Removing Element From Array of Arrays with Regex - javascript

I'm using regex to test certain elements in an array of arrays. If an inner array doesn't follow the desired format, I'd like to remove it from the main/outer array. The regex I'm using is working correctly. I am not sure why it isn't removing - can anyone advise or offer any edits to resolve this problem?
for (var i = arr.length-1; i>0; i--) {
var a = /^\w+$/;
var b = /^\w+$/;
var c = /^\w+$/;
var first = a.test(arr[i][0]);
var second = b.test(arr[i][1]);
var third = c.test(arr[i][2]);
if ((!first) || (!second) || (!third)){
arr.splice(i,1);
}

When you cast splice method on an array, its length is updated immediately. Thus, in future iterations, you will probably jump over some of its members.
For example:
var arr = ['a','b','c','d','e','f','g']
for(var i = 0; i < arr.length; i++) {
console.log(i, arr)
if(i%2 === 0) {
arr.splice(i, 1) // remove elements with even index
}
}
console.log(arr)
It will output:
0 ["a", "b", "c", "d", "e", "f", "g"]
1 ["b", "c", "d", "e", "f", "g"]
2 ["b", "c", "d", "e", "f", "g"]
3 ["b", "c", "e", "f", "g"]
4 ["b", "c", "e", "f", "g"]
["b", "c", "e", "f"]
My suggestion is, do not modify the array itself if you still have to iterate through it. Use another variable to save it.
var arr = ['a','b','c','d','e','f','g']
var another = []
for(var i = 0; i < arr.length; i++) {
if(i%2) {
another.push(arr[i]) // store elements with odd index
}
}
console.log(another) // ["b", "d", "f"]
Or you could go with Array.prototype.filter, which is much simpler:
arr.filter(function(el, i) {
return i%2 // store elements with odd index
})
It also outputs:
["b", "d", "f"]

Your code seems to work to me. The code in your post was missing a } to close the for statement but that should have caused the script to fail to parse and not even run at all.
I do agree with Leo that it would probably be cleaner to rewrite it using Array.prototype.filter though.
The code in your question would look something like this as a filter:
arr = arr.filter(function (row) {
return /^\w+$/.test(row[0]) && /^\w+$/.test(row[1]) && /^\w+$/.test(row[2]);
});
jsFiddle
I'm assuming it is 3 different regular expressions in your actual code, if they are all identical in your code you can save a little overhead by defining the RegExp literal once:
arr = arr.filter(function (row) {
var rxIsWord = /^\w+$/;
return rxIsWord.test(row[0]) && rxIsWord.test(row[1]) && rxIsWord.test(row[2]);
});

Related

i wanna delete array element but i have a problem

i wanna delete array element but i have a problem.
i ever looking for google, and stackOverFlow's solution but.. i can't understand well.. and
how to treat well in my code.
for example,
let str = (' a b c d C b A ')
// i wanna array like that ( ["a", "b", "c", "d", "c", "b", "a"] )
// so, first i using replace method. (Unfortunately, blocked str.trim method from academy)
// after using replace method,
let blank = str.replace(" ","")
"a b c d C b A "
// and i using split method,
let arr = blank.toLowerCase().split(" ")
// 'toLowerCase()' is need to solve next matter
and like that
["a", "", "b", "c", "d", "c", "b", "a", ""]
problem is begin,
i wanna delete "" element. but,
target an unspecified index, i cant using splice method.
maybe it need to 'for' ,
for(let i = 0 ; i < arr.length; i++) {
if(arr[i]==="") { ...i dont know what to doo.. }
}
Is my direction correct?
And what and how should we do it? i guess i cant using 'splice' method.. because of that..
You should try as code snippet
var array = ["a", "", "b", "c", "d", "c", "b", "a", ""];
var newArr = array.filter(function (el) {
return el != "";
});
console.log(newArr);
let str = (' a b c d C b A ');
let arr = str.toLowerCase().split('').filter(e=>e!=' ');
May be it what you want

