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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 a string called e3 which holds the string 1,2,4,5,3,6. I want to add up all of those numbers up to make the number 21 I was considering doing a for loop for this however I do not know how to turn part of a string into its own value.
I anyone has any better idea of what to do please comment, or answer.
You could use String#split for the string and use Array#reduce for summing.
var e3 = '1,2,4,5,3,6',
sum = e3.split(',').reduce(function (a, b) {
return a + +b; // +b forces b to number
}, 0);
console.log(sum);
If you are sure that it is always a comma separated list of numbers, you could split it on the comma into an array and then use array.reduce() to sum them
var asString = '1,2,4,5,3,6';
var asArray = asString.split(',');
var total = asArray.reduce(function(prev, current){
return prev + parseInt(current, 10);
}, 0);
console.log(total) // outputs 21;
You can do it like this:
var e3 = "1,2,4,5,3,6";
// Split by separator ','
var stringsArr = e3.split(',');
var sum = 0;
// Loop through array of string numbers
stringsArr.forEach(function(str) {
// get Int from a string
var strVal = parseInt(str, 10);
sum += strVal;
});
here's the fiddle
Here is working code to do what you need: https://plnkr.co/edit/8LSkZi0oC8msbHI0qOrz?p=preview
At first you use the split method - this separates a string into an array of strings, based on some separator value. In our case, the separator is a comma, but it could be a blank space or something else:
var testString = '1,2,4,5,3,6';
var separator = ',';
function splitStringOnCommasAndGetArray(string, separator){
var arrayOfStrings = string.split(separator);
return arrayOfStrings;
}
After that, we loop through the array and turn each value into a number. We add the numbers, like so:
function addUpArray(arrayOfStrings){
var totalNumber = 0;
for(var i = 0; i < arrayOfStrings.length; i++){
var currentNum = parseInt(arrayOfStrings[i]);
console.log(currentNum);
totalNumber += currentNum;
}
return totalNumber;
}
I am stuck a bit with replacing string in js array. I am trying to log the arguments to see what is going on but am missing a piece of the puzzle.
fiddle
// - trying to look for substring in array
// - if match is found
// - replace substring without using the native method replace();
var div = $('.insert');
data = ["erf,", "erfeer,rf", "erfer"];
data = data.map(function (x) {
return /""/g.test(x) ? x.replace(/""/g, "") : x
});
function fakeReplace(data, substr, newstr) {
//should show ["erf,", "erfeer,rf", "erfer"];
div.append("data before match replace = " + data);
div.append("\<br>");
div.append("substr = " + substr);
div.append("\<br>");
div.append("newstr = " + newstr);
div.append("\<br>");
return data.split(substr).join(newstr);
}
fakeReplace(data, "erf", "blue");
//should show ["blue,", "blueeer,rf", "blueer"];
div.append("data after fakeReplace is executed = " + data);
You are treating data like a string in your function. You can use map() to return a new array with each element replaced.
function fakeReplace(data, substr, newstr) {
return data.map(function(s) {
return s.split(substr).join(newstr);
})
}
let myString = "Victor";
let splitted = myString.split('');
function replaceManual(a,b){
for(let i = 0; i<= splitted.length-1; i++)
{
for(let j=i; j <=i;j++)
{
if(splitted[j]===a)
{
splitted[j]=b;
return splitted;
}
else
{
break;
}
}
}
}
replaceManual('V','T');
console.log(splitted.toString().replace(/[^\w\s]/gi, ''));
How can I insert a string at a specific index of another string?
var txt1 = "foo baz"
Suppose I want to insert "bar " after the "foo" how can I achieve that?
I thought of substring(), but there must be a simpler more straight forward way.
Inserting at a specific index (rather than, say, at the first space character) has to use string slicing/substring:
var txt2 = txt1.slice(0, 3) + "bar" + txt1.slice(3);
You could prototype your own splice() into String.
Polyfill
if (!String.prototype.splice) {
/**
* {JSDoc}
*
* The splice() method changes the content of a string by removing a range of
* characters and/or adding new characters.
*
* #this {String}
* #param {number} start Index at which to start changing the string.
* #param {number} delCount An integer indicating the number of old chars to remove.
* #param {string} newSubStr The String that is spliced in.
* #return {string} A new string with the spliced substring.
