Is element in array js - javascript

Following an old question, I still have a problem:
a = ["apple", "banana", "orange", "apple"];
a.indexOf("apple") = 0
What is the easiest way to find BOTH indexes of "apple" element in array? I want to delete them both at once - is it possible?

That's the task for filter method:
var noApples = a.filter(function(el) { return el != "apple"; })

What is the easiest way to find BOTH indexes of "apple" element in array?
You asked that, but also asked about deleting. I'll tackle indexes first, then deletion.
Indexes:
There's no shortcut, you have to loop through it. You can use a simple for loop:
var indexes = [];
var index;
for (index = 0; index < a.length; ++index) {
if (a[n] === "apple") {
indexes.push(index);
}
});
Or two ES5 options: forEach:
var indexes = [];
a.forEach(function(entry, index) {
if (entry === "apple") {
indexes.push(index);
}
});
Or reduce:
var indexes = a.reduce(function(acc, entry, index) {
if (entry === "apple") {
acc.push(index);
}
return acc;
}, []);
...although frankly that does't really buy you anything over forEach.
Deletion:
From the end of your question:
I want to delete them both at once - is it possible?
Sort of. In ES5, there's a filter function you can use, but it creates a new array.
var newa = a.filter(function(entry) {
return entry !== "apple";
});
That basically does this (in general terms):
var newa = [];
var index;
for (index = 0; index < a.length; ++index) {
if (a[n] !== "apple") {
newa.push(index);
}
});

Array.indexOf takes a second, optional argument: the index to start from. You can use this inside a loop to specify to start from the last one.
var indices = [],
index = 0;
while (true) {
index = a.indexOf("apple", index);
if (index < 0) {
break;
}
indices.push(index);
}
Once indexOf returns -1, which signals "no element found", the loop will break.
The indices array will then hold the correct indices.
There is an example on the Mozilla page on indexOf which has some equivalent code. I'm not so much of a fan because of the increased duplication, but it is shorter, which is nice.

A for loop will do the trick. Or use forEach as T.J. Crowder suggests in his elegant answer.
I combined both an example of how to get appleIndexes and also how to "delete" them from the original array by virtue of creating a new array with all but apples in it. This is using oldSchool JavaScript :)
a = ["apple", "banana", "orange", "apple"];
appleIndexes = [];
arrayOfNotApples = [];
for (var i = 0; i < a.length; i++)
{
if (a[i] == "apple")
{
appleIndexes.push(i);
} else {
arrayOfNotApples.push(a[i]);
}
}

If you need to remove elements from an array instance without generating a new array, Array.prototype.splice is a good choice:
var a,
i;
a = ["apple", "banana", "orange", "apple"];
for (i = a.indexOf('apple'); i > -1; i = a.indexOf('apple')) {
a.splice(i, 1);
}
If you can use a new array instance, then Array.prototype.filter is a better choice:
var a,
b;
a = ["apple", "banana", "orange", "apple"];
b = a.filter(function (item, index, array) {
return item !== 'apple';
});

Use the start parameter in array.indexOf(element, start), as described in http://www.w3schools.com/jsref/jsref_indexof_array.asp.
Example:
var a = [1, 3, 4, 1];
var searchElement = 1;
var foundIndices = [];
var startIndex = 0;
while ((index = a.indexOf(searchElement, startIndex)) != -1) {
foundIndices.push(index);
startIndex = index + 1;
}
console.log(foundIndices); // Outputs [0, 3];

A good old while loop :
var i = a.length;
while (i--) {
if (a[i] === 'apple') {
a.splice(i, 1);
}
}
Inside a function :
function removeAll(value, array) {
var i = array.length;
while (i--) {
if (array[i] === value) {
array.splice(i, 1);
}
}
return array;
}
Usage :
removeAll('apple', a);

