I am following a tutorial about nodejs. In the tutorial it has this example:
const fs = require('fs');
const conversionMap = {
'88': '65',
'89': '66',
'90': '67',
};
fs.readFile(__filename, (err, buffer) => {
let tag = buffer.slice(-4, -1);
for(let i=0;i < tag.length; i++) {
tag[i] = conversionMap[tag[i]];
}
console.log(buffer.toString());
});
// TAG: XYZ
I am pretty sure I know what this example is doing. It is reading the file, then allocating it to a buffer and writing it out. I know that it finds the TAG via slice(-4, -1) (The tag it 1 up from the bottom and for over). I am just not sure it changes it.
Thanks in advance for the help!
Yes it changes each time because it is running a loop and iterating the value of i.
tag will give you the buffer.sliced value and tag.length will have that number.
So the i value will have an initialization with 0 and then it will run the loop till it reaches the tag.length
So if buffer.slice(-4, -1) results in "text", then the loop will consider tag.length as 4 and the i will consider upto 3 (i < tag.length).
So, conversionMap is a map which does the Key= value mapping.
In this case , 88 is the key and the corresponding value is 65 for it.
But , it is doing the conversion for the character's decimal value(which is i ).
You can check that in the ASCII table for your reference.
Related
I'm currently making a program with many functions that utilise Math.rand(). I'm trying to generate a string with a given keyword (in this case, lathe). I want the program to log a string that has "lathe" (or any version of it, with capitals or not), but everything I've tried has the program hit its call stack size limit (I understand exactly why, I want the program to generate a string with the word without it hitting its call stack size).
What I have tried:
function generateStringWithKeyword(randNum: number) {
const chars = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789+/";
let result = "";
for(let i = 0; i < randNum; i++) {
result += chars[Math.floor(Math.random() * chars.length)];
if(result.includes("lathe")) {
continue;
} else {
generateStringWithKeyword(randNum);
}
}
console.log(result);
}
This is what I have now, after doing brief research on stackoverflow I learned that it might have been better to add the if/else block with a continue, rather than using
if(!result.includes("lathe")) return generateStringWithKeyword(randNum);
But both ways I had hit the call stack size limit.
A "correct" version of your algorithm, written as an iterative function instead of as a recursive one so as not to exceed stack depth, would look something like this:
function generateStringWithKeyword(randNum: number) {
const chars = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789+/";
let result = "";
let attemptCnt = 0;
while (!result.toLowerCase().includes("lathe")) {
attemptCnt++;
result = "";
for (let i = 0; i < randNum; i++) {
result += chars[Math.floor(Math.random() * chars.length)];
}
if (attemptCnt > 1e6) {
console.log("I GIVE UP");
return;
}
}
console.log(result);
return result;
}
I don't like when my browser hangs because of a script that won't finish, so I put a maximum attempt count in there. A million chances seems reasonable. When you try it out, this happens:
generateStringWithKeyword(10); // I GIVE UP
Which makes sense; let's perform a rough back-of-the-envelope probability calculation to see how long we might expect this to take. The chance that "lathe" will appear in some case at position 1 of the word is (2/64)×(2/64)×(2×64)×(2/64)×(2/64) ("L" or "l" appears first, followed by "A" or "a", etc) which is approximately 3×10-8. For a word of length 10, "lathe" can appear starting at positions 1, 2, 3, 4, 5, or 6. While this isn't exactly correct, let's think of this as multiplying your chances by 6 of getting the word somewhere, so the actual chance of getting a valid result is somewhere around 1.8×10-7. So we can expect that you'd need to make approximately 1 ÷ 1.8×10-7 = 5.6 million chances to succeed.
Oh, darn, I only gave it a million. Let's up that to 10 million and try again:
generateStringWithKeyword(10); // "lATHELEYSc"
Great! Although, it does sometimes still give up. And really, an algorithm which needs millions of tries before it succeeds is very, very inefficient. You might want to read about bogosort, a sorting algorithm which works by randomly shuffling things and checking to see if they are sorted, and it keeps trying until it works. It's used for educational purposes to highlight how such techniques don't really perform well enough to be practical. Nobody would ever want to use such an algorithm for real.
So how would you do this "the right" way? Well, my suggestion here is to just build your result correctly the first time. If you have 10 characters and 5 of them need to be "lathe" in some case, then you will need 5 truly random characters. So randomly decide how many of those letters should be before "lathe". If you pick 2, for example, then put 2 random characters, plus "lathe" in a random case, plus 3 more random characters.
