The Question
If I want to use slice to get the last character of a string I would do..
lastCharacter = theString.slice(-1);
Is it possible to select the last character with both a start and end numerical parameter? Like this..
var start = -1;
var end = -0; // nonsensical, I realize
lastCharacter = theString.slice(start, end);
The Answer
There's no special -0 digit
The Reason I Asked
The reason I asked is I was looking to use variables for both parameters which would decrement on each loop as I built a new variable which would be the reverse of theString. Until atomrc's answer I didn't think to simply use theString.length and work back from the last character rather than using -1 to start with the last character as I do in the example below (which requires an if statement for the first iteration of the for loop).
It was for the third question on codeschools arcade javascript test 'Check if string is a palindrome'
My solution was..
function checkPalindrome(inputString) {
var characterTotal = inputString.length;
var inputStringStringified = inputString + '';
var slicedLetter;
var sliceStart = -1;
var sliceEnd = -1;
var backwards = '';
for (i = characterTotal; i > 0; i--) {
if (i === characterTotal) { // first run
slicedLetter = inputStringStringified.slice(sliceStart);
sliceStart = sliceStart - 1;
backwards = backwards + slicedLetter;
} else {
slicedLetter = inputStringStringified.slice(sliceStart, sliceEnd);
sliceStart = sliceStart - 1;
sliceEnd = sliceEnd - 1;
backwards = backwards + slicedLetter;
}
}
if (inputString === backwards) {
alert('true');
} else {
alert('false');
}
}
checkPalindrome('abaaba');
I had to create an if statement for the first iteration. With atomrc's answer I see now I didn't have to use negative numbers for slice as I knew the strings length.
With new knowledge my new solution is a bit shorter..
function checkPalindrome(theString) {
var totalCharacters = theString.length;
var sliceStart = totalCharacters - 1;
var sliceEnd = totalCharacters;
var counter = totalCharacters;
var backwardsString = '';
while (counter > 0) {
var character = theString.slice(sliceStart, sliceEnd);
sliceStart--;
sliceEnd--;
counter--;
backwardsString = backwardsString + character;
}
if (theString === backwardsString) {
alert('its a palindrome');
} else {
alert('its not a palindrome');
}
}
checkPalindrome('abaaba');
..but still a terrible solution. After solving it I saw what others came up with and some are simple one liners.
There you go :)
theString.slice(theString.length - 1, theString.length)
how do I count the frequency of the elements in the array, I'm new to Javascript and completely lost, I have looked at other answers here but can't get them to work for me. Any help is much appreciated.
function getText() {
var userText;
userText = document.InputForm.MyTextBox.value; //get text as string
alphaOnly(userText);
}
function alphaOnly(userText) {
var nuText = userText;
//result = nuText.split("");
var alphaCheck = /[a-zA-Z]/g; //using RegExp create variable to have only alphabetic characters
var alphaResult = nuText.match(alphaCheck); //get object with only alphabetic matches from original string
alphaResult.sort();
var result = freqLet(alphaResult);
document.write(countlist);
}
function freqLet(alphaResult) {
count = 0;
countlist = {
alphaResult: count
};
for (i = 0; i < alphaResult.length; i++) {
if (alphaResult[i] in alphaResult)
count[i] ++;
}
return countlist;
}
To count frequencies you should use an object which properties correspond to the letters occurring in your input string.
Also before incrementing the value of the property you should previously check whether this property exists or not.
function freqLet (alphaResult) {
var count = {};
countlist = {alphaResult:count};
for (i = 0; i < alphaResult.length; i++) {
var character = alphaResult.charAt(i);
if (count[character]) {
count[character]++;
} else {
count[character] = 1;
}
}
return countlist;
}
If you can use a third party library, underscore.js provides a function "countBy" that does pretty much exactly what you want.
_.countBy(userText, function(character) {
return character;
});
This should return an associative array of characters in the collection mapped to a count.
Then you could filter the keys of that object to the limited character set you need, again, using underscore or whatever method you like.