A couple of recursive solutions.
Javascript
function indexesOf(array, searchElement, fromIndex) {
var result = [],
index = array.indexOf(searchElement, fromIndex >>> 0);
if (index === -1) {
return result;
}
return result.concat(index, indexesOf(array, searchElement, index + 1));
}
function removeFrom(array, searchElement, fromIndex) {
var index = array.indexOf(searchElement, fromIndex >>> 0);
if (index !== -1) {
array.splice(index, 1);
removeFrom(array, searchElement, index);
}
return array;
}
var a = [0, 1, 0, 2, 0, 3, 0, 4, 0, 5, 0, 6, 0, 7, 0, 8, 0, 9, 0, 10, 0];
console.log(indexesOf(a, 0));
console.log(removeFrom(a, 0));
Output
[0, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20]
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
On jsFiddle

The fastest, most compatible, route would be to walk the array backwards in a for loop.
for (var a = array.length;a--;)
if (array[a] == 'apple') array.splice(a,1);

if you want to remove all occurrences, you could also use Array.splice recursively
function remove(list, item) {
if(list.indexOf(item)<0)
return list;
list.splice(list.indexOf(item),1);
return list;
}

Related

Given an array of integers return positives, whose equivalent negatives present in it

I have implemented solution in javascript using two loops, below is the code
function getNums(arr){
var res = [];
var found = {};
var i, j;
var arrLen = arr.length;
for(i=0; i<arrLen; i++){
if(!found.hasOwnProperty(arr[i])){
for(j=0; j<arrLen; j++){
if(arr[i]+arr[j] === 0){
var num = arr[i];
if(num > 0){
res.push(num);
found[num] = 1;
}
}
}
}
}
return res;
}
console.log(getNums[-1, -2, 0, -4, 1, 4, 6]); // Output: [1, 4]
Whose time complexity is O(n2). Can someone suggest better solution / refined above to have less complexity?
You can just add the array to a Set and filter for inclusion in the set. Determining if something is in a set is constant time:
let arr = [-1, 2, 3, 1 , 3, -3, 4, -6]
let s = new Set(arr)
// all positive numbers with corresponding negatives in the set
let filtered = arr.filter(item => item > 0 && s.has(-1 * item))
console.log(filtered)
An alternative is to sort the array and then walk two pointers up the array as making matches along the way. The result will be sorted, however, which may not be the same order as the original array:
let arr = [-2, -3, 2, 5, 3, 1, -6, 2, -5]
arr.sort()
// get startig indexes
let i = 0, j = arr.findIndex(n => n > 0)
let res = []
if (j > -1) { // only if there are positive numbers in the array
while(arr[i] < 0 && j < arr.length){
if (-1 * arr[i] === arr[j]){
res.push(arr[j++])
} else if(-1 * arr[i] > arr[j]){
j++
} else if(-1 * arr[i] < arr[j]){
i++
}
}
}
console.log(res)
You could take a single loop approach by counting the values.
function getNums(array) {
var count = Object.create(null),
result = [];
array.forEach(v => {
if (count[-v]) {
result.push(Math.abs(v));
count[-v]--;
return;
}
count[v] = (count[v] || 0) + 1;
});
return result;
}
console.log(getNums([1, 2, -3, -4, 2, 3, 4, 4, -4]));
Before the downvotes... This answer is not the shortest javascript code, but the algorithm - I think it is what the original question was about.
One way to get rid of nested loops is to use more memory to store intermediate structures. In your case, you want to store not just the "found" flag, but negative, positive values as well, so that at every iteration you can set the found flag. Then you also use the "found" flag to prevent adding the results 2nd time.
var f = function(arr) {
let hash = {};
let res = [];
for (var i = 0; i < arr.length; i++) {
// put value into the hash map for future use
hash[arr[i]] = arr[i];
var absVal = Math.abs(arr[i]);
// if value is not 0 AND if it has not been found yet (x+value hash) AND if both negative and positive values are present
if( arr[i] !== 0 && !hash["x"+absVal] && (hash[arr[i]] + hash[-arr[i]] === 0)){
// then set the found hash to true
hash["x"+absVal] = true;
// and push to the resut
res.push(absVal);
}
}
// return the result
return res;
}
Another solution is to use filter and includes prototype functions which are well optimized.
const getNums = (arr) => arr.filter((num, index) => num > 0 && !arr.includes(num, index + 1) && arr.includes(-num));

