Here is my code:
var arr = [[[[[]]]]];
var c = 20;
for (i=0;i<5;i++)
arr[i][0][0][0] = c;
alert(arr[2][0][0][0]);
It doesn't work, but how can I do this?
Most people here are using for loops, which I think are mostly obsolete in the age of anonymous functions in JavaScript. You people should know better :P
Anyway, you can solve this quite nicely in a one-liner. Here are a few scripts that can initialize your array...
If you already have a 4-dimensional array, you can initialize it elegantly like this:
arr.forEach(function(e) { e[0][0][0] = c })
Or, if you're more into map:
arr.map(function(e) { e[0][0][0] = c })
These are assuming you already have c defined, which you do in your code sample (20).
From now on, though, please Google your questions before asking them on stackoverflow. You will receive an answer that has already been accepted :)
It doesn't work because you haven't specified any elements beyond the first one, so the length of array is one and accessing further keys is incorrect.
I think, the most convenient way would be to push a new 3d array with c inside on every iteration (actually I have no idea what you're trying to achieve with this xD):
var arr = [];
var c = 20;
for (i=0;i<5;i++)
arr.push([[[c]]])
alert(arr[2][0][0][0]);
(in your example it's actually 5d, but as you've asked for 4d, writing 4d there)
It is unclear what you want, but I imagine a 4 dimension array is an array that has a set of arrays nested 3 deep, each of which has an array nested 2 deep, each of which has a single array that contains values.
In a one dimension array, you access the value at index 2 by:
arr[2];
In a two dimension array, you'd access the value at (2,3) by:
arr[2][3]
and so on until you get to the value at (2,3,1,2) in a four dimension array by:
arr[2][3][1][2]
and if that was the only value in the array, it would look like:
[,,[,,,[,[,,'value at 2312']]]];
If there was also a value at (1,1,0,2) the array would now look like:
[,[,[[,,'value at 1102']]],[,,,[,[,,'value at 2312']]]];
There can only be values in the last nested array, the value at indexes in every other array must be another array (for the lower dimensions), so to insert at value at, say (2,1,3,1) and assign it a value of 6, you need to loop over the array and inspect each index. If it's not already an array, insert an array and keep going, e.g.:
// Insert value in arrary at coord
// coord is a comma separated list of coordinates.
function insertValue( array, coord, value) {
var coords = coord.split(',');
var arr = array;
for (var c, i=0, iLen=coords.length-1; i < iLen; i++) {
c = coords[i];
if (!Array.isArray(arr[c])) arr[c] = [];
arr = arr[c];
}
arr[coords[i]] = value;
return array;
}
document.write('result: ' + JSON.stringify(insertValue([],'1,2,1,3','at 1213')));
I don't understand what you are trying to do in the OP: are you trying to create a value of 20 at coordinates (0,0,0,0), (1,0,0,0), (2,0,0,0), etc.? If that is the case, you also need a fill function that will iterate for the required number of times and pass suitable arguments to insertValue.
If that's what you want, then given the above you should be able to write such a function. On the first iteration it would pass:
insertValue(array, '0,0,0,0', 20)
and on the second:
insertValue(array, '1,0,0,0', 20)
and so on. You may wish to modify the function so that instead of the coords being a CSV string, you pass an array like [0,0,0,0] (which is what split turns the CSV string into), but that's up to you.
Note that you must pass all 4 dimensions, otherwise you will replace one of the dimension arrays with a value and effectively delete all other points in that dimension sector.
PS
ES5 introduced forEach, which helps encapsulate loops but doesn't necessarily mean less code, or faster execution, than an equivalent for loop:
// Insert value in arr at coord
// coord is a comma separated list of coordinates.
function insertValue( array, coord, value) {
var arr = array;
var coords = coord.split(',');
var last = coords.pop();
coords.forEach(function(c) {
if (!Array.isArray(arr[c])) arr[c] = [];
arr = arr[c];
})
arr[last] = value;
return array;
}
Create array with 5 nested arrays:
var arr = [[[[[]]]], [[[[]]]], [[[[]]]], [[[[]]]], [[[[]]]], [[[[]]]]];
var c = 20;
for (i=0;i<5;i++)
arr[i][0][0][0] = c;
alert(arr[2][0][0][0]);
EDIT: if you dig into functional programming and recursion, you can initialize your multidimensional array with just a few lines of code. Let's say you want 4-dimensional array with length 10 of each dimension:
function createNDimensionalArray(n, length) {
return n === 1
? new Array(length)
: Array.apply(null, Array(length)).map(createNDimensionalArray.bind(null, n - 1, length));
}
var arr = createNDimensionalArray(4, 10);
console.log(arr); // creates 4-dimensional array 10x10x10x10
Notice that initialization like this could be very slow if you create very big arrays (e.g. createNDimensionalArray(5, 10000).
