My data[l][m] contains 1,2,3,4,5
I'm trying to search for a particular number, say '2' in it. Is there a better way to do this?
for (var n = 0; n < data[l][m].length; n++) {
if(data[l][m][n] == num){ // num is equal to '2'
number = data[l][0];
document.form.options[l-1] = new Option(number,number,true,true);
}
}
And how about in: ['id1',['a',[1,2,3,4,5]],['b',[3,4,5,6,7]]]
Many thanks in advance.
If you're already including jQuery, use $.inArray(), like this:
if($.inArray(num, data[l][m]) > -1) {
number = data[l][0];
document.form.options[l-1] = new Option(number,number,true,true);
}
The shorter vanilla JS version is a direct .indexOf() on the Array, but IE doesn't have this by default.
You could use indexOf, although it still has the same O(n) complexity as your for loop:
var pos = data[l][m].indexOf(num);
if (pos !== -1)
{
// element was found
number = data[l][0];
document.form.options[l-1] = new Option(number,number,true,true);
}
Note, however, that older versions of IE do not have the indexOf method for Arrays.
I have no major changes to recommend, but do have a couple tweaks to suggest. The first is to create a temporary reference to data[l] to reduce reading complexity by 1 level. This is a cosmetic change for the benefit of the coder. The other is cache the length of the array you are searching, which helps with performance. If you replace your for loop with the while loop as follows, you can also remove the comparison operations.
var layer1 = data[l];
var n = layer1[m].length;
while (n--) {
if (layer1[m][n] == num) { // num is equal to '2'
number = layer1[0];
document.form.options[l - 1] = new Option(number, number, true, true);
}
}
Related
I would like to know if it is worth to convert an array into a set in order to search using NodeJS.
My use case is that this search is done lot of times, but not necessary on big sets of data (can go up to ~2000 items in the array from time to time).
Looking for a specific id in a list.
Which approach is better :
const isPresent = (myArray, id) => {
return Boolean(myArray.some((arrayElement) => arrayElement.id === id);
}
or
const mySet = new Set(myArray)
const isPresent = (mySet, id) => {
return mySet.has(id);
}
I know that theoretically the second approach is better as it is O(1) and O(n) for the first approach. But can the instantiation of the set offset the gain on small arrays?
#jonrsharpe - particularly for your case, I found that converting an array of 2k to Set itself is taking ~1.15ms. No doubt searching Set is faster than an Array but in your case, this additional conversion can be little costly.
You can run below code in your browser console to check. new Set(arr) is taking almost ~1.2ms
var arr = [], set = new Set(), n = 2000;
for (let i = 0; i < n; i++) {
arr.push(i);
};
console.time('Set');
set = new Set(arr);
console.timeEnd('Set');
Adding element in the Set is always costly.
Below code shows the time required to insert an item in array/set. Which shows Array insertion is faster than Set.
var arr = [], set = new Set(), n = 2000;
console.time('Array');
for (let i = 0; i < n; i++) {
arr.push(i);
};
console.timeEnd('Array');
console.time('Set');
for (let i = 0; i < n; i++) {
set.add(i);
};
console.timeEnd('Set');
I run the following code to analyze the speed of locating an element in the array and set. Found that set is 8-10 time faster than the array.
You can copy-paste this code in your browser to analyze further
var arr = [], set = new Set(), n = 100000;
for (let i = 0; i < n; i++) {
arr.push(i);
set.add(i);
}
var result;
console.time('Array');
result = arr.indexOf(12313) !== -1;
console.timeEnd('Array');
console.time('Set');
result = set.has(12313);
console.timeEnd('Set');
So for your case array.some is better!
I will offer a different upside for using Set: your code is now more semantic, easier to know what it does.
Other than that this post has a nice comparison - Javascript Set vs. Array performance but make your own measurements if you really feel that this is your bottleneck. Don't optimise things that are not your bottleneck!
My own heuristic is a isPresent-like utility for nicer code but if the check is done in a loop I always construct a Set before.