Checking values of one array against another in JS

I'm trying to do a check that the first array contains the same values of the second array.
However I'm confused about my code.
First question is: why is my code running my else statement if all letters in the first array are contained in the second? it will run 2 lines of "this is not valid"
Second question is: if my first array contains a duplicate letter it will still pass the check e.g
["a", "b" , "a", "d", "e", "f"]; even though there is two a's in the first it will see the same "a" again. Anyone know a way around this.
Sorry for my long winded questions but I hope it makes sense. Thanks :)
var letters = ["a", "b" , "c", "d", "e", "f"];
var otherLetters = ["a","b", "c" , "d", "e", "f"];
var i = -1;
while(i<=letters.length){
i++;
if(otherLetters.includes(letters[i])){
console.log("This is valid");
}
else
console.log("This is not valid");
}
You didn't close the brackets. And your loop is very confusing, please use foreach. Here is a working example:
const letters = ["a", "b" , "c", "d", "e", "f"];
const otherLetters = ["a","b", "c" , "d", "e", "f"];
letters.forEach(el => {
if (otherLetters.includes(el)) {
console.log(el + 'is valid');
} else {
console.log(el + 'is not valid');
}
});
You are trying to access array elements which are out of bounds. The script runs 8 iterations over an array with 6 elements.
Nothing to worry, cpog90.
Try this solution.
var letters = ["a", "b" , "c", "d", "e", "f"];
var otherLetters = ["a","b", "c" , "d", "e", "f"];
var i = 0;
while(i<letters.length){
if(otherLetters.includes(letters[i])){
console.log("This is valid");
}
else {
console.log("This is not valid "+i);
}
i++;
}
What went wrong in your logic?
If you declare i = -1 and while(i<=letters.length), As 6 is length of letters, 8 iterations will be done as follows.
For first iteration (i = -1), 'while' condition returns true and checks for 'a'
output: This is valid
For second iteration (i = 0), 'while' condition returns true and checks for 'b'
output: This is valid
For third iteration (i = 1), 'while' condition returns true and checks for 'c'
output: This is valid
For fourth iteration (i = 2), 'while' condition returns true and checks for 'd'
output: This is valid
For fifth iteration (i = 3), 'while' condition returns true and checks for 'e'
output: This is valid
For sixth iteration (i = 4), 'while' condition returns true and checks for 'f'
output: This is valid
For seventh iteration (i = 5), 'while' condition returns true and checks for undefined value.
output: This is not valid
For eighth iteration (i = 6), 'while' condition returns true and checks for undefined value.
output: This is not valid
First of all you have set i = -1 which is confusing since array start position is 0.
The reason your loop is running two extra times is because loop started at -1 instead of 0 and next the condition i <= length.
Since [array length = last index + 1] your loop runs extra two times.
Just to make your code work assign var i = 0 and while condition i < letters.length
Simplest solution is using lodash. It has all optimizations out-of-the-box:
var letters = ["a", "b" , "c", "d", "e", "f"];
var otherLetters = ["f", "a","b", "c" , "d", "e"];
const finalLetters = _.sortBy(letters);
const finalOtherLetters = _.sortBy(otherLetters);
if (_.isEqual(finalLetters, finalOtherLetters)) {
console.log('Two arrays are equal.');
} else {
console.log('Two arrays are not equal.');
}
<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.15/lodash.min.js"></script>
Arrays are index based and starts from 0. So, the -1 and the less than letters.length check puts the code into out of bounds.
var letters = ["a", "b" , "c", "d", "e", "f"];
var otherLetters = ["a","b", "c" , "d", "e", "f"];
var i = 0;
while(i<letters.length)
{
if(otherLetters.includes(letters[i]))
{
console.log("This is valid");
}
else
{
console.log("This is not valid");
}
i++;
}
You can use a combination of Array.prototype.every with Array.prototype.includes, along with some extra guard clauses.
const areSequenceEqual = (arr1, arr2) => {
if (!arr1 || !arr2) {
return false;
}
if (arr1.length !== arr2.length) {
return false;
}
return arr1.every(x => arr2.includes(x));
};
const letters = ["a", "b", "c", "d", "e", "f"];
const otherLetters = ["a", "b", "c", "d", "e", "f"];
const someOtherLetters = ["a", "b", "c", "d", "e", "f", "g"];
console.log(areSequenceEqual(letters, otherLetters));
console.log(areSequenceEqual(letters, undefined));
console.log(areSequenceEqual(letters, someOtherLetters));

