Basically i have to create a quiz with 3category. each with 5questions.
I would have to push the selected category-questions into this new array from the array with all the questions. I am unable to do so.
pushSelectedQuestion() {
for (var i = 0; i < this.getNumberOfQuestion; i++) {
if (usercategory == questionPool[i].category) {
mcqSelected.push(questionPool[i])
return mcqSelected;
}
}
}
usercategory = input from user.
if user chooses category 1.
if (1 == questionPool[1].category) (if it matches the category) then it will be pushed.
This is the part which i cant do
Well, from the information you've provided, there's one main issue here - the return statement is definitely shortcutting the loop - so even if you have everything else right, you'll only ever get the first matching question. The rest will have been cut out by the return statement, which stops the function and returns the value.
pushSelectedQuestion() {
for (var i = 0; i < this.getNumberOfQuestion; i++) {
if (usercategory == questionPool[i].category) {
mcqSelected.push(questionPool[i])
// the below line is causing this loop to end after the first time through the list.
// Remove it and then put a console.log(mcqSelected);
// here instead to see the value during each iteration of the loop.
return mcqSelected;
}
}
}
There are a lot of ways to accomplish what you want to do here though. For example, you could just use the javascript Array.filter method like so
let selectedQuestions = questionPool.filter(question => question.category == userCategory)
Maybe I am not understanding your question correctly, but can't you use nested arrays. If the questions are categorized beforehand that is.
Related
I have this exercise that already got the answer, but after hearing the explanations, still don't understand. This is the exercise:
"write a function isUniform() which takes an array as an argument and
returns true if all elements in the array are identical"
This is the solution
function isUniform(numArr) {
var first = numArr[0];
for (var i = 1; i < numArr.length; i++) {
if (numArr[i] !== first) {
return false;
}
}
return true;
}
I got it almost right, but i did a else statement with the "return true" and it didn't work. Why does it work with the "return true" outside of the for loop?
(edited) This is how i did the first time:
function isUniform(numArr) {
var first = numArr[0];
for (var i = 1; i < numArr.length; i++) {
if (numArr[i] !== first) {
return false;
}
else {
return true;
}
}
}
If you return true outside the loop, then it checks every element in the loop until one matches the if test or it gets to the end of the loop.
If you return true inside the loop then it will always hit a return statement for the first element and then stop the loop.
I got it almost right, but i did a else statement with the "return
true" and it didn't work
The solution below would return the wrong results in some cases because all it does is find the first element within the array that's equal to first variable and return true, even though it hasn't searched the entire array.
function isUniform(numArr) {
var first = numArr[0];
for (var i = 1; i < numArr.length; i++) {
if (numArr[i] !== first) {
return false;
}
else {
return true;
}
}
}
I have this exercise that already got the answer, but after hearing
the explanations, still don't understand.
let's assume this is your array:
[10,10,13,10,10]
let's assume this is the variable first:
first = 10;
The if statement below which is within the for loop basically says if the variable first ( 10 ) is not equal to the element at the current index i (nth number within the array) then return false. This makes sense because if at this moment the variable first is not the same with the element at the specified index for example index 2 (number 13) then there is no point to carry on. Hence, it will return false.
if (numArr[i] !== first) {
return false;
}
now let's assume the array is:
[10,10,10,10,10]
let's assume this is the variable first:
first = 10;
now the variable first will be compared against each elementwithin the array and it says "is 10 not equal to the current element". in this case that's false because 10 is equal to 10. This will propagate down the array and control will never pass inside the if block. Eventually, control passes down to the return true statement.
if (numArr[i] !== first) {
return false;
}
It works because is the final statement in your function. Basically your function will return true if the condition inside for loop will not be triggered
Let's say you've got a broken printer which once in a while messes the printout. Now you printed 20 copies and want to know if every paper is fine. So now you would have to iteratively compare every copy until you found one which is not matching (and know it's time to get a new printer?). Or you've gone the way through the hole stack and know every copy is fine (and you've wasted time for nothing).
I have searched high and low, not only on StackOverflow, but many other places elsewhere on the web. I've tried what seems like everything, but something is fundamentally flawed with my logic. I apologize for introducing another "Duplicates in Array" question, but I am stuck and nothing seems to be working as expected.
Anyway, I have a multi-dimensional JavaScript array, only 2 levels deep.
var array = [[Part #, Description, Qty:],
[Part #, Description, Qty:],
[Part #, Description, Qty:]]; //etc
What I need to do is create a function that searches array and returns any duplicate "Part #" lines. When they are returned, I would like to have the entire inner array returned, complete with description and qty.