If you prefer to set length of each dimension, you can modify previous the solution like this:
function createNDimensionalArray(dims) {
return dims.length === 1
? new Array(dims[0])
: Array.apply(null, Array(dims[0])).map(createNDimensionalArray.bind(null, dims.slice(1)));
}
var arr = createNDimensionalArray([2, 3, 4, 5]);
console.log(arr); // creates 4-dimensional array 2x3x4x5
Related
Let's assume I have two arrays with same length:
var a=[5,2,8,12,15,72,3,9];
var b=[,3,,5,19,,71,];
in Javascript, how can I merge these two arrays so that in every index the new array contains the corresponding b element, if is is not empty, the corresponding element of a.
The new array c should be:
c = [5,3,8,5,19,72,71,9]
Note: the order of the elements must not be changed.
So assuming that A will always have an element while it is not always true that B will have one. Then the below code should word.
Essentially just loop through B check if there is an input, if there is push it to the new array if not grab the value in A
This runs in linear time.
var a=[5,2,8,12,15,72,3,9];
var b=[,3,,5,19,,71,];
function createNewArray(a, b){
let newArray = [];
for(let i=0;i<=b.length;i++){
if(b[i]){
newArray.push(b[i])
} else {
newArray.push(a[i])
}
}
return newArray
}
console.log(createNewArray(a,b))
I'm having a tough time figuring out how to loop through an array and if certain items do exist within the array, i'd like to perform a .slice(0, 16) to kind of filter an already existing array (lets call that existing array "routes").
For example, a previous process will yield the following array:
points = ['=00ECY20WA200_RECV_P1SEL',
'=00ECY20WA200_RECV_P2SEL',
'=00RECV_C1A_EINCSCMPP1',
'=00RECV_C1A_EINCSCMPP2',
'=00BYPS_C1A_EINCSCMP',
'=00ECY20WA200_BYPS_SPSL1',
'=00ECC92AG184YB01',
'=00ECC92AG185YB01',
'=00ECC92AG186YB01',
'=00ECC92AG187YB01',
]
So if any of the above items exist in the "points" Array, which in this case they all do (but in some cases it could just be 1 of the 10 items existing there), I'm trying to perform routes.slice(0, 16) to the other already existing array.
I've tried lots of different ways (for loops with if statements) and at this point I'm not sure if its my syntax or what, but I'm back at square 0 and I don't even have a competent piece of code to show for. Any direction would be greatly appreciated.
You could use a hash table for checking and filtering.
var points = ['=00ECY20WA200_RECV_P1SEL', '=00ECY20WA200_RECV_P2SEL', '=00RECV_C1A_EINCSCMPP1', '=00RECV_C1A_EINCSCMPP2', '=00BYPS_C1A_EINCSCMP', '=00ECY20WA200_BYPS_SPSL1', '=00ECC92AG184YB01', '=00ECC92AG185YB01', '=00ECC92AG186YB01', '=00ECC92AG187YB01'],
hash = Object.create(null),
filtered = points.filter(function (a) {
if (!hash[a.slice(0, 16)]) {
hash[a.slice(0, 16)] = true;
return true;
}
});
console.log(filtered);
ES6 with Set
var points = ['=00ECY20WA200_RECV_P1SEL', '=00ECY20WA200_RECV_P2SEL', '=00RECV_C1A_EINCSCMPP1', '=00RECV_C1A_EINCSCMPP2', '=00BYPS_C1A_EINCSCMP', '=00ECY20WA200_BYPS_SPSL1', '=00ECC92AG184YB01', '=00ECC92AG185YB01', '=00ECC92AG186YB01', '=00ECC92AG187YB01'],
pSet = new Set,
filtered = points.filter(a => !pSet.has(a.slice(0, 16)) && pSet.add(a.slice(0, 16)));
console.log(filtered);
EDIT: So it seems like you want to remove an element from an array called routes for each element in the points array. This is how you could do this:
function removeBrokenRoutes(brokenPoints, routes){
for(let pt of brokenPoints){
let index = routes.indexOf(pt);
if(index !== -1) routes.splice(index,1);
}
return routes;
}
Keep in mind that the larger the arrays, the more time this is going to take to complete.
You could use the filter and indexOf methods in combination:
var arr = [/* all the data you're checking against */];
var points = [/* the data you're checking for */];
var filteredArr = arr.filter(function(x) {
// will return -1 if the point is not found
return points.indexOf(x) !== -1;
});
filteredArr will contain all the points that appear in both arrays. The filter function works by taking a function with one argument x, which represents each item in the array. if the function returns true, the item will be added to the new array (filteredArr), and if false the function will move on to the next item. indexOf will check if the item is found in the other array. Also it is important to note that you will need a more complex solution (such as a hashtable) if the data set is very, very large as this is not necessarily the most performant method. But it's a good place to start as it is easy to understand.
Very quick question,
I want to order an array by specific value and put it always at the middle.
For example... if my array is:
myarr = [1,2,3,4,5];
the function middlelizeArr(myarr,2) should me returns this array:
result [5,1,2,3,4]
and find the best condition in case of even array
myarr = [1,2,3,4,5,6,7,8];
result [7,8,1,2,3,4,5,6];
How could I do this? Someone can help me?