Find Missing Numbers from Unsorted Array

I found this JavaScript algorithm excercise:
Question:
From a unsorted array of numbers 1 to 100 excluding one number, how will you find that number?
The solution the author gives is:
function missingNumber(arr) {
var n = arr.length + 1,
sum = 0,
expectedSum = n * (n + 1) / 2;
for (var i = 0, len = arr.length; i < len; i++) {
sum += arr[i];
}
return expectedSum - sum;
}
I wanted to try and make it so you can find multiple missing numbers.
My solution:
var someArr = [2, 5, 3, 1, 4, 7, 10, 15]
function findMissingNumbers(arr) {
var missingNumbersCount;
var missingNumbers = [];
arr.sort(function(a, b) {
return a - b;
})
for(var i = 0; i < arr.length; i++) {
if(arr[i+1] - arr[i] != 1 && arr[i+1] != undefined) {
missingNumbersCount = arr[i+1] - arr[i] - 1;
for(j = 1; j <= missingNumbersCount; j++) {
missingNumbers.push(arr[i] + j)
}
}
}
return missingNumbers
}
findMissingNumbers(someArr) // [6, 8, 9, 11, 12, 13, 14]
Is there a better way to do this? It has to be JavaScript, since that's what I'm practicing.
You could use a sparse array with 1-values at indexes that correspond to values in the input array. Then you could create yet another array with all numbers (with same length as the sparse array), and retain only those values that correspond to an index with a 1-value in the sparse array.
This will run in O(n) time:
function findMissingNumbers(arr) {
// Create sparse array with a 1 at each index equal to a value in the input.
var sparse = arr.reduce((sparse, i) => (sparse[i]=1,sparse), []);
// Create array 0..highest number, and retain only those values for which
// the sparse array has nothing at that index (and eliminate the 0 value).
return [...sparse.keys()].filter(i => i && !sparse[i]);
}
var someArr = [2, 5, 3, 1, 4, 7, 10, 15]
var result = findMissingNumbers(someArr);
console.log(result);
NB: this requires EcmaScript2015 support.
The simplest solution to this problem
miss = (arr) => {
let missArr=[];
let l = Math.max(...arr);
let startsWithZero = arr.indexOf(0) > -1 ? 0 : 1;
for(i = startsWithZero; i < l; i++) {
if(arr.indexOf(i) < 0) {
missArr.push(i);
}
}
return missArr;
}
miss([3,4,1,2,6,8,12]);
Something like this will do what you want.
var X = [2, 5, 3, 1, 4, 7, 10, 15]; // Array of numbers
var N = Array.from(Array(Math.max.apply(Math, X)).keys()); //Generate number array using the largest int from X
Array.prototype.diff = function(a) {
return this.filter(function(i) {return a.indexOf(i) < 0;}); //Return the difference
};
console.log(N.diff(X));
Option 1:
1. create a binary array
2. iterate over input array and for each element mark binary array true.
3. iterate over binary array and find out numbers of false.
Time complexity = O(N)
Space complexity = N
Option 2:
Sort input array O(nLogn)
iterate over sorted array and identify missing number a[i+1]-a[i] > 0
O(n)
total time complexity = O(nlogn) + O(n)
I think the best way to do this without any iterations for a single missing number would be to just use the sum approach.
const arr=[1-100];
let total=n*(n+1)/2;
let totalarray=array.reduce((t,i)=>t+i);
console.log(total-totalarray);
You can try this:
let missingNum= (n) => {
return n
.sort((a, b) => a - b)
.reduce((r, v, i, a) =>
(l => r.concat(Array.from({ length: v - l - 1 }, _ => ++l)))(a[i - 1]),
[]
)
}
console.log(missingNum([1,2,3,4,10]));
Solution to find missing numbers from unsorted array or array containing duplicate values.
Array.prototype.max = function() {
return Math.max.apply(null, this);
};
var array1 = [1, 3, 4, 7, 9];
var n = array1.length;
var totalElements = array1.max(); // Total count including missing numbers. Can use max
var d = new Uint8Array(totalElements)
for(let i=0; i<n; i++){
d[array1[i]-1] = 1;
}
var outputArray = [];
for(let i=0; i<totalElements; i++) {
if(d[i] == 0) {
outputArray.push(i+1)
}
}
console.log(outputArray.toString());
My solution uses the same logic as trincot's answer
The time complexity is O(n)
const check_miss = (n) => {
let temp = Array(Math.max(...n)).fill(0);
n.forEach((item) => (temp[item] = 1));
const missing_items = temp
.map((item, index) => (item === 0 ? index : -1))
.filter((item) => item !== -1);
console.log(missing_items);
};
n = [5, 4, 2, 1, 10, 20, 0];
check_miss(n);

