"c2"}],
[{name:"a6",address:"b6",comp:"c3"}]
];
var child1 = parentJSON.slice(0, 2);
var child2 = parentJSON.slice(2, 5);
And you may use the .slice method to get specific elements of the array.
So..you need to clone objects?
maybe tou can try sth like this:
var sergi= {
name: "sergi",
age: 33
};
var bill = (JSON.parse(JSON.stringify(sergi)));
bill.name = "Bill";
console.log(sergi);
console.log(bill);
parentJSON = function(){
return [
{name:"a1",address:"b1",comp:"c1"},
{name:"a2",address:"b2",comp:"c1"},
{name:"a3",address:"b3",comp:"c2"},
{name:"a4",address:"b4",comp:"c2"},
{name:"a5",address:"b5",comp:"c2"},
{name:"a6",address:"b6",comp:"c3"}
];
}
childJSON1 = new parentJSON().slice(0,2);
childJSON2 = new parentJSON().slice(2,5);
childJSON3 = new parentJSON().slice(5,6);
Try this:
DEMO
var data = [
[{name:"a1",address:"b1",comp:"c1"}],
[{name:"a2",address:"b2",comp:"c1"}],
[{name:"a3",address:"b3",comp:"c2"}],
[{name:"a4",address:"b4",comp:"c2"}],
[{name:"a5",address:"b5",comp:"c2"}],
[{name:"a6",address:"b6",comp:"c3"}]
];
var groups = {};
$.each(data, function(i, item) {
var comp = item.comp;
delete item.comp;
if(groups[comp]) {
groups[comp].push(item);
} else {
groups[comp] = [item];
}
});
var result = $.map(data, function(group, key) {
var obj = {};
obj[key] = group;
return obj;
});
alert(JSON.stringify(groups))

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