I need help with a loop... it's probably simple but I'm having difficulty coding it up.
Basically, I need to check existing Ids for their number so I can create a unique id with a different number. They're named like this: id="poly'+i'" in sequence with my function where i is equal to the number of existing elements. Example: Array 1, Array 2, Array 3 corresponding with i=1 for the creation of Array 1, i=2 for Array 2, etc.
Right now i is based on the total number of existing elements, and my "CreateNew" function is driven off x=i+1 (so the example above, the new element will be named Array 4). The problem is that if you delete one of the middle numbers, the "Create" function will duplicate the high number. i.e. Array 1, 2, 3 delete 2, create new-> Array 1, 3, 3.
I need an if() statement to check if the array already exists then a for() loop to cycle through all i's until it validates. Not sure how to code this up.
The code I'm trying to correct is below (note I did not write this originally, I'm simply trying to correct it with my minimal JS skills):
function NewPanel() {
var i = numberOfPanels.toString();
var x = (parseInt(i)+1).toString();
$('#items').append('<div onclick="polygonNameSelected(event)" class="polygonName" id="poly'+i+'"> Array '+ x +' </div>');
$('div[id*=poly]').removeClass('selected');
$('#poly'+i).addClass('selected');
$('#poly'+i).click(function() {
selectedPolygon = i;
$('div[id*=poly]').removeClass('selected');
$(this).addClass('selected');
});
}
THANK YOU! :)
Please clarify "The problem is that if you delete one of the middle numbers, ". What do you mean by delete? Anyway, the simplest solution is to create two arrays. Both arrays will have the same created id's. Whenever an id is created in the first array, an id will be added to the second array. So when it is deleted from first array, check your second array's highest value and then create this id in first array. I hope this did not confuse you.
Well it is hard to tell why you cannot just splice the array down. It seems to me there is a lot of extra logic involved in the tracking of element numbers. In other words, aside from the index being the same, the ids become the same as well as other attributes due to the overlapping 1, 3, 3 (from the example). If this is not the case then my assumption is incorrect.
Based on that assumption, when I encounter a situation where I want to ensure that the index created will always be an appending one, I usually take the same approach as I would with a database primary key. I set up a field:
var primaryKeyAutoInc = 0;
And every time I "create" or add an element to the data store (in this case an array) I copy the current value of the key as it's index and then increment the primaryKeyAutoInc value. This allows for the guaranteed unique indexing which I am assuming you are going for. Moreover, not only will deletes not affect future data creation, the saved key index can be used as an accessor.
Related
Suppose I have an Javascript array,
var example = [and, there,sharma<br, />, ok, grt]
Now I want to randomly delete some array values - but not those values which have
<br
in them, in the above example, I want to make sure
"sharma<br" is not deleted.
I also do not want to delete "/>".
Can anyone help me. I would really appreciate the answer.
First of all, that is not a valid array, unless you are missing the string quotes. Anyway, what you are searching for is Array.Filter. In your case :
var filtered = example.filter(v => v.indexOf("<br") != -1 || v.indexOf("/>") != -1)
If I have understood the problem correctly, then you want to keep those entries in the array which have substrings "<br" and "/>"
If thats the case, you can try using javascript string method includes() to see if a string contains a particular substring.
JavaScript array must be created as below
var example = ["and"," there"",sharma<br","/>","ok"," grt"];
Using splice method , to delete the array values specifying the index positions.
array splice() method changes the content of an array, adding new elements while removing old elements.
Syntax
Its syntax is as follows −
array.splice(index, howMany, [element1][, ..., elementN]);
Parameter Details
index −
Index at which to start changing the array.
howMany −
An integer indicating the number of old array elements to remove. If howMany is 0, no elements are removed.
element1, ..., elementN −
The elements to add to the array. If you don't specify any elements, splice simply removes the elements from the array.
Return Value
Returns the extracted array based on the passed parameters.
var removed = arr.splice(2, 2);
This would remove your suggested output to be my assumption .
I am learning Javascript and I come from a Python background.
So, it's fairly intuitive to me to try and index an array from the end i.e using negative indices.
From what I have read so far, Javascript doesn't support them.
However, I found something which seems interesting but I am unable to understand the reason behind this.
todos = ['item1', 'item2', 'item3']
function updateTodos(index, new_value) {
todos[index] = new_value
console.log(todos)
}
function deleteTodos(index) {
todos.splice(index)
console.log(todos)
}
deleteTodos(-1)
updateTodos(-1, 'new_item')
deleteTodos(-1)
Output
["item1", "item2"]
["item1", "item2", -1: "new_item"]
["item1", -1: "new_item"]
Q: Why is deleteTodos able to delete the correct by index while updateTodos isn't?
Q: How can I accommodate for this behavior of negative indexing in updateTodos and any function dealing with the array data structure in general?
As far as I can make out, the indexing in updateTodos looks for the index variable and update the value at that index, if it exists, else, it creates a key-value pair. The splice method supports negative indexing, doesn't it?
