How to remove items from list that were pushed - javascript

I am trying to remove only items that were pushed into a list so that I am only left with the original list items
const list = ["a", "b", "c", "d"];
for (let i = 0; i < 4; i++) {
list.push(i);
}
console.log(list);
// outputs: a,b,c,d,1,2,3,4 // as expected
// how can we remove only the pushed items.
list.pop;
console.log(list);
// outputs : []
// desired output: a,b,c,d

I'm not sure what your case is and why you want to extract the items from the array but anyway.
The first option would be: duplicating the array into another variable
or the second option: extracting it using splice when you know the length of the original array.
Snippets:
const list = ["a", "b", "c", "d"];
const original = list.slice(); // duplicating array
const originalLength = list.length // getting original length
for (let i = 0; i < 4; i++) {
list.push(i);
}
console.log("original1: ", original);
console.log("original2: ", list.slice(0, originalLength));

You can remove the elements from the index where you have begun pushing new elements using splice.
const list = ["a", "b", "c", "d"];
for (let i = 0; i < 4; i++) {
list.push(i);
}
list.splice(list.length - 4)
console.log(list);

If you need two to have one "for loop" pushing items into an array, and then remove those same items in another loop, then a simple solution would be
Snippet:
const list = ["a", "b", "c", "d"];
for (let i = 0; i < 4; i++) {
list.push(i);
}
for (let j of list) {
if (j) {
list.pop();
}
};
console.log(list);

Related

why is the value of b incrementing on its own after 2nd iteration?

i am just playing with arrays in this code the value of b is increasing even though the code doesnt gets into the if block?
function chunkArrayInGroups(arr, size) {
// Break it up.
let ar = [];
let b = [];
for (let i = 0; i < arr.length; i++) {
ar.push(arr[i]);
console.log(b, i);
if ((i + 1) % size == 0) {
b.push(ar);
}
}
return arr;
}
console.log(chunkArrayInGroups(["a", "b", "c", "d"], 2));
expected:[],0
[],1
[a,b],2
[a,b],3
obtained:[],0
[],1
[a,b,c],2
[a,b,c,d],3
Because when you use b.push(ar), you push the address not the value of ar. So when ar change, b also change. To get your expected output, you should use b.push(...ar), it will create a clone of ar.
Demo:
function chunkArrayInGroups(arr, size) {
// Break it up.
let ar=[];
let b=[];
for(let i=0;i<arr.length;i++)
{
ar.push(arr[i]);
console.log(b,i);
if((i+1)%size==0)
{
b.push(...ar);
}
}
return arr;
}
chunkArrayInGroups(["a", "b", "c", "d"], 2);

nested for each loop to insert value which in array without duplication and loop start from first

Example
If my values are in array like this
var myPlaces = ["a", "b", "c"];
var friendPlaces = ["d", "0", "e"];
for(var i = 0; i < myPlaces.length; i++) {
console.log(myPlaces[i]);
for(var j = 0; j < friendPlaces.length; j++) {
if (myPlaces[i] == friendPlaces[i]) {
console.log(myPlaces[i]);
};
I need answer as
(a,d)(b,0)(c,e) as three result but it gives count more than 3
help me to modify my current answer (a,d) (d,a) (d,b) (d,c) then (b,o)
You can use Array#map (Assuming your input arrays are of same length with fixed count of arrays- i.e. 2 in your case).
If you use map on myPlaces then 1st parameter is current value of myPlaces in loop and the 2nd parameter is index of that element in array. So you can match current element in myPlaces with elements from friendPlaces array with the same index using this index.
var myPlaces = ["a", "b", "c"];
var friendPlaces = ["d", "0", "e"];
var result = myPlaces.map((e, i) => "("+e +","+ friendPlaces[i]+")");
console.log(result);

