There seem to be many questions about this problem out here, but none directly relate to my question AFAICT. Here is the problem statement:
This problem is the same as the previous problem (HTTP COLLECT) in that you need to use http.get(). However, this time you will be provided with three URLs as the first three command-line arguments.
You must collect the complete content provided to you by each of the URLs and print it to the console (stdout). You don't need to print out the length, just the data as a String; one line per URL. The catch is that you must print them out in the same order as the URLs are provided to you as command-line arguments.
Here is my original solution that fails:
var http = require('http')
var concat = require('concat-stream')
var args = process.argv.slice(2, 5)
var args_len = args.length
var results = []
args.forEach(function(arg, i) {
http.get(arg, function(res) {
res.setEncoding('utf8')
res.pipe(concat(function(str) {
results[i] = str
if (results.length === args_len)
results.forEach(function(val) {
console.log(val)
})
}))
}).on('error', console.error)
})
This is the solution they recommend:
var http = require('http')
var bl = require('bl')
var results = []
var count = 0
function printResults () {
for (var i = 0; i < 3; i++)
console.log(results[i])
}
function httpGet (index) {
http.get(process.argv[2 + index], function (response) {
response.pipe(bl(function (err, data) {
if (err)
return console.error(err)
results[index] = data.toString()
count++
if (count == 3)
printResults()
}))
})
}
for (var i = 0; i < 3; i++)
httpGet(i)
What I fail to grok is the fundamental difference between my code and the official solution. I am doing the same as their solution when it comes to stuffing the replies into an array to reference later. They use a counter to count the number of callbacks while I am comparing the length of two arrays (one whose length increases every callback); does that matter? When I try my solution outside the bounds of the learnyounode program it seems to work just fine. But I know that probably means little.... So someone who knows node better than I... care to explain where I have gone wrong? TIA.
They use a counter to count the number of callbacks while I am comparing the length of two arrays (one whose length increases every callback); does that matter?
Yes, it does matter. The .length of an array depends on the highest index in the array, not the actual number of assigned elements.
The difference surfaces only when the results from the asynchronous requests come back out of order. If you first assign index 0, then 1, then 2 and so on, the .length matches the number of assigned elements and would be the same as their counter. But now try out this:
var results = []
console.log(results.length) // 0 - as expected
results[1] = "lo ";
console.log(results.length) // 2 - sic!
results[0] = "Hel";
console.log(results.length) // 2 - didn't change!
results[3] = "ld!";
console.log(results.length) // 4
results[2] = "Wor";
console.log(results.length) // 4
If you would test the length after each assignment and output the array whenever you get 4, it would print
"Hello ld!"
"Hello World!"
So it turns out there were two different issues here, one of which was pointed out by #Bergi above. The two issues are as follows:
The .length method does not actually return the number of elements in the array. Rather it returns the highest index that is available. This seems quite silly. Thanks to #Bergi for pointing this out.
The scoping of the i variable is improper, and as such the value of i can change. This causes a race condition when results come back.
My final solution ended up being as follows:
var http = require('http')
var concat = require('concat-stream')
var args = process.argv.slice(2, 5)
var args_len = args.length
var results = []
var count = 0
function get_url_save(url, idx) {
http.get(url, function(res) {
res.setEncoding('utf8')
res.pipe(concat(function(str) {
results[idx] = str
if (++count === args_len)
results.forEach(function(val) {
console.log(val)
})
}))
}).on('error', console.error)
}
args.forEach(function(arg, i) {
get_url_save(arg, i)
})
Breaking the outtermost forEach into a method call solves the changing i issue since i gets passed in as parameter by value, thus never changing. The addition of the counter solves the issue described by #Bergi since the .length method isn't as intuitive as one would imagine.
Related
I'm trying to compare a name retrieved from a JSON object, with a name as it exists on a google Sheet. Try as I might, I can't get a comparison that yields a positive.
I've tried:
IndexOf
localeCompare
==
===
I've tried
key===value
String(key)===String(value) and
String(key).valueof()=String(value).valueof.
I've also tried calling trim() on everything to make sure there are no leading/trailing white spaces (there aren't, as confirmed with a length() comparison.
As you can see from the screen shot, the values of key and value are exactly the same.
Any pointers would be gratefully received. This has held up my project for days!
Screenshot here
Description
This is not a solution but it might help find the problem. Perhaps the characters in one or the other is not what you think. Visually they compare, but what if one has a tab instead of a space. Try this, list the character codes for each and see if any character has a different value.