I would appreciate if you can clarify my reasoning and/or help me with useful resources to understand this concept better.
According to MDN, splice does support negative indexing.
https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Array/splice
Index at which to start changing the array (with origin 0). If greater
than the length of the array, actual starting index will be set to the
length of the array. If negative, will begin that many elements from
the end of the array (with origin 1).
So, that's why deleting works.
To enable negative indexing in update, you could check if the supplied argument is negative. If it is, it is a simple manner of using array.length + index to have the python-like indexing.
2 things to add to the accepted answer:
1) Remember that when using splice that if you don't specify an amount of items to delete (second argument) then everything from the index you specify to the end of the array will be deleted. From your question I doubt this is what you want.
2) Splice can also be used to add elements to an array (third argument, fourth argument etc.) so would work fine for your update function.
A complete example to fix both issues would be like this:
function updateTodos(index, new_value) {
todos.splice(index, 1, new_value);
}
function deleteTodos(index) {
todos.splice(index, 1);
}
You could get even fancier and combine them both into one function where if you specify a value then that gets updated else it gets deleted, but it's probably unnecessary.
Prepending that a solution only needs to work in the latest versions of Chrome, Firefox, and Safari as a bonus.
-
I am trying to use an associative array for a large data set with knockout. My first try made it a true associative array:
[1: {Object}, 3: {Object},...,n:{Object}]
but knockout was not happy with looping over that. So I tried a cheating way, hoping that:
[undefined, {Object}, undefined, {Object},...,{Object}]
where the location in the array is the PK ID from the database table. This array is about 3.2k items large, and would be iterated over around every 10 seconds, hence the need for speed. I tried doing this with a splice, e.g.
$.each(data, function (index, item) {
self.myArray.splice(item.PKID, 0, new Object(item));
}
but splice does not create indices, so since my first PKID is 1, it is still inserted at myArray[0] regardless. If my first PK was 500, it would start at 0 still.
My second thought is to initialize the array with var myArray = new Array(maxSize) but that seems heavy handed. I would love to be able to use some sort of map function to do this, but I'm not really sure how to make the key value translate into an index value in javascript.
My third thought was to keep two arrays, one for easy look up and the other to store the actual values. So it combines the first two solutions, almost, by finding the index of the object in the first example and doing a lookup with that in the second example. This seems to be how many people manage associative arrays in knockout, but with the array size and the fact that it's a live updating app with a growing data set seems memory intensive and not easily manageable when new information is added.
Also, maybe I'm hitting the mark wrong here? We're putting these into the DOM via knockout and managing with a library called isotope, and as I mentioned it updates about every 10 seconds. That's why I need the fast look up but knockout doesn't want to play with my hash table attempts.
--
clarity edits:
so on initial load the whole array is loaded up (which is where the new Array(maxLength) would go, then every 10 seconds anything that has changed is loaded back. That is the information I'm trying to quickly update.
--
knockout code:
<!-- ko foreach: {data: myArray(), afterRender: setInitialTileColor } -->
<div class="tile" data-bind="attr: {id: 'tileID' + $data.PKID()}">
<div class="content">
</div>
</div>
<!-- /ko -->
Then on updates the hope is:
$.each(data.Updated, function (index, item) {
var obj = myModel.myArray()[item.PKID];
//do updates here - need to check what kind of change, how long it's been since a change, etc
}
Here is a solution how to populate array items with correct indexes, so it doesn't start from the first one (0 (zero) I meant)
just use in loop
arr[obj.PKID] = obj;
and if your framework is smart (to use forEach but not for) it will start from your index (like 500 in case below)
http://jsfiddle.net/0axo9Lgp/
var data = [], new_data = [];
// Generate sample array of objects with index field
for (var i = 500; i < 3700; i++) {
data.push({
PKID: i,
value: '1'
});
}
data.forEach(function(item) {
new_data[item.PKID] = item;
});
console.log(new_data);
console.log(new_data.length); // 3700 but real length is 3200 other items are undefined
It's not an easy problem to solve. I'm assuming you've tried (or can't try) the obvious stuff like reducing the number of items per page and possibly using a different framework like React or Mithril.
There are a couple of basic optimizations I can suggest.
Don't use the framework's each. It's either slower than or same as the native Array method forEach, either way it's slower than a basic for loop.
Don't loop over the array over and over again looking for every item whose data has been updated. When you send your response of data updates, send along an array of the PKIds of the updated item. Then, do a single loop:
.
var indexes = []
var updated = JSON.parse(response).updated; // example array of updated pkids.
for(var i=0;i<allElements.length;i++){
if(updated.indexOf(allElements[i].pkid)>-1)
indexes.push(i);
}
So, basically the above assumes you have a simple array of objects, where each object has a property called pkid that stores its ID. When you get a response, you loop over this array once, storing the indexes of all items that match a pk-id in the array of updated pk-ids.
Then you only have to loop over the indexes array and use its elements as indexes on the allElements array to apply the direct updates.
If your indexes are integers in a reasonable range, you can just use an array. It does not have to be completely populated, you can use the if binding to filter out unused entries.