How to remove element from array using javascript

I have 2 array and want to remove the elements of 2nd array as per position numbers on 1st array.
var notexists = []; //value is "1","5","8" on 0,1,2nd position.
var copyrequiredfields = [];//Value is "a","b","c","d","e","f",...
for (var i = 0; i < notexists.length; i++) {
copyrequiredfields.splice(parseInt(notexists[i]), 1);
}
as per example i want to remove 1st 5th and 8th element from copyrequiredfields .
Please suggest some answer.
Create a new array, iterate the copyrequiredfields, when the index in notexists, ignore it.
example:
var notexist = [1,2,5];
var copyrequiredfields = ['a','b','c','d','e','f','g'];
//create a index map
var index_map = {};
for(var i = 0; i < notexist.length; i++){
index_map[notexist[i]] = true;
}
//remove the elements
var newarray = [];
for(var i = 0; i < copyrequiredfields.length; i++){
if(!index_map[i]){
newarray.push(copyrequiredfields[i]);
}
}
copyrequiredfields = newarray;
In JS, index of array starts with 0 and not 1 so you just have to subtract 1 from value before splice. Rest of the code is fine.
One issue is, as you remove elements from array, elements after it are moved 1 position back. This will give you incorrect output. 1 hack is to count number of elements removed to count movement.
A better solution would be to use array.filter.
Array.splice
var notexists = ["1", "5", "8"]; //value is on 0,1,2nd position.
var copyrequiredfields = ["a", "b", "c", "d", "e", "f", "g", "h", "i"]; //Value is "a","b","c","d","e","f",...
var count=0;
for (var i = 0; i < notexists.length; i++) {
console.log(+notexists[i] - 1)
copyrequiredfields.splice(+notexists[i]-1-count++, 1);
}
console.log(copyrequiredfields)
Array.filter
var notexists = ["1", "5", "8"]; //value is on 0,1,2nd position.
var copyrequiredfields = ["a", "b", "c", "d", "e", "f", "g", "h", "i"]; //Value is "a","b","c","d","e","f",...
var r = copyrequiredfields.filter((x,i)=>notexists.indexOf((i+1).toString()) === -1)
console.log(r)
You could copy the whole array, except of the parts you dont need anymore:
var tempCopy = [];
for (var i=0; i < copyrequiredfields.length; i++)
if(notexists.indexOf(i)==-1)
tempCopy.push(copyrequiredfields[i]);
copyrequiredfields = tempCopy;
Greets!

Remove duplicates of single "a" value from array if array has multiple "a" elements

I am looking for a simple solution. I have an array like array("a","b","c","a","g");
Now when i try splice or custom remove function , it removes all "a" elements from array.
What i want is when i remove "a" from the array , then the array should finally have 1 "a" element only inside it and remove all other dulicates of "a".
Now consider another case , when my array is like array("a","a","b","c","a") , then after removing "a" , the array should like array("a","b","c").
Help needed,
Thanks in advance
Try this snippet
var arr = ["a","a","b","c","a"];
var arrayLength = arr.length;
for (var i = 0; i < arrayLength; i++) {
for (var j = i + 1; j < arrayLength;) {
if (arr[j] == arr[i]) {
for (var k = j; k < arrayLength; k++) {
arr[k] = arr[k + 1];
}
arrayLength--;
} else
j++;
}
}
var newArr = [];
for (var i = 0; i < arrayLength; i++) {
newArr.push(arr[i]);
}
console.log(newArr);
You can make use of the filter method like:
var duplicates = ["a","a","b","c","a"];
var withoutDuplicates = duplicates.filter(function(currentValue, index) {
return duplicates.indexOf(currentValue) == index;
});
console.log(withoutDuplicates); // Array [ "a", "b", "c" ]
As also stated here:
Remove Duplicates from JavaScript Array
Documentation: http://www.w3schools.com/jsref/jsref_filter.asp
You could use Set and keep only unique items in the array.
var unique = array => array.filter((set => a => !set.has(a) && set.add(a))(new Set));
console.log(unique(["a", "b", "c", "a", "g"]));
console.log(unique(["a", "a", "b", "c", "a"]));
Different style
var unique = function (array) {
return array.filter(function (a) {
if (!this.has(a)) {
this.add(a);
return true;
}
}, new Set);
};
console.log(unique(["a", "b", "c", "a", "g"]));
console.log(unique(["a", "a", "b", "c", "a"]));
ES5 with Object as hash
var unique = function (array) {
return array.filter(function (a) {
if (!this[a]) {
return this[a] = true;
}
}, Object.create(null));
};
console.log(unique(["a", "b", "c", "a", "g"]));
console.log(unique(["a", "a", "b", "c", "a"]));
Can try this one
var array = ["a","a","b","c","a"];
var filterIfMultiple = function (data) {
var count = 0;
array = array.filter(function(val) {
if (val === data) count+=1;
if(val !== data || (val === data && count <= 1)){
return val;
}
});
};
filterIfMultiple("a");
console.log(array);
Another process without passing any parameter using ES6 Set object
var array = ["a","a","b","c","a","b"];
function filterIfDuplicate() {
array = Array.from(new Set(array));
}
filterIfDuplicate();
console.log(array);