search for matching values in two arrays with repeated values in javascript

I have two arrays:
a = [2,2,3,0,6]
b = [6,3,2,2,0]
I am trying use for loop to match values and get the index of a in a new array c. How can we do this? Notice that there are multiple values which match and so I think the previous match must be skipped.
This is a proposal which respects the last index and looks further.
How it works:
It uses Array#map for iterating array b with a callback. map gets an own this space with an really empty object Object.create(null).
The callback has on parameter bb which is one element of `b.
Next is to find the element is in array a with a Array#indexOf and a fromIndex, based on the former searches. The former index is stored in the this object, as long as the result is not -1, because this would reset the fromIndex to zero.
If there is no this[bb] or a falsy value of this[bb] take zero as fromIndex.
Later, a found index is incremented and stored in this[bb].
At least, the index is returned.
var a = [2, 2, 3, 0, 6],
b = [6, 3, 2, 2, 0],
c = b.map(function (bb) {
var index = a.indexOf(bb, this[bb] || 0);
if (index !== -1) {
this[bb] = index + 1;
}
return index;
}, Object.create(null));
console.log(c);
Another solution could be first generate an object with all indices of a and use it in the iteration of b for returning the indices.
The example is a bit extended, to show what happen if there is no more than two indices (2) and one without being in a (7).
The content of aObj with all indices of a:
{
"0": [3],
"2": [0, 1],
"3": [2],
"6": [4]
}
var a = [2, 2, 3, 0, 6],
b = [6, 3, 2, 2, 0, 7, 2],
aObj = Object.create(null),
c;
a.forEach(function (aa, i) {
aObj[aa] = aObj[aa] || [];
aObj[aa].push(i);
});
c = b.map(function (bb) {
return aObj[bb] && aObj[bb].length ? aObj[bb].shift() : -1;
});
console.log(c);
As far I Understand, You can try this:
var a = [2,2,3,0,6];
var b = [6,3,2,2,0];
var c = new Array();
for(i = 0; i < b.length; i++)
{
for(j = 0; j < a.length; j++)
{
if(b[i] === a[j] && c.indexOf(j) < 0)
{
c.push(j);
break;
}
}
}
console.log(c); // [4, 2, 0, 1, 3]
FIDDLE DEMO HERE
If I understand correct.
let c = a.map(i => b.indexOf(i))
or
var c = a.map(function(i) { return b.indexOf(i); });
loop .map function and check same value by indexOf
indexOf will return a number,representing the position where the specified search value occurs for the first time, or -1 if it never occurs
var arr = [];
a.map(function(v){
if(b.indexOf(v) > -1){
arr.push(v);
}
});
console.log(arr);
try something like this
var a = [2,2,3,0,6];
var b = [6,3,2,2,0];
var arrayLength_a = a.length;
var arrayLength_b = b.length;
var new_array=[];
for (var i = 0; i < arrayLength_a; i++)
{
for (var j = 0; j < arrayLength_b; j++)
{
if (a[i] == b[j])
{
if(new_array.indexOf(a[i]) === -1)
{
new_array.push(a[i]);
}
}
}
}