It could be something like this, where I mostly use your same style of for-loops and += string concatenation:
function generateStringWithKeyword(randNum: number) {
const keyword = "lathe";
if (randNum < keyword.length) throw new Error(
"This is not possible; \"" + keyword + "\" doesn't fit in " + randNum + " characters"
);
const actuallyRandNum = randNum - keyword.length;
const chars = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789+/";
let result = "";
const kwInsertionPoint = Math.floor(Math.random() * (actuallyRandNum + 1));
for (let i = 0; i < kwInsertionPoint; i++) {
result += chars[Math.floor(Math.random() * chars.length)];
}
for (let i = 0; i < keyword.length; i++) {
result += Math.random() < 0.5 ? keyword[i].toLowerCase() : keyword[i].toUpperCase();
}
for (let i = kwInsertionPoint; i < actuallyRandNum; i++) {
result += chars[Math.floor(Math.random() * chars.length)];
}
return result;
}
If you run this, you will see that it is very efficient, and never gives up:
console.log(Array.from({ length: 4 }, () => generateStringWithKeyword(5)).join(" "));
// "lathE LaThe lATHe LatHe"
console.log(Array.from({ length: 4 }, () => generateStringWithKeyword(7)).join(" "));
// "p6lAtHe laThE01 nlaTheK lATHeRJ"
console.log(Array.from({ length: 4 }, () => generateStringWithKeyword(10)).join(" "));
// "giMqzLaTHe 5klAthegBo oVdLatHe0q twNlATheCr"
Playground link to code
Some background on what is going on:
We are processing addresses into standardized forms, this is the code to take addresses scored by how many components found and then rescore them using a levenshtein algorithm across similar post codes
The scores are how many components were found in that address divided by the number missed, to return a ratio
The input data, scoreDict, is a dictionary containing arrays of arrays. The first set of arrays is the scores, so there are 12 arrays because there are 12 scores in this file (it adjusts by file). There are then however many addresses fit that score in their own separate arrays stored in that. Don't ask me why I'm doing it that way, my brain is dead
The code correctly goes through each score array and each one is properly filled with the unique elements that make it up. It is not short by any amount, nothing is duplicated, I have checked
When we hit the score that is -1 (this goes to any address where it doesn't fit in some rule so we can't use its post code to find components so no components are found) the loop specifically ONLY DOES EVERY OTHER ADDRESS IN THIS SCORE ARRAY
It doesn't do this to any other score array, I have checked
I have tried changing the number to something else like 99, same issue except one LESS address got rescored, and the rest stayed at the original failing score of 99
I am going insane, can anyone find where in this loop something may be going wrong to cause it to only do every other line. The index counter of line and sc come through in the correct order and do not skip over. I have checked
I am sorry this is not professional, I have been at this one loop for 5 hours
Rescore: function Rescore(scoreDict) {
let tempInc = 0;
//Loop through all scores stored in scoreDict
for (var line in scoreDict) {
let addUpdate = "";
//Loop through each line stored by score
for (var sc in scoreDict[line.toString()]) {
console.log(scoreDict[line.toString()].length);
let possCodes = new Array();
const curLine = scoreDict[line.toString()][sc];
console.log(sc);
const curScore = curLine[1].split(',')[curLine[1].split(',').length-1];
switch (true) {
case curScore == -1:
let postCode = (new RegExp('([A-PR-UWYZ][A-HK-Y]?[0-9][A-Z0-9]?[ ]?[0-9][ABD-HJLNP-UW-Z]{2})', 'i')).exec(curLine[1].replace(/\\n/g, ','));
let areaCode;
//if (curLine.split(',')[curLine.split(',').length-2].includes("REFERENCE")) {
if ((postCode = (new RegExp('(([A-Z][A-Z]?[0-9][A-Z0-9]?(?=[ ]?[0-9][A-Z]{2}))|[0-9]{5})', 'i').exec(postCode))) !== null) {
for (const code in Object.keys(addProper)) {
leven.LoadWords(postCode[0], Object.keys(addProper)[code]);
if (leven.distance < 2) {
//Weight will have adjustment algorithms based on other factors
let weight = 1;
//Add all codes that are close to the same to a temp array
possCodes.push(postCode.input.replace(postCode[0], Object.keys(addProper)[code]).split(',')[0] + "(|W|)" + (leven.distance/weight));
}
}
let highScore = 0;
let candidates = new Array();
//Use the component script from cityprocess to rescore
for (var i=0;i<possCodes.length;i++) {
postValid.add([curLine[1].split(',').slice(0,curLine[1].split(',').length-2) + '(|S|)' + possCodes[i].split("(|W|)")[0]]);
if (postValid.addChunk[0].split('(|S|)')[postValid.addChunk[0].split('(|S|)').length-1] > highScore) {
candidates = new Array();