How might I return multiple arrays with equal values from a larger array with mixed values?

I have an array that after being sorted appears like this:
var arr = ["a", "a", "b", "b", "b", "b", "c", "c", "c"];
There are 2 "a" Strings, 4 "b" Strings, and 3 "c" Strings.
I am trying to return 3 separate arrays, returning them one at a time from a loop, containing only matching values. So, upon the first iteration, the returned array would appear as newArr = ["a", "a"], the second as newArr = ["b", "b", "b", "b"] and on the third iteration as newArr = ["c", "c", "c"].
However, this is a small array of predefined values, and I need an algorithm that can perform the same operation on an array of unknown size, unknown elements, and with an unknown number of like elements. (and keep in mind that the array is already sorted to begin with, in this context)
Here's my crazy code that is displaying some unusual, and incorrect, results:
var arr = ["a", "a", "b", "b", "b", "b", "c", "c", "c"];
for(var index = 0; index < arr.length; index++)
{
var test = "";
var newArr = []; // resets the new array upon each iteration
var str = arr[index]; // initialized as the next unique index-value
for(var i = index; i < arr.length; i++)
{
if(arr[i] == str)
{
newArr.push(arr[k]);
test += arr[i] + " ";
}
else
{
index = i; // changing the outer loop variable
break; // exiting the inner loop
}
} // end of inner loop
window.alert(test);
setValues(newArr);
} // end of outer loop
function setValues(arrSorted)
{
var here = document.getElementById("here");
for(var i = 0; i < arrSorted.length; i++)
{
here.innerHTML += arrSorted[i] + " ";
}
here.innerHTML += "<br />";
} // end of setValues function
var arr = ["a", "a", "b", "b", "b", "b", "c", "c", "c"];
var arrays = {};
for (var i=0;i<arr.length;i++) {
if (!arrays[arr[i]]) arrays[arr[i]] = [];
arrays[arr[i]].push(arr[i]);
}
this will give you the equivalent of
arrays = {};
arrays['a'] = ['a','a'];
arrays['b'] = ['b','b','b','b','b'];
arrays['c'] = ['c','c','c'];
You can use a function like this to divide the array into several arrays:
function divide(arr) {
var subArrays = [];
var current = null;
var subArray = null;
for (var i = 0; i < arr.length; i++) {
if (arr[i] != current) {
if (subArray != null) subArrays.push(subArray);
current = arr[i];
subArray = [];
}
subArray.push(arr[i]);
}
if (subArray != null) subArrays.push(subArray);
return subArrays;
}
Demo: http://jsfiddle.net/Guffa/d8CBD/
This is how I would do it:
var arr = ["a", "a", "b", "b", "b", "b", "c", "c", "c"];
var out = [], prev;
for (var i = 0, j = 0, len = arr.length; i < len; i++) {
if (arr[i] !== prev || !out.length) {
out[j++] = [prev = arr[i]];
} else {
out[j - 1].push(prev);
}
}
//out -> [["a","a"],["b","b","b"],["c","c","c"]]
Demo
Note: the || !out.length check is just handle arrays that start with undefined correctly, but feel free to remove it if this will never be the case

Categories