Sort Object Containing Multiple Arrays: JavaScript [duplicate]

for hours i've been trying to figure out how to sort 2 array dependently.
Let's say I have 2 arrays.
First one:
array1 = ['zzzzz', 'aaaaaa', 'ccccc'];
and the second one:
array2 = [3, 7, 1];
I sort the first one with array1.sort(); and it becomes [aaaaaa, cccccc, zzzzzz]
now what I want is that the second one becomes [7, 1, 3]
I think it's quite simple but i'm trying to implement this in something a little more complex, im new and i keep mixing up things.
Thanks
I would "zip" them into one array of objects, then sort that with a custom sort callback, then "unzip" them back into the two arrays you wanted:
var array1 = ['zzzzz', 'aaaaaa', 'ccccc'],
array2 = [3, 7, 1],
zipped = [],
i;
for(i=0; i<array1.length; ++i) {
zipped.push({
array1elem: array1[i],
array2elem: array2[i]
});
}
zipped.sort(function(left, right) {
var leftArray1elem = left.array1elem,
rightArray1elem = right.array1elem;
return leftArray1elem === rightArray1elem ? 0 : (leftArray1elem < rightArray1elem ? -1 : 1);
});
array1 = [];
array2 = [];
for(i=0; i<zipped.length; ++i) {
array1.push(zipped[i].array1elem);
array2.push(zipped[i].array2elem);
}
alert('Sorted arrays:\n\narray1: ' + array1 + '\n\narray2: ' + array2);
Here's a working fiddle.
Here's a simple function that will do the trick:
function sortTogether(array1, array2) {
var merged = [];
for(var i=0; i<array1.length; i++) { merged.push({'a1': array1[i], 'a2': array2[i]}); }
merged.sort(function(o1, o2) { return ((o1.a1 < o2.a1) ? -1 : ((o1.a1 == o2.a1) ? 0 : 1)); });
for(var i=0; i<merged.length; i++) { array1[i] = merged[i].a1; array2[i] = merged[i].a2; }
}
Usage demo (fiddle here):
var array1 = ['zzzzz', 'aaaaaa', 'ccccc'];
var array2 = [3, 7, 1];
console.log('Before..: ',array1,array2);
sortTogether(array1, array2); // simply call the function
console.log('After...: ',array1,array2);
Output:
Before..: ["zzzzz", "aaaaaa", "ccccc"] [3, 7, 1]
After...: ["aaaaaa", "ccccc", "zzzzz"] [7, 1, 3]
Instead of two arrays of primitive types (strings, numbers) you can make an array of objects where one property of the object is string (containing "aaaaa", "cccccc", "zzzzzz") and another is number (7,1,3). This way you will have one array only, which you can sort by any property and the other property will remain in sync.
It just so happens I had some old code lying around that might do the trick:
function arrVirtualSortGetIndices(array,fnCompare){
var index=array.map(function(e,i,a){return i;});
fnCompare=fnCompare || defaultStringCompare;
var idxCompare=function (aa,bb){return fnCompare(array[aa],array[bb]);};
index.sort(idxCompare);
return index;
function defaultStringCompare(aa,bb){
if(aa<bb)return -1;
if(bb<aa)return 1;
return 0;
}
function defaultNumericalCompare(aa,bb){
return aa-bb;
}
}
function arrReorderByIndices(array,indices){
return array.map(
function(el,ix,ar){
return ar[indices[ix]];
}
);
}
var array1 = ['zzzzz', 'aaaaaa', 'ccccc'];
var array2 = [3, 7, 1];
var indices=arrVirtualSortGetIndices(array1);
var array2sorted=arrReorderByIndices(array2,indices);
array2sorted;
/*
7,1,3
*/
Sorry, I don't do 'fors'. At least not when I don't have to.
And fiddle.
Also, an alternative fiddle that sorts the results when given an array of objects like this:
given:
var list = [
{str:'zzzzz',value:3},
{str:'aaaaa',value:7},
{str:'ccccc',value:1}
];
outputs:
[
{str: "aaaaa", value: 7},
{str: "ccccc", value: 1},
{str: "zzzzz", value: 3}
]
Assumption:
The arrays are the same length (this is implied by your question)
the contents can be compared with > and < (true in your example, but I wanted to make it clear that it was assumed here)
So then we can use an insertion sort.
var value,len = array1.length;
for (i=0; i < len; i++) {
value = array1[i];
for (j=i-1; j > -1 && array1[j] > value; j--) {
array1[j+1] = array1[j];
array2[j+1] = array2[j];
}
items[j+1] = value;
}
Using a solution found here to find the new indices after sorting an array, you can apply those indices to array2 like so.
function sortWithIndices(toSort) {
for (var i = 0; i < toSort.length; i++) {
toSort[i] = [toSort[i], i];
}
toSort.sort(function(left, right) {
return left[0] < right[0] ? -1 : 1;
});
toSort.sortIndices = [];
for (var j = 0; j < toSort.length; j++) {
toSort.sortIndices.push(toSort[j][2]);
toSort[j] = toSort[j][0];
}
return toSort;
}
var array1 = ['zzzz', 'aaaa', 'cccc'];
var array2 = [3, 7, 1];
// calculate the indices of array1 after sorting. (attached to array1.sortIndices)
sortWithIndices(array1);
// the final array after applying the sorted indices from array1 to array2
var final = [];
// apply sorted indices to array2
for(var i = 0; i < array1.sortIndices.length; i++)
final[i] = array2[array1.sortIndices[i]];
// output results
alert(final.join(","));
JSFiddle Demo