highScore = postValid.addChunk[0].split('(|S|)')[postValid.addChunk[0].split('(|S|)').length-1];
candidates.push(postValid.addChunk[0]);
} else if (postValid.addChunk[0].split('(|S|)')[postValid.addChunk[0].split('(|S|)').length-1] == highScore) {
candidates.push(postValid.addChunk[0]);
}
}
score.Rescore(curLine, sc, candidates[0]);
}
//} else if (curLine.split(',')[curLine.split(',').length-2].contains("AREA")) {
// leven.LoadWords();
//}
break;
case curScore > 0:
//console.log("That's a pretty good score mate");
break;
}
//console.log(line + ": " + scoreDict[line].length);
}
}
console.log(tempInc)
score.ScoreWrite(score.scoreDict);
}
The issue was that I was calling the loop on the array I was editing, so as each element got removed from the array (rescored and moved into a separate array) it got shorter by that element, resulting in an issue that when the first element was rescored and removed, and then we moved onto the second index which was now the third element, because everything shifted up by 1 index
I fixed it by having it simply enter an empty array for each removed element, so everything kept its index and the array kept its length, and then clear the empty values at a later time in the code
Have to pick unique random numbers from a given array of numbers. We have a list of numbers from that system has to pick unique random numbers.
Should have an option to input count, like if we give 3 system should pick 3 numbers from the given list.
Is there any available library?
const crypto = require('crypto');
const yourNumbers = [1,2,5,3,4,5,67,34,5345,6623,4234];
let selectedNumbers = [];
let i = 0;
const numbersRequired = 4;
while (i < numbersRequired){
const pos = crypto.randomBytes(4).readUInt32BE()%yourNumbers.length;
if (selectedNumbers.includes(yourNumbers[pos])) {
continue;
}
i++;
selectedNumbers.push(yourNumbers[pos]);
}
console.log(selectedNumbers)
I won't describe the code as it's self explanatory. Also handle the scenario where you cannot pick the required amount of numbers when the yourNumbers is too short. Also change the byte size if your number list is huge
const count = 8
pickedNumbers = [];
randomNumberList = [5,7,22,45,77,33,7,33,11,22,53,46,86,57,88];
for (i =0; i< count ; i++){
const randArrayIndex = Math.floor(Math.random() * randomNumberList.length);
pickedNumbers.push(randomNumberList[randArrayIndex]);
}
console.log(pickedNumbers);
It's a simple calculation. no need for an external library. You can use the random function of the Math object to generate a random number in js. It will return a number between 0 and 1. multiply it with the length of your array list. then it will give you a random index value from the range 0 - your array length. you can use push method of array object to push the numbers you are generating into an empty array.
control how many times you want this to happen with a loop setting the count value by users' input.
On the webpage
http://services.runescape.com/m=itemdb_rs/Armadyl_chaps/viewitem.ws?obj=19463
It lists prices for a particular item in a game, I wanted to grab the "Current guide price:" of said item, and store it as a variable so I could output it in a google spreadsheet. I only want the number, currently it is "643.8k", but I am not sure how to grab specific text like that.
Since the number is in "k" form, that means I can't graph it, It would have to be something like 643,800 to make it graphable. I have a formula for it, and my second question would be to know if it's possible to use a formula on the number pulled, then store that as the final output?
-EDIT-
This is what I have so far and it's not working not sure why.
function pullRuneScape() {
var page = UrlFetchApp.fetch("http://services.runescape.com/m=itemdb_rs/Armadyl_chaps/viewitem.ws?obj=19463").getContentText();
var number = page.match(/Current guide price:<\/th>\n(\d*)/)[1];
SpreadsheetApp.getActive().getSheetByName('RuneScape').appendRow([new Date(), number]);
}
Your regex is wrong. I tested this one successfully:
var number = page.match(/Current guide price:<\/th>\s*<td>([^<]*)<\/td>/m)[1];
What it does:
Current guide price:<\/th> find Current guide price: and closing td tag
\s*<td> allow whitespace between tags, find opening td tag
([^<]*) build a group and match everything except this char <
<\/td> match the closing td tag
/m match multiline
Use UrlFetch to get the page [1]. That'll return an HTTPResponse that you can read with GetBlob [2]. Once you have the text you can use regular expressions. In this case just search for 'Current guide price:' and then read the next row. As to remove the 'k' you can just replace with reg ex like this:
'123k'.replace(/k/g,'')
Will return just '123'.