I have search through quite a lot of questions here, but havent found one that i think fits my bill, so if you know of one please link to it.
I have an array that i want to search through for a specific number and if that number is in the array, i then want to take an action and if not then another action.
I have something like this
var Array = ["1","8","17","14","11","20","2","6"];
for(x=0;x<=Array.length;x++)
{
if(Array[x]==8)
then change picture.src to srcpicture1
else
then change picture.src to srcpicture2
}
but this will run the lenght of the array and end up checking the last element of the array and since the last element is not 8 then it will change the picture to picture2.
Now i can see why this happens, i just dont have any ideas as to how to go about checking if an array contains a specific number.
Thanks in advance.
What you can do is write yourself a function to check if an element belongs to an array:
function inArray(array, value) {
for (var i = 0; i < array.length; i++) {
if (array[i] == value) return true;
}
return false;
}
And the just do:
var arr = ["1","8","17","14","11","20","2","6"];
if (inArray(arr, 8)) {
// change picture.src to srcpicture1
} else {
// change picture.src to srcpicture2
}
It's a lot more readable to me.
For extra points you can add the function to the array prototype like so:
Array.prototype.has = function (value) {
for (var i = 0; i < this.length; i++) {
if (this[i] === value) return true;
}
return false;
};
And then the call would be
if (arr.has(8)) // ...
Pushing this even further, you can check for indexOf() method on array and use it - if not - replace it with the code above.
P.S. Try not to use Array for a variable name, since it's reserved for the actual array type.
use this
http://developer.mozilla.org/En/Core_JavaScript_1.5_Reference/Objects/Array/IndexOf
ie version
https://developer.mozilla.org/En/Core_JavaScript_1.5_Reference/Objects/Array/IndexOf#Compatibility
Why don't just you abort the loop when you find the right number :
for(x=0;x<=Array.length;x++)
{
if(Array[x]==8) {
//change picture.src to srcpicture1
break;
}
}
You could sort the array first then check the array only up to the point at which a number would be in the array, were it to exist.
If you have unique keys and a faster retrieval is what you care about a lot, you can consider using a map instead of an array (if there's a hard-bound case of using an array, then it won't work of course). If using a map, you just check "if( num in arr ) ".
Didn't really found a solution to this for Javascript.
What I need; I want to insert an element into an array, but not really overwrite that element. Rather a 'dynamic' insert. Thus Insert element, then shift all elements underneath it by +1 index.
For instance:
I have an array "14S" "16S" "19S".
I know want to insert "15S".
The resulting array: "14S" "15S" "16S" "19S"
What i tried:
fullName = "15S"
low = 5;
cardsS[low] = fullName;
for (var i = low; i < cardsS.length; i++) {
cardsS[i + 1] = cardsS[i];
}
If you know the position you want to insert the element into:
Use the splice method. It's cheap and works exactly like you want. You can also insert multiple elements at once:
var strings = ["14S", "16S", "19S"];
strings.splice(1,0,"15S");
Result
"14S" "15S" "16S" "19S"
You should also use this solution if you don't want the array to be sorted in a specific way.
If you don't know the position you want to insert the element into:
You will have to resort to a push/sort combination, supplying your own sort algorithm (unless the standard sort is enough)
var strings = ["14S", "16S", "19S"];
strings.push("15S");
strings.sort(function(a, b){
if (a is less than b by some ordering criterion)
return -1;
if (a is greater than b by the ordering criterion)
return 1;
// a must be equal to b
return 0;
});
You can use Array.splice to insert a value:
var arr = ["14S","16S","19S"];
arr.splice(1,0,"15S");
// ^position after which to insert
// ^number of elements to delete (none here)
// ^value to insert ("15S" here)
// => arr is now ["14S","15S","16S","19S"]
If you don't know the position, you could use Array.indexOf to determine it:
var arr = ["14S","16S","19S"];
arr.splice((arr.indexOf('14S')>-1 && arr.indexOf(after)+1 || 0),0,"15S");
// ^use indexOf result if applicable or just insert
// (so, if no position, this turns into unshift ;)
You can create a method for it:
function arrayInsertAfter(array, after, value){
after = array.indexOf(after)>-1 && array.indexOf('14S')+1 || 0;
array.splice(after, 0, value);
return array;
}
// usage
var arr = arrayInsertAfter(["14S","16S","19S"],"14S","15S");
// => ["14S","15S","16S","19S"]
MDN link for Array.splice
you just need to use push() and then sort() functions :
var yourArray = ['14S', '16S', '19S'];
yourArray.push('15S');
yourArray.sort();
You want Array.splice.
