Let's say I have the following string: "Stackoverflow", and I want to insert a space between every third number like this: "S tac kov erf low" starting from the end. Can this be done with regexes?
I have done it the following way with a for-loop now:
var splitChars = (inputString: string) => {
let ret = [];
let counter = 0;
for(let i = inputString.length; i >= 0; i --) {
if(counter < 4) ret.unshift(inputString.charAt(i));
if(counter > 3){
ret.unshift(" ");
counter = 0;
ret.unshift(inputString.charAt(i));
counter ++;
}
counter ++;
}
return ret;
}
Can I shorten this is some way?
You could take a positive lookahead and add spaces.
console.log("StackOverflow".replace(/.{1,3}(?=(.{3})+$)/g, '$& '));
You can use Regex to chunk it up and then join it back together with a string.
var string = "StackOverflow";
var chunk_size = 3;
var insert = ' ';
// Reverse it so you can start at the end
string = string.split('').reverse().join('');
// Create a regex to split the string
const regex = new RegExp('.{1,' + chunk_size + '}', 'g');
// Chunk up the string and rejoin it
string = string.match(regex).join(insert);
// Reverse it again
string = string.split('').reverse().join('');
console.log(string);
This is a solution without regexp, with a for...of
<!DOCTYPE html>
<html>
<body>
<script>
const x="Stackoverflow",result=[];
let remaind = x.length %3 , ind=0 , val;
for(const i of x){
val = (++ind % 3 === remaind) ? i+" " : i;
result.push(val);
}
console.log(result.join(''));
</script>
</body>
</html>
Related
I need to implement the .split method in my own way without using prebuilt functions. The method should receive a string divided into 2 sentences by a dot and divide them through a separator.
For example, there is this string:
'word wooord wooooooooord wooooooord. wooooooooord woooooord woooord wooooooooord', separator in this case: '. '
The result should be:
['word wooord wooooooooord wooooooord", "wooooooooord woooooord woooord wooooooooord']
I tried to implement it myself, the first problem I encountered is that the words from the string are added character by character to the new array. The second problem is that the output is still a string even though I declared an array earlier.
function split(str, splitter){
let arrSent = []
for (let i = 0; i < str.length; i++){
if (str[i] != splitter){
arrSent += str[i]
}
}
return arrSent
}
console.log(split('word wooord wooooooooord wooooooord. wooooooooord woooooord woooord wooooooooord', '. '))
Since the delimiter can have more than one character, you need a system to upfront collect a sample of characters (of the same length as the delimiter) to be then compared with the delimiter:
const split = (str, delimiter) => {
// If delimiter is empty string just return an array of characters
if (delimiter === "") return [...str];
const len = delimiter.length;
const iter = str.length - len + 1; // max needed iterations
const arr = [""]; // Prefill it with empty string
let idx = 0; // arr insertion pointer
for (let i = 0; i < iter; i++) {
// Collect len chars from str as a sample
// to compare with the delimiter:
let sample = "";
for (let x = i; x < i + len; x++) {
sample += str[x];
}
const isSplit = sample === delimiter;
const isEnded = i === iter - 1;
if (isSplit) {
i += len - 1; // Consume splitted characters
idx += 1; // Increment arr pointer
arr[idx] = ""; // Prepare the new array key as empty string
} else {
// If loop ended append the entire sample.
// Otherwise, append a single character:
arr[idx] += isEnded ? sample : str[i];
}
}
return arr
}
console.log(split("word. etc", ". "));
console.log(split("word. etc. ", ". "));
console.log(split(". word yep. . etc. ", ". "));
console.log(split("word", ". "));
console.log(split("word", "word"));
console.log(split("word", ""));
console.log(split("", ""));
above, idx (starting at 0) is used as the output's arr insertion pointer. The idx is incremented if the sample matches the delimiter. Also, if there's a match, we need to skip iterations i += len, to not include the delimiter in the output array.
To test, create many examples and right before return arr; use console.log(JSON.stringify(arr) === JSON.stringify(str.split(delimiter))); - it should return true for all the submitted tests.
I'm trying to figure out how to remove every second character (starting from the first one) from a string in Javascript.
For example, the string "This is a test!" should become "hsi etTi sats!"
I also want to save every deleted character into another array.