I've added another option that eliminates the for loop thanks to #TheMaster
Script (Option 1)
function test() {
try {
let text = SpreadsheetApp.getActiveSpreadsheet().getSheetByName("Test").getRange("A1").getValue();
console.log(text);
let code = [];
for( let i=0; i<text.length; i++ ) {
code.push(text.charCodeAt(i))
}
console.log(code.join());
}
catch(err) {
console.log(err);
}
}
Script (Option 2)
function test() {
try {
let text = SpreadsheetApp.getActiveSpreadsheet().getSheetByName("Test").getRange("A1").getValue();
console.log(text);
let code = [];
[...text].forEach( char => code.push(char.charCodeAt(0)) );
console.log(code.join());
}
catch(err) {
console.log(err);
}
}
Execution log
7:57:53 AM Notice Execution started
7:57:56 AM Info Archie White
7:57:56 AM Info 65,114,99,104,105,101,32,87,104,105,116,101
7:57:54 AM Notice Execution completed
Compare
function compare() {
const json = '{"values":[["good","bad","ugly"]]}';
const obj = JSON.parse(json);
const ss = SpreadsheetApp.getActive();
const sh = ss.getSheetByName("Sheet0");
const [hA,...vs] = sh.getDataRange().getDisplayValues();
let matches = [];
vs.forEach((r,i) => {
r.forEach((c,j) => {
let idx = obj.values[0].indexOf(c);
if(~idx) {
matches.push({row:i+1,col:j+1,index: idx});
}
})
})
Logger.log(JSON.stringify(matches))
}
Execution log
9:31:50 AM Notice Execution started
9:31:52 AM Info [{"row":1,"col":1,"index":0},{"row":2,"col":1,"index":1},{"row":3,"col":1,"index":2}]
9:31:51 AM Notice Execution completed
Sheet1:
COL1
good
bad
ugly
I want to build an if statement in which the if criteria is based on an equality test of whether a variable equals any of several values. However, I do not want to hardcode the test values, but to pass an array of values that had been randomly subset earlier.
First, I get the set of randomized values by subsetting/sampling 5 values out of an array of 15 values. Basically, I'm using this excellent solution.
function getRandomSubarray(arr, size) {
var shuffled = arr.slice(0), i = arr.length, temp, index;
while (i--) {
index = Math.floor((i + 1) * Math.random());
temp = shuffled[index];
shuffled[index] = shuffled[i];
shuffled[i] = temp;
}
return shuffled.slice(0, size);
}
var x = [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15];
var fiveRandomMembers = getRandomSubarray(x, 5);
Then, I want to pass fiveRandomMembers to test whether a variable is equal to any of the values in fiveRandomMembers's array. Then do something. To this end, I want to use this solution.
var L = function()
{
var obj = {};
for(var i=0; i<arguments.length; i++)
obj[arguments[i]] = null;
return obj;
};
if(foo in L(fiveRandomMembers)) {
/// do something
};
Unfortunately, this doesn't work for me. I must admit that the implementation of this code is within a Qualtrics survey, so the problem might be nuanced to the Qualtrics platform, and that's the reason it isn't working for me. I'm newbie to JavaScript so I apologize if this is a trivial question. But I believe that my code is problematic even in plain JavaScript (that is, regardless of Qualtrics), and I want to figure out why.
UPDATE 2020-05-24
I've been digging into this more deeply, and I have some insights. This looks more like a qualtrics problem rather than plain JS issue. However, the underlying problem might still have to do with some JS mechanism, and that's why I bother to update it here -- maybe someone will know what's causing this behavior.