*/
String.prototype.splice = function(start, delCount, newSubStr) {
return this.slice(0, start) + newSubStr + this.slice(start + Math.abs(delCount));
};
}
Example
String.prototype.splice = function(idx, rem, str) {
return this.slice(0, idx) + str + this.slice(idx + Math.abs(rem));
};
var result = "foo baz".splice(4, 0, "bar ");
document.body.innerHTML = result; // "foo bar baz"
EDIT: Modified it to ensure that rem is an absolute value.
Here is a method I wrote that behaves like all other programming languages:
String.prototype.insert = function(index, string) {
if (index > 0)
{
return this.substring(0, index) + string + this.substring(index, this.length);
}
return string + this;
};
//Example of use:
var something = "How you?";
something = something.insert(3, " are");
console.log(something)
Reference:
http://coderamblings.wordpress.com/2012/07/09/insert-a-string-at-a-specific-index/
Just make the following function:
function insert(str, index, value) {
return str.substr(0, index) + value + str.substr(index);
}
and then use it like that:
alert(insert("foo baz", 4, "bar "));
Output: foo bar baz
It behaves exactly, like the C# (Sharp) String.Insert(int startIndex, string value).
NOTE: This insert function inserts the string value (third parameter) before the specified integer index (second parameter) in the string str (first parameter), and then returns the new string without changing str!
UPDATE 2016: Here is another just-for-fun (but more serious!) prototype function based on one-liner RegExp approach (with prepend support on undefined or negative index):
/**
* Insert `what` to string at position `index`.
*/
String.prototype.insert = function(what, index) {
return index > 0
? this.replace(new RegExp('.{' + index + '}'), '$&' + what)
: what + this;
};
console.log( 'foo baz'.insert('bar ', 4) ); // "foo bar baz"
console.log( 'foo baz'.insert('bar ') ); // "bar foo baz"
Previous (back to 2012) just-for-fun solution:
var index = 4,
what = 'bar ';
'foo baz'.replace(/./g, function(v, i) {
return i === index - 1 ? v + what : v;
}); // "foo bar baz"
This is basically doing what #Base33 is doing except I'm also giving the option of using a negative index to count from the end. Kind of like the substr method allows.
// use a negative index to insert relative to the end of the string.
String.prototype.insert = function (index, string) {
var ind = index < 0 ? this.length + index : index;
return this.substring(0, ind) + string + this.substr(ind);
};
Example:
Let's say you have full size images using a naming convention but can't update the data to also provide thumbnail urls.
var url = '/images/myimage.jpg';
var thumb = url.insert(-4, '_thm');
// result: '/images/myimage_thm.jpg'
If anyone is looking for a way to insert text at multiple indices in a string, try this out:
String.prototype.insertTextAtIndices = function(text) {
return this.replace(/./g, function(character, index) {
return text[index] ? text[index] + character : character;
});
};
For example, you can use this to insert <span> tags at certain offsets in a string:
var text = {
6: "<span>",
11: "</span>"
};
"Hello world!".insertTextAtIndices(text); // returns "Hello <span>world</span>!"
Instantiate an array from the string
Use Array#splice
Stringify again using Array#join
The benefits of this approach are two-fold:
Simple
Unicode code point compliant
const pair = Array.from('USDGBP')
pair.splice(3, 0, '/')
console.log(pair.join(''))
Given your current example you could achieve the result by either
var txt2 = txt1.split(' ').join(' bar ')
or
var txt2 = txt1.replace(' ', ' bar ');
but given that you can make such assumptions, you might as well skip directly to Gullen's example.
In a situation where you really can't make any assumptions other than character index-based, then I really would go for a substring solution.
my_string = "hello world";
my_insert = " dear";
my_insert_location = 5;
my_string = my_string.split('');
my_string.splice( my_insert_location , 0, my_insert );
my_string = my_string.join('');
https://jsfiddle.net/gaby_de_wilde/wz69nw9k/
I know this is an old thread, however, here is a really effective approach.
var tn = document.createTextNode("I am just to help")
t.insertData(10, "trying");
What's great about this is that it coerces the node content. So if this node were already on the DOM, you wouldn't need to use any query selectors or update the innerText. The changes would reflect due to its binding.