Applying updates is just a matter of indexing the array.
http://jsfiddle.net/0axo9Lgp/2/
You may want to consider using the publish-subscribe pattern. Have each item subscribe to its unique ID. When an item needs updating it will get the event and update itself. This library may be helpful for this. It doesn't depend upon browser events, just arrays so it should be fairly fast.
I have some script that is calling AJAX information from a server and then displaying the information into blocks on the page. And every 8 seconds those blocks will fade to a new set of information.
The information from the server is stored in a fixed queue that pushes new items to it every 8 seconds.
And for each block I have it grab a random item from that array to show. The only thing is my blocks are getting a lot of duplicates.
Is there a way to check and see if that array item has been called from another block, and if so it will move on to find another item not in use.
var queue = FixedQueue( 50 );
$(document).ready(function() {
$('.submit').click(function(){
setInterval(function(){
queue.push(fulltweet);
},8000);
});
});
setInterval(function(){
randotime = intervals[Math.floor(Math.random()*intervals.length)];
$('.block1', '.photo1:nth-child(1)').queue(function(){
$(this).hide();
$(this).html(queue[0]);
$(this).fadeIn(2000);
$(this).delay(randotime);
$(this).dequeue();
});
$('.block1', '.photo1:nth-child(1)').fadeOut(2000);
},randotime);
I was creating a random number based on the length of the queue and using that to call queue[rando] but again, I keep getting duplicates in the blocks.
First, if you don't want duplicate items in your array, don't let them to be duplicate. Before inserting new items to your array, control whether it exists in your array or not. Using equality operation may not work if you use objects instead of primitive types(string, integer, etc..). Therefore you need a function checks if a given element exists in the array before insertion, and this function must use a equals function which compares two given objects.
Secondly, javascript allows you to add fields to objects in runtime. So when a block reaches and displays an object, you can put a field over this object. Let's say its name is 'inuse'.
When block A reaches the object:
object.inuse = true;
When block B reaches the same object randomly:
var object = pickRandomly();
while (object.inuse) {
object = pickRandomly();
}
// here's the unique object which is not used by another block.
I hope that helps.
If you can provide a sample code, I can provide a better answer.
I've been given two arrays, each of which has several objects within them. I'm trying to make it so that when a certain dropdown selection is made, it pushes that "flight information" into a "flight summary" div, but I'm having a hard time figuring out how to do it.
var possibleDepartureFlights=[{year:2012,month:11,day:13,hour:17,minute:37,price:137.38} and so on];
var possibleReturnFlights=[{year:2012,month:11,day:18,hour:21,minute:45,price:189.46} and so on];
Each var has 10 objects within the array, each of which has all those properties.
And as a bonus question, I've figured out how to hide a "submit" button when the return flight selected is earlier than the departure, but I can't figure out how to make the submit button come back when a different selection is made!
function displayDivs() {
var departureValue = $('#departureFlightsControl').val();
var returnValue = $('#returnFlightsControl').val();
if (departureValue != "default") {
$('.CumulativeSummary').addClass('totalAvailable');
$('.DepartureSummary').addClass('flightChosen');
}
if (returnValue != "default") {
$('.CumulativeSummary').addClass('totalAvailable');
$('.ReturnSummary').addClass('flightChosen');
}
if ($('#returnFlightsControl').val() < $('#departureFlightsControl').val()) {
$('.SubmitArea').hide();
}
Sorry if this question is vague! I'm new to jQuery and JavaScript, so I'm not really sure what I'm doing (and I'm not even really sure what to Google for to find the answer to my problem(s)). Please use small words, as if you're speaking to a child. Thanks!
Your question is really too broad, anyways... Suppose you have following
var possibleDepartureFlights=[
{year:2012,month:10,day:13,hour:10,minute:37,price:137.38},
{year:2012,month:11,day:15,hour:17,minute:47,price:150.50}
];
The possibleDepartureFlights is an array of two objects and the first element of the array is the first object and it's {year:2012,month:10,day:13,hour:10,minute:37,price:137.38} and it's index is 0 and the second element in your possibleDepartureFlights array is the second object and it's {year:2012,month:11,day:15,hour:17,minute:47,price:150.50} and it's index is 1. Now, if you want to access the month property of the first item of the array then you can write like
alert(possibleDepartureFlights[0].month); // this will alert 10
For the month of the second item/object in the array you can write
alert(possibleDepartureFlights[1].month); // this will alert 11
To loop through the array and print out the each property of every objects, you can try this
for(i=0;i<possibleDepartureFlights.length;i++)
{
console.log(possibleDepartureFlights[i].year);
console.log(possibleDepartureFlights[i].month);
console.log(possibleDepartureFlights[i].hour);
console.log(possibleDepartureFlights[i].minute);
console.log(possibleDepartureFlights[i].price);
}
An Example Here.
Remember, this is only a short example and there are more about arrays and objects in JavaScript. Also remember that you can loop an object with for in like for loop. Also this one could be helpful too.