I have tried using replace method and splice method, but wasn't able to get them to work properly. Mostly because replace only replaces the first character.
function encrypt(text, n) {
if (text === "NULL") return n;
if (n <= 0) return text;
var encArr = [];
var newString = text.split("");
var j = 0;
for (var i = 0; i < text.length; i += 2) {
encArr[j++] = text[i];
newString.splice(i, 1); // this line doesn't work properly
}
}
You could reduce the characters of the string and group them to separate arrays using the % operator. Use destructuring to get the 2D array returned to separate variables
let str = "This is a test!";
const [even, odd] = [...str].reduce((r,char,i) => (r[i%2].push(char), r), [[],[]])
console.log(odd.join(''))
console.log(even.join(''))
Using a for loop:
let str = "This is a test!",
odd = [],
even = [];
for (var i = 0; i < str.length; i++) {
i % 2 === 0
? even.push(str[i])
: odd.push(str[i])
}
console.log(odd.join(''))
console.log(even.join(''))
It would probably be easier to use a regular expression and .replace: capture two characters in separate capturing groups, add the first character to a string, and replace with the second character. Then, you'll have first half of the output you need in one string, and the second in another: just concatenate them together and return:
function encrypt(text) {
let removedText = '';
const replacedText1 = text.replace(/(.)(.)?/g, (_, firstChar, secondChar) => {
// in case the match was at the end of the string,
// and the string has an odd number of characters:
if (!secondChar) secondChar = '';
// remove the firstChar from the string, while adding it to removedText:
removedText += firstChar;
return secondChar;
});
return replacedText1 + removedText;
}
console.log(encrypt('This is a test!'));
Pretty simple with .reduce() to create the two arrays you seem to want.
function encrypt(text) {
return text.split("")
.reduce(({odd, even}, c, i) =>
i % 2 ? {odd: [...odd, c], even} : {odd, even: [...even, c]}
, {odd: [], even: []})
}
console.log(encrypt("This is a test!"));
They can be converted to strings by using .join("") if you desire.
I think you were on the right track. What you missed is replace is using either a string or RegExp.
The replace() method returns a new string with some or all matches of a pattern replaced by a replacement. The pattern can be a string or a RegExp, and the replacement can be a string or a function to be called for each match. If pattern is a string, only the first occurrence will be replaced.
Source: String.prototype.replace()
If you are replacing a value (and not a regular expression), only the first instance of the value will be replaced. To replace all occurrences of a specified value, use the global (g) modifier
Source: JavaScript String replace() Method
So my suggestion would be to continue still with replace and pass the right RegExp to the function, I guess you can figure out from this example - this removes every second occurrence for char 't':
let count = 0;
let testString = 'test test test test';
console.log('original', testString);
// global modifier in RegExp
let result = testString.replace(/t/g, function (match) {
count++;
return (count % 2 === 0) ? '' : match;
});
console.log('removed', result);
like this?
var text = "This is a test!"
var result = ""
var rest = ""
for(var i = 0; i < text.length; i++){
if( (i%2) != 0 ){
result += text[i]
} else{
rest += text[i]
}
}
console.log(result+rest)
Maybe with split, filter and join:
const remaining = myString.split('').filter((char, i) => i % 2 !== 0).join('');
const deleted = myString.split('').filter((char, i) => i % 2 === 0).join('');
You could take an array and splice and push each second item to the end of the array.
function encrypt(string) {
var array = [...string],
i = 0,
l = array.length >> 1;
while (i <= l) array.push(array.splice(i++, 1)[0]);
return array.join('');
}
console.log(encrypt("This is a test!"));
function encrypt(text) {
text = text.split("");
var removed = []
var encrypted = text.filter((letter, index) => {
if(index % 2 == 0){
removed.push(letter)
return false;
}
return true
}).join("")
return {
full: encrypted + removed.join(""),
encrypted: encrypted,
removed: removed
}
}
console.log(encrypt("This is a test!"))
Splice does not work, because if you remove an element from an array in for loop indexes most probably will be wrong when removing another element.
I don't know how much you care about performance, but using regex is not very efficient.