Were you to need a string, simply access the node's text content property.
tn.textContent
#=> "I am just trying to help"
You can do it easily with regexp in one line of code
const str = 'Hello RegExp!';
const index = 6;
const insert = 'Lovely ';
//'Hello RegExp!'.replace(/^(.{6})(.)/, `$1Lovely $2`);
const res = str.replace(new RegExp(`^(.{${index}})(.)`), `$1${insert}$2`);
console.log(res);
"Hello Lovely RegExp!"
Well, we can use both the substring and slice method.
String.prototype.customSplice = function (index, absIndex, string) {
return this.slice(0, index) + string+ this.slice(index + Math.abs(absIndex));
};
String.prototype.replaceString = function (index, string) {
if (index > 0)
return this.substring(0, index) + string + this.substr(index);
return string + this;
};
console.log('Hello Developers'.customSplice(6,0,'Stack ')) // Hello Stack Developers
console.log('Hello Developers'.replaceString(6,'Stack ')) //// Hello Stack Developers
The only problem of a substring method is that it won't work with a negative index. It's always take string index from 0th position.
You can use Regular Expressions with a dynamic pattern.
var text = "something";
var output = " ";
var pattern = new RegExp("^\\s{"+text.length+"}");
var output.replace(pattern,text);
outputs:
"something "
This replaces text.length of whitespace characters at the beginning of the string output.
The RegExp means ^\ - beginning of a line \s any white space character, repeated {n} times, in this case text.length. Use \\ to \ escape backslashes when building this kind of patterns out of strings.
another solution, cut the string in 2 and put a string in between.
var str = jQuery('#selector').text();
var strlength = str.length;
strf = str.substr(0 , strlength - 5);
strb = str.substr(strlength - 5 , 5);
jQuery('#selector').html(strf + 'inserted' + strb);
Using slice
You can use slice(0,index) + str + slice(index). Or you can create a method for it.
String.prototype.insertAt = function(index,str){
return this.slice(0,index) + str + this.slice(index)
}
console.log("foo bar".insertAt(4,'baz ')) //foo baz bar
Splice method for Strings
You can split() the main string and add then use normal splice()
String.prototype.splice = function(index,del,...newStrs){
let str = this.split('');
str.splice(index,del,newStrs.join('') || '');
return str.join('');
}
var txt1 = "foo baz"
//inserting single string.
console.log(txt1.splice(4,0,"bar ")); //foo bar baz
//inserting multiple strings
console.log(txt1.splice(4,0,"bar ","bar2 ")); //foo bar bar2 baz
//removing letters
console.log(txt1.splice(1,2)) //f baz
//remving and inseting atm
console.log(txt1.splice(1,2," bar")) //f bar baz
Applying splice() at multiple indexes
The method takes an array of arrays each element of array representing a single splice().
String.prototype.splice = function(index,del,...newStrs){
let str = this.split('');
str.splice(index,del,newStrs.join('') || '');
return str.join('');
}
String.prototype.mulSplice = function(arr){
str = this
let dif = 0;
arr.forEach(x => {
x[2] === x[2] || [];
x[1] === x[1] || 0;
str = str.splice(x[0] + dif,x[1],...x[2]);
dif += x[2].join('').length - x[1];
})
return str;
}
let txt = "foo bar baz"
//Replacing the 'foo' and 'bar' with 'something1' ,'another'
console.log(txt.splice(0,3,'something'))
console.log(txt.mulSplice(
[
[0,3,["something1"]],
[4,3,["another"]]
]
))
I wanted to compare the method using substring and the method using slice from Base33 and user113716 respectively, to do that I wrote some code
also have a look at this performance comparison, substring, slice
The code I used creates huge strings and inserts the string "bar " multiple times into the huge string
if (!String.prototype.splice) {
/**
* {JSDoc}
*
* The splice() method changes the content of a string by removing a range of
* characters and/or adding new characters.
*
* #this {String}
* #param {number} start Index at which to start changing the string.
* #param {number} delCount An integer indicating the number of old chars to remove.
* #param {string} newSubStr The String that is spliced in.
* #return {string} A new string with the spliced substring.