To recap -- I want to condition an action based on whether a given variable's content matches either of the values in an array. I've tried using both includes and indexOf, but either method fails. The problem boils down to the functions not doing an exact match. For example, if I have an array of 5 numbers such as 8, 9, 12, 13, 14, and I want to test whether 4 exists in the array, then an exact match should return FALSE. However, both indexOf and contains return TRUE because 14 has 4 in it. This is not an exact matching then. Furthermore, I've tried to investigate what is the position indexOf would return for such a false-positive match. Typically, it would return a position that is even larger than the total length of the array, making no sense whatsoever. Here's an example from my Qualtrics survey, demonstrating the problem:
The code giving this is comprised of two qualtrics questions:
(-) First piece
Qualtrics.SurveyEngine.addOnReady(function()
{
/*Place your JavaScript here to run when the page is fully displayed*/
function getRandomSubarray(arr, size) {
var shuffled = arr.slice(0), i = arr.length, temp, index;
while (i--) {
index = Math.floor((i + 1) * Math.random());
temp = shuffled[index];
shuffled[index] = shuffled[i];
shuffled[i] = temp;
}
return shuffled.slice(0, size);
}
var x = [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15];
var fiveRandomMembers = getRandomSubarray(x, 5);
if (Array.isArray(fiveRandomMembers)) Qualtrics.SurveyEngine.setEmbeddedData('is_array', "TRUE");
Qualtrics.SurveyEngine.setEmbeddedData('length', fiveRandomMembers.length);
Qualtrics.SurveyEngine.setEmbeddedData('five_sampled_numbers', fiveRandomMembers);
});
(-) Second piece
Qualtrics.SurveyEngine.addOnReady(function()
{
jQuery("#"+this.questionId).find('.QuestionText:first').css("padding-bottom", "0px");
var currentLoopNum = "${lm://CurrentLoopNumber}";
// var currentLoopNum = parseInt(currentLoopNum, 10); // tried converting to numeric but it doesn't solve the problem
var fiveSampledNumbers = "${e://Field/five_sampled_numbers}";
if (fiveSampledNumbers.includes(currentLoopNum)) {
Qualtrics.SurveyEngine.setEmbeddedData('does_loop_number_appear', "Yes");
} else {
Qualtrics.SurveyEngine.setEmbeddedData('does_loop_number_appear', "No");
}
Qualtrics.SurveyEngine.setEmbeddedData('index_of', fiveSampledNumbers.indexOf(currentLoopNum));
});
Here is a link to the Qualtrics survey, demonstrating the problem, in case it's helpful for troubleshooting: link
However, when testing the same code outside of Qualtrics, the problem doesn't replicate.
Does someone have a clue or even a hypothesis what could be the problem with the matching? Even if you're not necessarily familiar with Qualtrics...
I've never worked with Qualtrics before, but to me it is clear that the line
var fiveSampledNumbers = "${e://Field/five_sampled_numbers}";
will assign a string value to fiveSampledNumbers, not an array value.
Indeed, if you attempt to run the checks you are making on a string rather than an array, you get the unexpected results you saw above, because you are doing string operations rather than array operations:
var fiveSampledNumbers = "6,4,10,11,15";
console.log(fiveSampledNumbers.includes(5)); // logs true (string ends with the character "5")
console.log(fiveSampledNumbers.indexOf(5)); // logs 11 (index of the character "5")
To get around this, you will have to split the string by commas and parse each number within it:
var fiveSampledNumbers = "6,4,10,11,15";
fiveSampledNumbers = fiveSampledNumbers.split(",").map(function (n) { return parseInt(n, 10); });
console.log(fiveSampledNumbers.includes(5)); // logs false
console.log(fiveSampledNumbers.indexOf(5)); // logs -1
I'm trying to implement the quickSort algorithm in javascript, i have to extract 10,000 numbers from a txt file, pass them into an array, and pass this as an argument of my quickSort function, using the fs module of nodejs. The code is able to read the 10,000 numbers, and to convert them from an array of string to an array of number, but when i try to pass the array into my function, only 3472 numbers are passed, which i don't understand.
const fs = require('fs');
// Reading the data from the file containing the 10,000 numbers
const file = fs.readFileSync('./quickSort.txt', 'utf-8');
//Checking if it has read all the numbers correctly
console.log(file); // Displays the 10,000 numbers as strings in an array
// Convert them from string to integer
const finalFile = file.split('\n').map(e => {
return parseInt(e, 10);
})
// Checking if it has converted each element of the array to an integer
//console.log(finalFile) displays the array, with the 10,000 elements converted to integers
// Initialize a counter for the comparaisons made by the quickSort algorithm
let comparisons = 0;
// Sort them using quick sort
function quick_Sort(origArray) {
if (origArray.length <= 1) {
return origArray;
} else {
// Checking if the array has been correctly passed as an argument
console.log(origArray.length); //Displays 3742 instead of 10,000
var left = [];
var right = [];
var newArray = [];
var pivot = origArray.pop();
var length = origArray.length;
// I have tried comparisons += length - 1; too, but i doesn't work
comparisons += length;
for (var i = 0; i < length; i++) {
if (origArray[i] <= pivot) {
left.push(origArray[i]);
} else {
right.push(origArray[i]);
}
}
for (var i = 0; i < right.length; i++) {
comparisons++;
if (right[i] < pivot) {
return right.splice(i, 0, pivot);
}
}
return newArray.concat(quick_Sort(left), quick_Sort(right));
}
}
// Display the result
const result = quick_Sort(finalFile);
// expected output: 25
console.log(result);
Thank you very much.