This splices a new element at position 1.
arr.splice(1, 0, '155');
Fiddle
What you want is the splice function on the native array object.
var arr = [];
arr[0] = "14S";
arr[1] = "16S";
arr[2] = "19S";
arr.splice(2, 0, "15S");
console.log(arr.join());
The resulting array: 14S, 16S, 15S, 19S
If you do that, you will start at cardsS[5], which will have the value of "fullName".
The fact is that your cardsS as 4 values, so your array is 0 to 3. You can see that your array at position 4 is unbind.
Moreover, if you do cardsS[i + 1], you will be at position 6, which is unbind too.
What you have to do is to:
Check how many item you have in your array (Lenght, Count)
Create a new array with Lenght + 1
Check if your new item is > or < to your first item. If it is >, you have to add your first item, if not you have to add your new item
Do this until your array is full.
If you don't want to do like that, you can use Splice function, just check it, or use a sort function from javascript library.
Hope this can help you !
Try This:
fullName ="15S"
cardsS = ["14S", "16S", "19S"];
for (var k in cardsS)
{
if(parseInt(fullName) < parseInt(cardsS[k])){
cardsS.splice(k,0,fullName)
break;
}
}
:)
if you think is better:
fullName ="15S"
cardsS = ["14S", "16S", "19S"];
for (var k = 0; cardsS.length > k; k++)
{
if(parseInt(fullName) < parseInt(cardsS[k])){
cardsS.splice(k,0,fullName)
break;
}
}
In one of your comments you asked the difference between the splice method and the push+sort method.
Splice just cuts up your array and inserts/deletes values based on index.
Using above mentioned example:
var strings = ["14S", "16S", "19S"];
strings.splice(1,0,"15S");
This will literally place the "15S" on index 1. This is why there is a remark "If you don't know the position you want to insert the element into:"
In which case the push+sort method comes into play. At this point you don't have to go about counting your elements and making sure you place everything at the right location.
You literally just push your "15S" at the end of the array, and then have the sort() automatically sort everything for you.
This, granted that your array is indeed sortable. Some setups don't really allow you to sort your arrays (Like colors sorted by color in the rainbow ... you can't just sort them using sort()).
In this case KooiInc's response comes into play. At this point you know where your item needs to be. 15S comes after 14S, so you search for 14S, get that index, and use that index to splice.
At this point you still have to calculate yourself what element 15S will have to go after - in my rainbow example you'll have to actively remember where you want to 'insert' which color based on which colors are in your array at this moment.
In your example the values seem to be suited for normal sorting, so i would go with the Push+sort approach a few people mentioned.
var arr = [1,2,4,5,6];
var element = 3, pos=3;
for(i=arr.length-1; i>=pos-1; i--){
arr[i+1]=arr[i];
}
arr[pos-1]=element;
console.log(arr);
I've already read a few questions here but can't seem to find exactly what I'm looking for. Basically, I need to know if any of the elements present in an array are present in a string. An example:
var currentHref = "http://www.vorcu.com/hello";
var urls = [
"vorcu.com",
"neutronico.com",
"word2.com"
];
So, I need to know if any of the elements in "urls" coincide with any of the text present in "currentHref". Any ideas?
Thanks!
Loop through the array and use search:
str.search(arrItem)
will return the position of the match, or -1 if it isn't found.