https://developers.google.com/apps-script/reference/url-fetch/
https://developers.google.com/apps-script/reference/url-fetch/http-response
Obviously, you are not getting anything because the regexp is wrong. I'm no regexp expert but I was able to extract the number using basic string manipulation
var page = UrlFetchApp.fetch("http://services.runescape.com/m=itemdb_rs/Armadyl_chaps/viewitem.ws?obj=19463").getContentText();
var TD = "<td>";
var start = page.indexOf('Current guide price');
start = page.indexOf(TD, start);
var end = page.indexOf('</td>',start);
var number = page.substring (start + TD.length , end);
Logger.log(number);
Then, I wrote a function to convert k,m etc. to the corresponding multiplying factors.
function getMultiplyingFactor(symbol){
switch(symbol){
case 'k':
case 'K':
return 1000;
case 'm':
case 'M':
return 1000 * 1000;
case 'g':
case 'G':
return 1000 * 1000 * 1000;
default:
return 1;
}
}
Finally, tie the two together
function pullRuneScape() {
var page = UrlFetchApp.fetch("http://services.runescape.com/m=itemdb_rs/Armadyl_chaps/viewitem.ws?obj=19463").getContentText();
var TD = "<td>";
var start = page.indexOf('Current guide price');
start = page.indexOf(TD, start);
var end = page.indexOf('</td>',start);
var number = page.substring (start + TD.length , end);
Logger.log(number);
var numericPart = number.substring(0, number.length -1);
var multiplierSymbol = number.substring(number.length -1 , number.length);
var multiplier = getMultiplyingFactor(multiplierSymbol);
var fullNumber = multiplier == 1 ? number : numericPart * multiplier;
Logger.log(fullNumber);
}
Certainly, not the optimal way of doing things but it works.
Basically I parse the html page as you did (with corrected regex) and split the string into number part and multiplicator (k = 1000). Finally I return the extracted number. This function can be used in Google Docs.
function pullRuneScape() {
var pageContent = UrlFetchApp.fetch("http://services.runescape.com/m=itemdb_rs/Armadyl_chaps/viewitem.ws?obj=19463").getContentText();
var matched = pageContent.match(/Current guide price:<.th>\n<td>(\d+\.*\d*)([k]{0,1})/);
var numberAsString = matched[1];
var multiplier = "";
if (matched.length == 3) {
multiplier = matched[2];
}
number = convertNumber(numberAsString, multiplier);
return number;
}
function convertNumber(numberAsString, multiplier) {
var number = Number(numberAsString);
if (multiplier == 'k') {
number *= 1000;
}
return number;
}
Hi I am absolute beginner of node.js Today I tried the following code
var fs, arr;
var dir, str;
var cont, item;
fs=require('fs');
cont=fs.readFileSync('unsort.txt').toString();
arr=cont.split('\n');
arr.sort();
for(str=arr.shift();str&&(item=arr.shift());)
str+='\n'+item;
fs.writeFileSync('sort_by_script.txt', str);
the above node.js code reads a file as string, from the directory of the node.exe. Splits the string by newline ('\n') to get a array. Sorts the array and prints the sorted array to the file. So as a whole the script reads a file sort the entries and saves the sorted entry in another file. The problem is the sorted order is not correct. I tried sorting the content of unsort.txt manually using MS Excel by which I got the correct order of sort. Can any one help me why the arr.sort() is not working correct. You can download unsort.txt, sort_by_script.txt, sort_by_ms_excel.txt and node.exe in the package [Sort.rar][1]
Note : unsort.txt has no numbers. All are only alphabets.
Examples from unsort.txt:
appjs
gbi
node
frame
require
process
module
WebSocket
webkitAudioContext
webkitRTCPeerConnection
webkitPeerConnection00
webkitMediaStream
MediaController
HTMLSourceElement
TimeRanges
If you do not pass a custom search function the sort function sorts lexically, numbers get cast to strings and so it happens that e.g. "10" is before "3". So the strings get sorted.
You can pass a custom function to the sort function which decides the order of the items, in case of numbers this would be an example (Be careful as numbers in your example would be strings if you dont cast / parse them to numbers) :
var numsort = function (a, b) {
return a - b;
}
var numbers = new Array(20, 2, 11, 4, 1);
var result = numbers.sort(numsort);
Another example for strings:
var sortstring = function (a, b) {
a = a.toLowerCase();
b = b.toLowerCase();
if (a < b) return 1;
if (a > b) return -1;
return 0;
}
I would use
arr.sort((obj1, obj2) => {
return obj1.localeCompare(obj2);
});
That will most likely solve your issue.