Do as below:
var __arr = [6,7,1,2,3,3,4,5,5,5]
function __freq(__arr){
var a = [], b = [], prev
__arr.sort((a,b)=>{return a- b} )
for(let i = 0; i<__arr.length; i++){
if(__arr[i] !== prev){
a.push(__arr[i])
b.push(1)
}else{
b[b.length - 1]++
}
prev = __arr[i]
}
return [a , b]
}
I need to replace all the specials characters in a string with javascript or jQuery.
I am sure there is a better way to do this.
But I currently have no clue.
Anyone got an idea?
function Unaccent(str) {
var norm = new Array('À','Á','Â','Ã','Ä','Å','Æ','Ç','È','É','Ê','Ë','Ì','Í','Î','Ï', 'Ð','Ñ','Ò','Ó','Ô','Õ','Ö','Ø','Ù','Ú','Û','Ü','Ý','Þ','ß', 'à','á','â','ã','ä','å','æ','ç','è','é','ê','ë','ì','í','î','ï','ð','ñ', 'ò','ó','ô','õ','ö','ø','ù','ú','û','ü','ý','ý','þ','ÿ');
var spec = new Array('A','A','A','A','A','A','A','C','E','E','E','E','I','I','I','I', 'D','N','O','O','O','0','O','O','U','U','U','U','Y','b','s', 'a','a','a','a','a','a','a','c','e','e','e','e','i','i','i','i','d','n', 'o','o','o','o','o','o','u','u','u','u','y','y','b','y');
for (var i = 0; i < spec.length; i++) {
str = replaceAll(str, norm[i], spec[i]);
}
return str;
}
function replaceAll(str, search, repl) {
while (str.indexOf(search) != -1) {
str = str.replace(search, repl);
}
return str;
}
Here's a version using a lookup map that works a little more efficiently than nested loops:
function Unaccent(str) {
var map = Unaccent.map; // shortcut
var result = "", srcChar, replaceChar;
for (var i = 0, len = str.length; i < len; i++) {
srcChar = str.charAt(i);
// use hasOwnProperty so we never conflict with any
// methods/properties added to the Object prototype
if (map.hasOwnProperty(srcChar)) {
replaceChar = map[srcChar]
} else {
replaceChar = srcChar;
}
result += replaceChar;
}
return(result);
}
// assign this here so it is only created once
Unaccent.map = {'À':'A','Á':'A','Â':'A'}; // you fill in the rest of the map
Working demo: http://jsfiddle.net/jfriend00/rRpcy/
FYI, a Google search for "accent folding" returns many other implementations (many similar, but also some using regex).
Here's a bit higher performance version (2.5x faster) that can do a direct indexed lookup of the accented characters rather than having to do an object lookup:
function Unaccent(str) {
var result = "", code, lookup, replaceChar;
for (var i = 0, len = str.length; i < len; i++) {
replaceChar = str.charAt(i);
code = str.charCodeAt(i);
// see if code is in our map
if (code >= 192 && code <= 255) {
lookup = Unaccent.map.charAt(code - 192);
if (lookup !== ' ') {
replaceChar = lookup;
}
}
result += replaceChar;
}
return(result);
}
// covers chars from 192-255
// blank means no mapping for that char
Unaccent.map = "AAAAAAACEEEEIIIIDNOOOOO OUUUUY aaaaaaaceeeeiiiionooooo uuuuy y";
Working demo: http://jsfiddle.net/jfriend00/Jxr9u/
In this jsperf, the string lookup version (the 2nd example) is about 2.5x faster.
Using an object as a map is a good idea, but given the number of characters you're replacing, it's probably a good idea to pre-initialize the object so that it doesn't have to be re-initialized each time the function gets run (assuming you're running the function more than once):
var Unaccent = (function () {
var charMap = {'À':'A','Á':'A','Â':'A','Ã':'A','Ä':'A' /** etc. **/};
return function (str) {
var i, modified = "", cur;
for(i = 0; i < str.length; i++) {
cur = str.charAt(i);
modified += (charMap[cur] || cur);
}
return modified;
};
}());
This will front-load the heavy lifting of the function to page load time (you can do some modifications to delay it until the first call to the function if you like). But it will take some of the processing time out of the actual function call.