Function to reiterate values in an array using Javascript

I need to create a function that inputs a new value into an empty array, and then the value stays in the array, even if the value changes. Let me explain with an example and I have so far:
var arr = [];
arr.unshift("f");
if (arr.length > 6) {
arr.pop();
}
console.log(arr);
arr.unshift("e");
if (arr.length > 6) {
arr.pop();
}
console.log(arr);
arr.unshift("d");
if (arr.length > 6) {
arr.pop();
}
console.log(arr);
arr.unshift("c");
if (arr.length > 6) {
arr.pop();
}
console.log(arr);
arr.unshift("b");
if (arr.length > 6) {
arr.pop();
}
console.log(arr);
arr.unshift("a");
if (arr.length > 6) {
arr.pop();
}
console.log(arr);
arr.unshift("z");
if (arr.length > 6) {
arr.pop();
}
console.log(arr);
Here in the empty array a new value gets inputted in first position and stays in the array arr. This is what I get in the console:
(6) ["f"]
(6) ["e", "f"]
(6) ["d", "e", "f"]
(6) ["c", "d", "e", "f"]
(6) ["b", "c", "d", "e", "f"]
(6) ["a", "b", "c", "d", "e", "f"]
(6) ["z", "a", "b", "c", "d", "e"]
which is exactly what I want to achieve. Instead of these values I need a var that will get updated regularly.
var newValue = value_to_be_updated;
function myFunction(newValue) {
var arr = [];
arr.unshift(newValue);
return arr
}
if (arr.length > 6) {
arr.pop();
}
My goal is to reduce the above code and make it a function, but couldn't find anything helpful. Also is there any way the value inputted stays in the array, even if removed from the var?
Any help will be hugely appreciated!!!!!
Thanks in advance
You should be getting the new value dynamically using for example a prompt, if you are expecting the value of arr to remain the same after changing the source code that would not work.
Still has #gurvinder372 said your function should look something like this
var arr = [];
function myFunction(newValue) {
arr.unshift(newValue);
if (arr.length > 6) {
arr.pop();
}
return arr
}
then to use it you can do something like this
for (var i = 0; i<8; i++){
var value = prompt('enter char');
myFunction(value);
}

How to iterate a list reversely and stop with a condition with lodash?

I have a list with some items for example
["a", "b", "c", ..., "x", "y", "z"]
I would like to iterate it but from the end to beggining and push those items into a new variable, and stop when it has length == 3.
For that simple example I would like to have as result within my new var:
["z", "y", "x"]
I'm thinking of .reverse() my array and then iterate it with .each and push my items, but I believe there is a better way to do that with lodash, that I'm not finding.
Maybe I'm not knowing how to search.
Thanks in advance.
You can do it with the function "_.takeRightWhile" from lodash like the code below:
var arr = ["a", "b", "c", "x", "y", "z"];
var reverseArray = [];
_.takeRightWhile(arr, function(item){
reverseArray.push(item)
return reverseArray.length < 3
});
console.log(reverseArray);
<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.4/lodash.min.js"></script>
In plain Javascript you could use Array#slice with a negative count for getting a new array from the end and use Array#reverse for a reversed array.
var array = ["a", "b", "c", "x", "y", "z"],
result = array.slice(-3).reverse();
console.log(result);
For processing items, you could use Array#reduceRight.
var array = ["a", "b", "c", "x", "y", "z"],
result = array.slice(-3).reduceRight((r, a) => r.concat(a), []);
console.log(result);
Another solution that iterates the original array:
var arr = ["a", "b", "c", "x", "y", "z"], res=[], count=3;
if (count <= arr.length)
for (var i=0; i<count; i++) res.push(arr[arr.length-1-i]);
console.log(res);

2D Array to JsTree compatible JSON

I currently have a javascript function that accepts 1 dimensional arrays and adds them to a tree object.
var tree = {}
function addToTree(tree, arr) {
for (var i = 0, length = arr.length; i < length - 1; i++) {
tree = tree[arr[i]] = tree[arr[i]] || {};
}
tree[arr[i]] = null;
}
addToTree(tree, ["a", "b", "c", "f"])
addToTree(tree, ["a", "b", "d", "h", "l"])
I was hoping someone could help me format it so that it returns the object into a JSTree compatible object found here: https://www.jstree.com/docs/json/
For each element in the array ["a", "b", "c", "f"] you first need to create a node (one compatible to JSTree) and then add that node to the json object tree which we are building.
function createTreeNode(value) {
return {'text': value};
}
Now the function addToTree can be
var tree = {'core': {'data': []}}; //This initialization is needed
function addToTree(tree, arr) {
for (var i = 0; i < arr.length; i++) {
node = createTreeNode(arr[i]);
tree.core.data.push(node);
}
}
addToTree(tree, ["a", "b", "c", "f"]);
addToTree(tree, ["a", "b", "d", "h", "l"]);
BTW: In case you are using BootStrap consider jonmiles tree

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