Simple test for quite a long string shows that using filter function is on average about 3 times faster, which can make quite a difference when performed on very long strings or on many, many shorts ones.
function test(func, n){
var text = "";
for(var i = 0; i < n; ++i){
text += "a";
}
var start = new Date().getTime();
func(text);
var end = new Date().getTime();
var time = (end-start) / 1000.0;
console.log(func.name, " took ", time, " seconds")
return time;
}
function encryptREGEX(text) {
let removedText = '';
const replacedText1 = text.replace(/(.)(.)?/g, (_, firstChar, secondChar) => {
// in case the match was at the end of the string,
// and the string has an odd number of characters:
if (!secondChar) secondChar = '';
// remove the firstChar from the string, while adding it to removedText:
removedText += firstChar;
return secondChar;
});
return replacedText1 + removedText;
}
function encrypt(text) {
text = text.split("");
var removed = "";
var encrypted = text.filter((letter, index) => {
if(index % 2 == 0){
removed += letter;
return false;
}
return true
}).join("")
return encrypted + removed
}
var timeREGEX = test(encryptREGEX, 10000000);
var timeFilter = test(encrypt, 10000000);
console.log("Using filter is faster ", timeREGEX/timeFilter, " times")
Using actually an array for storing removed letters and then joining them is much more efficient, than using a string and concatenating letters to it.
I changed an array to string in filter solution to make it the same like in regex solution, so they are more comparable.
I have two strings. The first is normal string, the second I want to be a reversed string like first one, but in the console I didn't get the look of like first one listed by commas. How can I fix that ?
Normal string -
Revered string -
window.onload = function(){
inputBox = document.getElementById("myText");
btn = document.getElementById('sub');
btn.addEventListener("click",function(event){
event.preventDefault();
findPalindromes(inputBox.value);
});
str = inputBox.value;
function findPalindromes(str) {
var words = str.split(" ");
for (var i = 0; i < words.length - 1; i++) {
words[i] += " ";
}
console.log(words);
var newString = "";
for (var i = words.length - 1; i >= 0; i--) {
newString += words[i];
}
console.log(newString);
}
}
If you really just want to find out if a string is a palindrome, you can do something as simple as this:
function isPalindrome(str) {
return str.toLowerCase() === str.toLowerCase().split('').reverse().join('');
}
The first for loop is not necessary. You do not need to concatenate a space character " " to the element of the array, where the variable assignment i
var i = 0;
and condition
i < words.length - 1;
stops before reaching last element of array.
var newString = "";
for (var i = words.length - 1; i >= 0; i--) {
newString += words[i] + " ";
}
console.log(newString);
In your "normal" string example, you're printing words to the console. Let's first look at what words is: var words = str.split(" ");
The String.split() function returns an array of strings. So your "normal" string is actually an array of strings (The brackets [] and comma separated strings in the console output indicate this).
In the second example, you're logging newString. Let's look at where it comes from: var newString = "";
newString is a String. If you want it to be an array of strings like words, you would declare it with var newString = [];. Arrays do not support += so newString += words[i]; would become newString.push(words[i]);
The above explains how to get newString to behave like words, the code you've written is not looking for a palindrome word, but rather a palindrome sentence: "Bob is Bob" is not a palindrome (reversed it is "boB si boB") but it could be a Palindrome sentence (if such a thing exists).
Thanks to all, I wrote this solution for the problem. I hope this is the right answer.
window.onload = function(){
inputBox = document.getElementById("myText");
btn = document.getElementById('sub');
btn.addEventListener("click",function(event){
event.preventDefault();
findPalindromes(inputBox.value);
});
str = inputBox.value;
function findPalindromes(str) {
var words = str.split(" "),
newString = [];
for (var i = 0; i < words.length - 1; i++) {
if ((words[i] === words[i].split('').reverse().join('')) === true) {
newString.push(words[i]);
}
}
console.log(newString);
}
}
var words = " ";
function reverse_arr(arr){
var i = arr.length - 1;
while(i >= 0){
words += a[i] + " ";
i--;
}
return words;
}
Can anyone shed light on how to frame a javascript function with two parameters: string and character, and only by using the slice method, return the number of times "a" appears in "lava"?
without slice method
var fruits= "lavaaagg";
var count=0;
for(var i=0;i<fruits.length;i++){
if(fruits[i]!='a')
count++;
}
console.log(fruits.length-count);
I'm not sure why you need the slice method. The slice method isn't for searching substrings (or characters in your case), it extracts a substring.
This should work fine:
function howManyCharInStr(str, char) {
return str.split(char).length - 1;
}
Step-by-step explanation:
str.split(char)
Creates an array of str substrings, using char as a separator. For example:
'fooXbazXbar'.split('X')
// Evaluates to ['foo', 'baz', 'bar']
'lorem ipsum dolor'.split('m')
// Evaluates to ['lore', ' ipsu', ' dolor']
Notice how the array returned has a length of n+1 where n is the number of separators there were. So use
str.split(char).length - 1;
to get the desired result.