It's possible some browsers will actually optimize this part anyway, so you might not see a benefit. But on older browsers (where performance is of greater concern), you'll probably see some benefit to pre-processing your character map.
You can prepare key value pair type of array and via jquery each traverse that array.
Example :
function Unaccent(str) {
var replaceString = {'À':'A','Á':'A','Â':'A'}; // add more
$.each(replaceString, function(k, v) {
var regX = new RegExp(k, 'g');
str = str.replace(regX,v);
});
}
Working Demo
Good Luck !!
I am trying to grab a certain value. I am new to javascript and I can't figure out why this is not working.
If I parse "kid_2" I should get "kostas". Instead of "Kostas" I always get "02-23-2000". So I must have a logic problem in the loop but I am really stuck.
function getold_val(fieldname,str){
var chunks=str.split("||");
var allchunks = chunks.length-1;
for(k=0;k<allchunks;k++){
var n=str.indexOf(fieldname);
alert(chunks[k]);
if(n>0){
var chunkd=chunks[k].split("::");
alert(chunkd);
return chunkd[1];
}
}
}
var test = getold_val('kid_2','date_1::02-23-2000||date_2::06-06-1990||kid_1::George||kid_2::Kostas||');
alert(test);
A regex may be a little more appealing. Here's a fiddle:
function getValue(source, key){
return (new RegExp("(^|\\|)" + key + "::([^$\\|]+)", "i").exec(source) || {})[2];
}
getValue("date_1::02-23-2000||date_2::06-06-1990||kid_1::George||kid_2::Kostas||","kid_2");
But if you want something a little more involved, you can parse that string into a dictionary like so (fiddle):
function splitToDictionary(val, fieldDelimiter, valueDelimiter){
var dict = {},
fields = val.split(fieldDelimiter),
kvp;
for (var i = 0; i < fields.length; i++) {
if (fields[i] !== "") {
kvp = fields[i].split(valueDelimiter);
dict[kvp[0]] = kvp[1];
}
}
return dict;
}
var dict = splitToDictionary("date_1::02-23-2000||date_2::06-06-1990||kid_1::George||kid_2::Kostas||","||","::");
console.log(dict["date_1"]);
console.log(dict["date_2"]);
console.log(dict["kid_1"]);
console.log(dict["kid_2"]);
This works, here's my fiddle.
function getold_val(fieldname,str) {
var chunks = str.split('||');
for(var i = 0; i < chunks.length-1; i++) {
if(chunks[i].indexOf(fieldname) >= 0) {
return(chunks[i].substring(fieldname.length+2));
}
}
}
alert(getold_val('kid_2', 'date_1::02-23-2000||date_2::06-06-1990||kid_1::George||kid_2::Kostas||'));
The issue with your code was (as #slebetman noticed as well) the fact that a string index can be 0 because it starts exactly in the first letter.
The code is almost the same as yours, I just didn't use the second .split('::') because I felt a .substring(...) would be easier.
There are two bugs. The first error is in the indexOf call:
var n = str.indexOf(fieldname);
This will always return a value greater than or equal to 0 since the field exists in the string. What you should be doing is:
var n = chunks[k].indexOf(fieldname);
The second error is in your if statement. It should be:
if(n >= 0) {
...
}
or
if(n > -1) {
...
}
The substring you are looking for could very well be the at the beginning of the string, in which case its index is 0. indexOf returns -1 if it cannot find what you're looking for.
That being said, here's a better way to do what you're trying to do:
function getold_val(fieldName, str) {
var keyValuePairs = str.split("||");
var returnValue = null;
if(/||$/.match(str)) {
keyValuePairs = keyValuePairs.slice(0, keyValuePairs.length - 1);
}
var found = false;
var i = 0;
while(i < keyValuePairs.length && !found) {
var keyValuePair = keyValuePairs[i].split("::");
var key = keyValuePair[0];
var value = keyValuePair[1];
if(fieldName === key) {
returnValue = value;
found = true;
}
i++;
}
return returnValue;
}
I have a problem with this script, something is going wrong.