Edit: In fact the problem of the size comes from the last for loop of the function, if i delete it, and insert the pivot between like that, it works (thanks to StardustGogeta) :
return newArray.concat(quick_Sort(left), pivot, quick_Sort(right));
This is a logical error. You need to change
return newArray.concat(quick_Sort(left), quick_Sort(right));
to
return newArray.concat(quick_Sort(left), pivot, quick_Sort(right));
With that change, the program works for me. The problem is that you are accidentally getting rid of (via .pop()) approximately 1/3 of your input values (the pivot values) during sorting.
try this:
const finalFile = file.split('\r?\n').map(.....)
Your parsing code works for me except for one issue: parseInt returns NaN for the last new line so you need to remove the last element from the array like this: finalFile.pop();. However this does not explain why you are seeing such a difference in the number of elements. There must be something different either in the code or the file you posted.
Ok, the following code works correctly for me, it is the usual way I do asynchronous loops (count is async). So before callbacking I get 3 numbers logged, in principle different.
var arrayIds = ['a', 'b', 'c'];
var totalIds = arrayIds.length;
var done = 0;
var count = 0;
for (var i = 0; i < arrayIds.length; i++) {
mongoose.Model.count({ 'likes.id': arrayIds[i] }, function (err, c) {
count += c;
console.log(c);
if (++done < totalIds) return; //else
callback(count);
})
}
BUT I don't know what is happening in this other case, with the same philosophy, please help:
var arrayIds = ['a', 'b', 'c'];
var totalIds = arrayIds.length;
var done = 0;
var likesPartial = [];
for (var m = 0; m < arrayIds.length; m++) {
likesPartial.push(arrayIds[m]);
profiles.count({ 'likes.id': { $in: likesPartial } }, function (err, u){
console.log(u);
if (++done < totalIds) return; //else
callback(u);
})
}
The problem is that I get the same 3 numbers logged (with the value of the expected last 'u', the one callbacked in the end), while they should in principle be different, because likesPartial array has at each step a different number of elements.
The two examples seem analogous to me, that's why I can't find the error.
Thanks.
In your first example, you're updating count with each callback and when the last callback comes in, you're calling callback with the final result in count. Which makes sense.
Your second example is markedly different: It receives multiple values but ignores all but the last one (other than logging them), and then calls callback with just the last u it receives. So the previous us it received are thrown away, which doesn't immediately seem to make sense (not least because you can't know which u it is, assuming the operation is asynchronous; they could complete in any order).
Another thing I noted is this:
profiles.count({ 'likes.id': { $in: likesPartial } }, function (err, u){
// ----------------------------^^^^^^^^^^^^^^^^^
You're passing in the array of likesPartial each time, whereas in your first code snippet, you're passing a single ID (arrayIds[i]), not an array.
Situation
I'm currently writing a javascript widget that displays a random quote into a html element. the quotes are stored in a javascript array as well as how many times they've been displayed into the html element. A quote to be displayed cannot be the same quote as was previously displayed. Furthermore the chance for a quote to be selected is based on it's previous occurences in the html element. ( less occurrences should result in a higher chance compared to the other quotes to be selected for display.
Current solution
I've currently made it work ( with my severely lacking javascript knowledge ) by using a lot of looping through various arrays. while this currently works ( !! ) I find this solution rather expensive for what I want to achieve.