*/
String.prototype.splice = function (start, delCount, newSubStr) {
return this.slice(0, start) + newSubStr + this.slice(start + Math.abs(delCount));
};
}
String.prototype.splice = function (idx, rem, str) {
return this.slice(0, idx) + str + this.slice(idx + Math.abs(rem));
};
String.prototype.insert = function (index, string) {
if (index > 0)
return this.substring(0, index) + string + this.substring(index, this.length);
return string + this;
};
function createString(size) {
var s = ""
for (var i = 0; i < size; i++) {
s += "Some String "
}
return s
}
function testSubStringPerformance(str, times) {
for (var i = 0; i < times; i++)
str.insert(4, "bar ")
}
function testSpliceStringPerformance(str, times) {
for (var i = 0; i < times; i++)
str.splice(4, 0, "bar ")
}
function doTests(repeatMax, sSizeMax) {
n = 1000
sSize = 1000
for (var i = 1; i <= repeatMax; i++) {
var repeatTimes = n * (10 * i)
for (var j = 1; j <= sSizeMax; j++) {
var actualStringSize = sSize * (10 * j)
var s1 = createString(actualStringSize)
var s2 = createString(actualStringSize)
var start = performance.now()
testSubStringPerformance(s1, repeatTimes)
var end = performance.now()
var subStrPerf = end - start
start = performance.now()
testSpliceStringPerformance(s2, repeatTimes)
end = performance.now()
var splicePerf = end - start
console.log(
"string size =", "Some String ".length * actualStringSize, "\n",
"repeat count = ", repeatTimes, "\n",
"splice performance = ", splicePerf, "\n",
"substring performance = ", subStrPerf, "\n",
"difference = ", splicePerf - subStrPerf // + = splice is faster, - = subStr is faster
)
}
}
}
doTests(1, 100)
The general difference in performance is marginal at best and both methods work just fine (even on strings of length ~~ 12000000)
Take the solution. I have written this code in an easy format:
const insertWord = (sentence,word,index) => {
var sliceWord = word.slice(""),output = [],join; // Slicing the input word and declaring other variables
var sliceSentence = sentence.slice(""); // Slicing the input sentence into each alphabets
for (var i = 0; i < sliceSentence.length; i++)
{
if (i === index)
{ // checking if index of array === input index
for (var j = 0; j < word.length; j++)
{ // if yes we'll insert the word
output.push(sliceWord[j]); // Condition is true we are inserting the word
}
output.push(" "); // providing a single space at the end of the word
}
output.push(sliceSentence[i]); // pushing the remaining elements present in an array
}
join = output.join(""); // converting an array to string
console.log(join)
return join;
}
Prototype should be the best approach as many mentioned. Make sure that prototype comes earlier than where it is used.
String.prototype.insert = function (x, str) {
return (x > 0) ? this.substring(0, x) + str + this.substr(x) : str + this;
};
the list looks like:
3434,346,1,6,46
How can I append a number to it with javascript, but only if it doesn't already exist in it?
Assuming your initial value is a string (you didn't say).
var listOfNumbers = '3434,346,1,6,46', add = 34332;
var numbers = listOfNumbers.split(',');
if(numbers.indexOf(add)!=-1) {
numbers.push(add);
}
listOfNumbers = numbers.join(',');
Basically i convert the string into an array, check the existence of the value using indexOf(), adding only if it doesn't exist.
I then convert the value back to a string using join.
If that is a string, you can use the .split() and .join() functions, as well as .push():
var data = '3434,346,1,6,46';
var arr = data.split(',');
var add = newInt;
arr.push(newInt);
data = arr.join(',');
If that is already an array, you can just use .push():
var data = [3434,346,1,6,46];
var add = newInt;
data.push(add);
UPDATE: Didn't read the last line to check for duplicates, the best approach I can think of is a loop:
var data = [3434,346,1,6,46];
var add = newInt;
var exists = false;
for (var i = 0; i < input.length; i++) {
if (data[i] == add) {
exists = true;
break;
}
}
if (!exists) {
data.push(add);
// then you would join if you wanted a string
}
You can also use a regular expression:
function appendConditional(s, n) {
var re = new RegExp('(^|\\b)' + n + '(\\b|$)');
if (!re.test(s)) {
return s + (s.length? ',' : '') + n;
}
return s;
}
var nums = '3434,346,1,6,46'
alert( appendConditional(nums, '12') ); // '3434,346,1,6,46,12'
alert( appendConditional(nums, '6') ); // '3434,346,1,6,46'
Oh, since some really like ternary operators and obfustically short code:
function appendConditional(s, n) {
var re = new RegExp('(^|\\b)' + n + '(\\b|$)');
return s + (re.test(s)? '' : (''+s? ',':'') + n );
}
No jQuery, "shims" or cross-browser issues. :-)