For getting number of charecters count
<script type="text/javascript">
function FindResults() {
var firstvariable= document.getElementById('v1');
var secondvariable = document.getElementById('v2');
var rslt = GetCharecterCount(firstvariable, secondvariable );
}
function GetCharecterCount(var yourstring,var charecter){
var matchesCount = yourstring.split(charecter).length - 1;
}
</script>
using slice method
var arr = yourstring.split(charecter);
for( var i = 0, len = arr.length; i < len; i++ ) {
var idx = yourstring.indexOf( arr[i] );
arr[i] = pos = (pos + idx);
str = str.slice(idx);
}
var x= arr.length-1;
example http://jsfiddle.net/rWJ5x/2/
Using slice method
function logic(str,char){
var count = 0;
for(var i = 0; i < str.length; i++){
if(str.slice(i,i+1) == char){
count++;
}
}
return count;
};
console.log( "count : " + logic("lava","a") );
repeat last character of sting n number of times..
function modifyLast(str, n) {
var newstr = str.slice(-1)
var newlaststr = newstr.repeat(n-1)
var concatstring = str.concat(newlaststr);
return concatstring;
}
//modifyLast();
console.log(modifyLast("Hellodsdsds", 3))
I was messing around with the first question here: Reduce duplicate characters to a desired minimum and am looking for more elegant answers than what I came up with. It passes the test but curious to see other solutions. The sample tests are:
reduceString('aaaabbbb', 2) 'aabb'
reduceString('xaaabbbb', 2) 'xaabb'
reduceString('aaaabbbb', 1) 'ab'
reduceString('aaxxxaabbbb', 2) 'aaxxaabb'
and my solution (that passes these tests):
reduceString = function(str, amount) {
var count = 0;
var result = '';
for (var i = 0; i < str.length; i++) {
if (str[i] === str[i+1]) {
count++;
if (count < amount) {
result += str[i];
}
} else {
count = 0;
result += str[i];
}
};
return result;
}
Just use regular expressions.
var reduceString = function (str, amount) {
var re = new RegExp("(.)(?=\\1{" + amount + "})","g");
return str.replace(re, "");
}
I guess my best solution would be like
var str = "axxxaabbbbcaaxxxaab",
redStr = (s,n) => s.replace(/(\w)\1+/g,"$1".repeat(n));
console.log(redStr(str,2));
I tried to make it as short as possible:
reduceString = function(str, amount) {
var finalString = '', cL = '', counter;
str.split('').forEach(function(i){
if (i !== cL) counter = 0;
counter++;
cL = i;
if (counter <= amount ) finalString = finalString + i;
});
return finalString;
}
You can use reg expression instead. tested in javascript.
how it works:
(.) //match any character
\1 //if it follow by the same character
+{2 //more than 1 times
/g //global
$1 //is 1 time by $1$1 is 2 times
reduceString('aaaabbbb', 2)
reduceString('xaaabbbb', 2)
reduceString('aaaabbbb', 1)
reduceString('aaxxxaabbbb', 2)
function reduceString(txt,num)
{
var canRepeat=['$1'];
for (i=1;i<num;i++)
{
canRepeat.push('$1')
}
canRepeat = canRepeat.join('');
console.log(txt.replace(/(.)\1{2,}/g, canRepeat))
}
With regex:
var reduceString = function(str, amount) {
var x = [ ...new Set(str) ];
for (var c of x){
var rex = new RegExp(c + '{'+amount+',}','g');
str = str.replace(rex,string(c,amount));
}
return str;
};
var string = function(c,amount){
for(var i=0,s="";i<amount;i++)s+=c;
return s;
};
Up above regex solutions are much more better, but here is my accepted solution with reduce:
make an array from string via spread operator
Check the previous item
find how many times char is repeated in result string
otherwise concat result string with the current char
Don`t forget to use the second argument as the initial value, and return for each cases
reduceString = function(str, amount) {
return [...str].reduce(((res, cur)=>{
if(res.length && cur === res[res.length-1]){
dupsCount = [...res].filter(char => char === cur).length
if(dupsCount===amount){
return res;
}
else {
res+=cur;
return res;
}
}
res+=cur;
return res;
}),"")
}