What I'm looking for
Alternative methods of removing an array element from an array, currently looping through the entire array to find the element I want removed and copy all other elements into a new array
Alternative method of calculating and selecting a element from an array based on it's occurence
Anything else you notice I should / could do different while still enforcing the stated business rules under Situation
The Code
var quoteElement = $("div#Quotes > q"),
quotes = [[" AAAAAAAAAAAA ", 1],
[" BBBBBBBBBBBB ", 1],
[" CCCCCCCCCCCC ", 1],
[" DDDDDDDDDDDD ", 1]],
fadeTimer = 600,
displayNewQuote = function () {
var currentQuote = quoteElement.text();
var eligibleQuotes = new Array();
var exclusionFound = false;
for (var i = 0; i < quotes.length; i++) {
var iteratedQuote = quotes[i];
if (exclusionFound === false) {
if (currentQuote == iteratedQuote[0].toString())
exclusionFound = true;
else
eligibleQuotes.push(iteratedQuote);
} else
eligibleQuotes.push(iteratedQuote);
}
eligibleQuotes.sort( function (current, next) {
return current[1] - next[1];
} );
var calculatePoint = eligibleQuotes[0][1];
var occurenceRelation = new Array();
var relationSum = 0;
for (var i = 0; i < eligibleQuotes.length; i++) {
if (i == 0)
occurenceRelation[i] = 1 / ((calculatePoint / calculatePoint) + (calculatePoint / eligibleQuotes[i+1][1]));
else
occurenceRelation[i] = occurenceRelation[0] * (calculatePoint / eligibleQuotes[i][1]);
relationSum = relationSum + (occurenceRelation[i] * 100);
}
var generatedNumber = Math.floor(relationSum * Math.random());
var newQuote;
for (var i = 0; i < occurenceRelation.length; i++) {
if (occurenceRelation[i] <= generatedNumber) {
newQuote = eligibleQuotes[i][0].toString();
i = occurenceRelation.length;
}
}
for (var i = 0; i < quotes.length; i++) {
var iteratedQuote = quotes[i][0].toString();
if (iteratedQuote == newQuote) {
quotes[i][1]++;
i = quotes.length;
}
}
quoteElement.stop(true, true)
.fadeOut(fadeTimer);
setTimeout( function () {
quoteElement.html(newQuote)
.fadeIn(fadeTimer);
}, fadeTimer);
}
if (quotes.length > 1)
setInterval(displayNewQuote, 10000);
Alternatives considered
Always chose the array element with the lowest occurence.
Decided against this as this would / could possibly reveal a too obvious pattern in the animation
combine several for loops to reduce the workload
Decided against this as this would make the code to esoteric, I'd probably wouldn't understand the code anymore next week
jsFiddle reference
http://jsfiddle.net/P5rk3/
Update
Rewrote my function with the techniques mentioned, while I fear that these techniques still loop through the entire array to find it's requirements, at least my code looks cleaner : )
References used after reading the answers here:
http://www.tutorialspoint.com/javascript/array_map.htm
http://www.tutorialspoint.com/javascript/array_filter.htm
http://api.jquery.com/jQuery.each/
I suggest array functions that are mostly supported (and easily added if not):
[].splice(index, howManyToDelete); // you can alternatively add extra parameters to slot into the place of deletion
[].indexOf(elementToSearchFor);
[].filter(function(){});
Other useful functions include forEach and map.
I agree that combining all the work into one giant loop is ugly (and not always possible), and you gain little by doing it, so readability is definitely the winner. Although you shouldn't need too many loops with these array functions.
The answer that you want:
Create an integer array that stores the number of uses of every quote. Also, a global variable Tot with the total number of quotes already used (i.e., the sum of that integer array). Find also Mean, as Tot / number of quotes.
Chose a random number between 0 and Tot - 1.
For each quote, add Mean * 2 - the number of uses(*1). When you get that that value has exceeded the random number generated, select that quote.
In case that quote is the one currently displayed, either select the next or the previous quote or just repeat the process.
The real answer:
Use a random quote, at the very maximum repeat if the quote is duplicated. The data usages are going to be lost when the user reloads/leaves the page. And, no matter how cleverly have you chosen them, most users do not care.
(*1) Check for limits, i.e. that the first or last quota will be eligible with this formula.
Alternative methods of removing an array element from an array
With ES5's Array.filter() method:
Array.prototype.without = function(v) {
return this.filter(function(x) {
return v !== x;
});
};
given an array a, a.without(v) will return a copy of a without the element v in it.
less occurrences should result in a higher chance compared to the other quotes to be selected for display
You shouldn't mess with chance - as my mathematician other-half says, "chance doesn't have a memory".
What you're suggesting is akin to the idea that numbers in the lottery that haven't come up yet must be "overdue" and therefore more likely to appear. It simply isn't true.
You can write functions that explicitly define what you're trying to do with the loop.
Your first loop is a filter.
Your second loop is a map + some side effect.
I don't know about the other loops, they're weird :P
A filter is something like:
function filter(array, condition) {
var i = 0, new_array = [];
for (; i < array.length; i += 1) {
if (condition(array[i], i)) {
new_array.push(array[i]);
}
}
return new_array;
}
var numbers = [1,2,3,4,5,6,7,8,9];
var even_numbers = filter(numbers, function (number, index) {
return number % 2 === 0;
});
alert(even_numbers); // [2,4,6,8]
You can't avoid the loop, but you can add more semantics to the code by making a function that explains what you're doing.
If, for some reason, you are not comfortable with splice or filter methods, there is a nice (outdated, but still working) method by John Resig: http://ejohn.org/blog/javascript-array-remove/