Something like this:
for (var i = 0; i < urls.length; i++) {
if (currentHref.indexOf(urls[i]) != -1) {
alert(urls[i]); // found occurence, break or continue
}
}
Or RegExp way (above way is preferred):
var isInArray = RegExp(urls.join('|')).test(currentHref); // true|false
or
var matches = currentHref.match(urls.join('|')); // array of matches ["vorcu.com"]
Everyone is providing the Javascript answer (which I fully support), but just because you mention jQuery I figure I'd provide an alternative:
var curHref = window.location.hostname.split('.'),
// i imagine your static string was just for test purposes
checkHref = curHref[1]+'.'+curHref[2],
urls = [
"vorcu.com",
"neutronico.com",
"word2.com"
];
if($.inArray(checkHref,urls) > -1){
// its in there, do your magic
}
This creates the object I assume you wanted to check (hostname minus www) and if it matches any of the items in urls using the jQuery inArray method.
A function like the following should work:
function containsAny(str, arr) {
for (var i = 0; i < arr.length; i++) {
if (str.indexOf(arr[i]) !== -1) {
return true;
}
}
return false;
}
Alternately you could use the slower but more terse:
RegExp(arr.join('|')).exec(str);
You could use the some method, which is supported by many browsers:
var currentHref = "http://www.vorcu.com/hello";
var urls = [
"vorcu.com",
"neutronico.com",
"word2.com"
];
var containsAny = urls.some(function(x) { return currentHref.indexOf(x) >= 0; });
For compatibility with browsers where some is not supported, the MDN article I've linked provides an implementation you can use.
Make a foreach and then check indexOf ;)
I have an array of items (terms), which will be put as <option> tags in a <select>. If any of these items are in another array (termsAlreadyTaking), they should be removed first. Here is how I have done it:
// If the user has a term like "Fall 2010" already selected, we don't need that in the list of terms to add.
for (var i = 0; i < terms.length; i++)
{
for (var iAlreadyTaking = 0; iAlreadyTaking < termsAlreadyTaking.length; iAlreadyTaking++)
{
if (terms[i]['pk'] == termsAlreadyTaking[iAlreadyTaking]['pk'])
{
terms.splice(i, 1); // remove terms[i] without leaving a hole in the array
continue;
}
}
}
Is there a better way to do this? It feels a bit clumsy.
I'm using jQuery, if it makes a difference.
UPDATE Based on #Matthew Flaschen's answer:
// If the user has a term like "Fall 2010" already selected, we don't need that in the list of terms to add.
var options_for_selector = $.grep(all_possible_choices, function(elem)
{
var already_chosen = false;
$.each(response_chosen_items, function(index, chosen_elem)
{
if (chosen_elem['pk'] == elem['pk'])
{
already_chosen = true;
return;
}
});
return ! already_chosen;
});
The reason it gets a bit more verbose in the middle is that $.inArray() is returning false, because the duplicates I'm looking for don't strictly equal one another in the == sense. However, all their values are the same. Can I make this more concise?
var terms = $.grep(terms, function(el)
{
return $.inArray(el, termsAlreadyTaking) == -1;
});
This still has m * n performance (m and n are the lengths of the arrays), but it shouldn't be a big deal as long as they're relatively small. To get m + n, you could use a hashtable
Note that ECMAScript provides the similar Array.filter and Array.indexOf. However, they're not implemented in all browsers yet, so you would have to use the MDC implementations as a fallback. Since you're using jQuery, grep and inArray (which uses native indexOf when available) are easier.
EDIT:
You could do:
var response_chosen_pk = $.map(response_chosen_items, function(elem)
{
return elem.pk;
});
var options_for_selector = $.grep(all_possible_choices, function(elem)
{
return $.inArray(elem.pk, response_chosen_pk) == -1;
});
http://github.com/danstocker/jorder
Create a jOrder table on termsAlreadyTaking, and index it with pk.
var table = jOrder(termsAlreadyTaking)
.index('pk', ['pk']);
Then you can search a lot faster:
...
if ([] == table.where([{ pk: terms[i].pk }]))
{
...
}
...