At first you need to have a size of an array and find the location of a number you want to put into the middle
If,
n = size of an array
l = location of the number you want to put it into the middle
if n/2 > l, then shift your number clockwise otherwise shift it anti clockwise.
This is done by comparing the index of the "middle" number to the length of the array, and then shifting (and pushing) until they're equal.
I've implemented it the following way:
function middlelizeArray(array, middle) {
var goal = Math.trunc(array.length/2);
while(array.indexOf(middle) != goal) {
array.push(array.shift());
}
return array;
}
This could also be added directly to the array prototype. This would allow you to just say myArray.middlelize(2);
That would be done like so:
Array.prototype.middlelize = function(middle) {
var goal = Math.trunc(this.length/2);
while(this.indexOf(middle) != goal) {
this.push(this.shift());
}
return this;
}
I want to use an array to look up a value given a key. AFAIK, it should be possible when converting the float to a string, like the second example below: (jsfiddle)
arr = [];
arr[1.3] = "One point three";
console.log(arr.length);
arr = [];
arr["1.3"] = "One point three";
console.log(arr.length);
But both result in a zero-length array. What am I doing wrong? I.e. how can I look up an object/string/whatever given a float value?
It would be awesome to have a reference guide on common operations when using having to look up values, such as:
get an element, given a float key
get total number of elements
test if float key exists
put new float key / value pair
and maybe others, such as loop through all keys/values
Array's index must be an integer for adding it as an array item. If you will pass to the [] not an integer, it will be added as a property.
arr = [];
arr[1.3] = "One point three";
console.log(arr.length);
console.log(arr.hasOwnProperty('1.3'));
console.log(Object.keys(arr).length);
I could be wrong, but it seems you are trying to create a dict. I would just use an object like others have suggested.
var arr = {
1.2: 'One Point Three'
}
arr[1.2] or arr["1.2"] // One Point Three
or you can use es6 Map
var arr = new Map()
arr.set(1.3, "One Point Three")
arr.get(1.3) // One Point Three
arr.size // 1
An array takes an integer value as index.
You should be using an Object for this kind of mapping.
var arr = {};
arr[1.3] = "One point three";
console.log(Object.keys(arr).length);
Suren's answer was the first, and gave me what I needed to establish a reference of operations:
Insert an item:
var x = 1.3;
// Not actually an array! arr.length will be undefined. Although
// an array could still be used, it seems
var arr = {};
arr[x] = "One point three";
Count items:
Object.keys(arr).length
Test if key exists:
arr.hasOwnProperty(x)
Get an element:
arr[x]
Loop through key/value pairs
for (key in arr)
{
var value = arr[key];
}
Interesting quirks
+1 to James Emanon for several points: Firstly, showing that a string is not necessary for lookup:
arr[1.3] // works
Secondly, the array can be defined as an object like so:
arr = {
1.3: "One point three"
};
Thirdly, ES6 provides a Map object. Will be useful.
I am trying to set up an array in jQuery and I then need to do a for loop on it. But it seems that I cant use an associative array for some reason?
var items = new Array();
items['foo'] = 123456;
items['bar'] = 789012;
items['baz'] = 345678;
items['bat'] = 901234;
alert(items.length);
This is just a test, but it return 0?
You can't make associative array in JavaScript like what you want, instead you can use Object.
For example:
var items = {
foo : 123456,
bar : 789012,
baz : 345678,
bat : 901234
}
And to calculate the length you can do:
var getObjectSize = function(obj) {
var len = 0, key;
for (key in obj) {
if (obj.hasOwnProperty(key)) len++;
}
return len;
};
Use: getObjectSize(items); // output: 4
For more see here.
Another one is:
Object.keys(items).length;
But not supported by all browsers.
var items = new Array();
items['foo'] = 123456;
The problem lies in the very first line. You believe that you are adding an item to the array at the index foo, but you are actually adding a property to the items variable with a key foo and value 123456. If you were to type items.foo it would give you back your 123456.
The problem with this approach is that adding a property to an array does not magically increase it's length.
If you want to have non-numeric indexes, you need to use an object instead of an array:
var items = {
foo: 123456,
bar: 789012,
baz: 345678,
bat: 901234
};
Another approach might be to set up two different arrays, which you construct in parallel:
var items = [], items2 = [];
items.push('foo');
items2.push(123456);
// etc.
alert(items2.length);
The efficiency of this approach depends on how you'll use it. If you're only going to loop through the list of items and do something to each of them, this approach may be more efficient. But if you need to use it like an associative array (items['foo']), then you're better off building an object.
The .length property returns the highest numerical index of the array. Thus, in your case, there is no numerical index and it returns 0. Try
items[98] = "something";
items.length will be 98..! Use the .length property with caution, and if you also want to count the non-numerical indici, loop over the Object (an Array is also an Object) and count its ownProperties.