indexes around a range of values

Considering a sorted array arr
1- Simple case:
var arr = [3, 6, 12, 18];
indexesAround(6)
//> [1, 1]
indexesAround(7)
//> [1, 2]
2- More complex case:
var arr = [3, 3, 6, 6, 18, 18];
indexesAround(6)
//> [2, 3]
indexesAround(7)
//> [3, 4]
How would you implement(or pseudo code) a such indexesAround(value) function ?
--
Here is what I have for now, but I think this could be enhanced:
function indexesAround(val) {
var lower = 0;
var upper = lower;
var el;
for (var i = 0, len = arr.length; i < len; i++) {
el = arr[i];
if (el > val) {break;}
if (arr[lower] < el) {lower = upper = i;}
if (arr[upper] <= el) {upper = i;}
}
return [lower, upper];
}
Considering the array is sorted:
function indexesAround(arr, val) {
if (!~arr.indexOf(val)) return false; // not found
var start = arr.indexOf(val);
var end = (arr.length - 1) - arr.reverse().indexOf(val);
arr.reverse(); // restore original order
return [start, end];
}
This solution covers every possibility and works exactly to OP's specifications. Run it on jsfiddle.
Code
function indexesAround(target,array) {
var start;
var len = array.length;
for(i = 0; i < len; i++) {
if (array[i] == target && !start) { start = i; }
if (array[i] > target) {
if(i == 0) { return [ 0, 0 ]; } // Target lower than array range
if(!start) { return [ i-1, i ]; } // Target inside array range but not found
return [ start, i-1 ]; // Target found
}
}
if(start) { return [ len-1, len-1 ]; } // Target higher than array range
return [ start, len-1 ]; // Target found and extends until end of array
}

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