Rnumer stays undefined.This script should return and write all uneven digits from the random number list. Can someone tell me what I do wrong. Thanks in advance
var Rnumber = new Array();
for (i = 0; i<= 100;i++)
{
Rnumber[i] = Math.ceil(Math.random()*101);
// document.write(Rnumber[i] + "<br/>");
}
function unevenAndDivisible(Rnumber)
{
var remainder = new Array();
for (i = 0; i<= 100; i++)
{
remainder = parseInt(Rnumber[i])%2;
}
return remainder;
}
document.write(unevenAndDivisible());
Changed to
var Rnumber = new Array();
for (i = 0; i<= 100;i++)
{
Rnumber[i] = Math.ceil(Math.random()*101);
// document.write(Rnumber[i] + "<br/>");
}
function unevenAndDivisible(Rnumber)
{
var remainder = new Array();
for (i = 0; i<= 100; i++)
{
remainder[i] = Rnumber[i]%2;
}
return remainder;
}
document.write(unevenAndDivisible(Rnumber));
but now i get the result :
0,1,0,0,1,0,0,0,1,1,0,0,1,0,1,1,1....
I simply want maybe I asked it wrong the first time, to write al uneven numbers from the random list of Rnumbers
Then I need to divide that through 7 and return that.
EDIT
Allmost all problems are clear , thanks everyone for that.
Their is still one question left:
In this code below it only take the first uneven value from remainder and I want that it takes all values that are uneven to the next if statement to check %7.
Maybe you see the problem better if you run it for youreself
var Rnumber = new Array();
for (i = 0; i<= 100;i++)
{
Rnumber[i] = Math.ceil(Math.random()*101);
}
function unevenAndDivisible()
{
var remainder = [];
var answer = [];
for (i = 0; i<= 100; i++)
{
if (Rnumber[i]%2 !== 0)
{
remainder.push(Rnumber[i]);
for (c = 0; c <= remainder.length;c++)
{
if (remainder[c]%7 == 0)
{
answer.push(remainder[c]);
}
}
}
}
return answer;
}
answer = unevenAndDivisible();
document.write(answer);
Problem solved , Thanks everyone
You don't need to pass Rnumber to the function, as it's already available in scope:
function unevenAndDivisible()
{
var remainder = [];
for (i = 0; i<= 100; i++)
{
if (Rnumber[i]%2 !== 0) {
remainder.push(Rnumber[i]);
}
}
return remainder;
}
remainder = unevenAndDivisible();
console.log(remainder);
JS Fiddle demo.
Edited in response to question from OP (in comments to question, above):
...can someone explain what this mean: var remainder = [];
Sure, it's array-literal notation, which is equal to: var remainder = new Array();, it's just a little more concise, and I prefer to save myself the typing. I get the impression, from JS Lint, whenever I use var x = new Array(); therein that the above version is generally preferred (since it complains otherwise), but I don't know why.
Either pass Rnumber to the function unevenAndDivisible or omit it from the argument list. Since it is an argument, it has more local scope than the initial declaration of Rnumber.
Your problem is the line
function unevenAndDivisible(Rnumber)
You are passing in Rnumber in as an argument, but when you call unevenAndDivisible()
you are not passing it it.
Consequently for the body of the function Rnumber is undefined (cause you passed nothing in)
The following snippet is equivalent to what you wrote nad might explain better
function unevenAndDivisible(xyz)
{
var remainder = new Array();
for (i = 0; i<= 100; i++)
{
remainder = parseInt(xyz[i])%2;
}
return remainder;
}
then called as
unevenAndDivisible(undefined)
to fix it remove the argument from the call definition
i.e. define it as
function unevenAndDivisible()
1 - you is not defining the Rnumber value that's function argument.
2 - in loop, you're defining remainder to divised value of ranumber and is not saving in array; try:
change:
remainder = parseInt(Rnumber[i])%2;
to
remainder[i] = parseInt(Rnumber[i])%2;
var array = [],
i = 100;
while (i--) {
var random = Math.random()*i|0;
if(random % 2)
array.unshift(random);
}
alert(array);