The trick with this is that the Part #'s that would qualify as 'duplicate' would end differently (specifically the last 4 characters), so using String.prototype.substr makes sense (to me).
I know there are duplicates in the array in the way that I am looking for, so I know that if I had the solution, it would return those Part #'s.
Here is what I have tried so far that gets me the closest to a solution:
function findDuplicateResults(arr) {
var result = [];
for (var i = 0; i < arr.length; i++) {
if (arr[i][0].substr(0,5) === arr[++i][0].substr(0,5)) {
result.push(arr[i]);
}
}
return console.log(result);
}
My thinking is that if the element in the array(with substr(0,5) is equal to the next one in line, push that to the result array. I would need the other duplicate in there too. The point of the code is to show only dupes with substr(0,5).
I have tried using Higher Order Functions such as map, forEach, reduce, and filter (filter being the one that boggles my mind as to why it doesn't do what I want), but I have only been able to return [] or the entire array that way. The logic that I use for said Higher Order Functions remains the same (which is probably the problem here).
I am expecting that my if condition is where the most of the problem is. Any pointers or solutions are greatly appreciated.
There is a mistake in your code. When you use ++i, you are changing the value of i, so it is going to skip one item in the next iteration.
Regarding the logic, you are only comparing one item to the next item, when you should really be comparing each item to all items:
function findDuplicateResults(arr) {
var result = [];
for (var i = 0; i <= arr.length - 1; i++) {
for (var k = 0; k <= arr.length - 1; k++) {
if (i !== k && arr[i][0].substr(0,5) === arr[k][0].substr(0,5)) {
result.push(arr[i]);
}
}
}
return result;
}
Although, the 'substr' could be dropped, and 'for' loop could be replaced by a higher order function:
function findDuplicateResults(arr) {
return arr.filter(function(item1){
return arr.filter(function(item2){
return item1[0] === item2[0];
}).length > 1;
});
}
I'm doing an assignment that requires us to add objects to a fake cart array from a fake database array, then go to a cart page that displays everything in the "cart." Now, that's all well and good, but for some reason I can't get more than one object to show up in the fakeCart array.
I'm fairly certain the issue is in this function, because everything displays properly otherwise in every way.
So, it turns out I posted code that I was tinkering with. I've since updated it to the almost-working one.
function addToCart(e) {
'use strict';
var fakeCart = [];
for (var i = 0; i < fakeDatabase.length; i++) {
if (fakeDatabase[i].id == e.currentTarget.id) {
fakeCart.push(fakeDatabase[i]);
}
}
sessionStorage.fakeCart = JSON.stringify(fakeCart);
}
Essentially, I can get the code to make a single object go from one array (database) to the other (cart), but whenever I try to add one back in it just replaces the last one.
The code overwrites any existing value of sessionStorage.fakeCart, so there will never be more than one element in the serialized array. You can fix that by reading the value from sessionStorage instead of creating a new list each time.
function addToCart(e, productNum) {
'use strict';
// change this
var fakeCart = JSON.parse(sessionStorage.fakeCart) || [];
for (var i = 0; i < fakeDatabase.length; i++) {
if (fakeDatabase[i].id == e.currentTarget.id) {
// and this
fakeCart.push(fakeDatabase[i]);
}
}
sessionStorage.fakeCart = JSON.stringify(fakeCart);
}
I think :
Instead of
fakeCart[i].push(fakeDatabase[i]);
you require this
fakeCart.splice(i, 0, fakeDatabase[i]);
I pass 2 arrays to a function and want to move a specific entry from one array to another. The moveDatum function itself uses underscorejs' methods reject and filter. My Problem is, the original arrays are not changed, as if I was passing the arrays as value and not as reference. The specific entry is correctly moved, but as I said, the effect is only local. What do I have to change, to have the original arrays change as well?
Call the function:
this.moveDatum(sourceArr, targetArr, id)
Function itself:
function moveDatum(srcDS, trgDS, id) {
var ds = _(srcDS).filter(function(el) {
return el.uid === uid;
});
srcDS = _(srcDS).reject(function(el) {
return el.uid === uid;
});
trgDS.push(ds[0]);
return this;
}
Thanks for the help
As mentioned in the comments, you're assigning srcDS to reference a new array returned by .reject(), and thus losing the reference to the array originally passed in from outside the function.
You need to perform your array operations directly on the original array, perhaps something like this:
function moveDatum(srcDS, trgDS, id) {
var ds;
for (var i = srcDS.length - 1; i >= 0; i--) {
if (srcDS[i].uid === id) {
ds = srcDS[i];
srcDS.splice(i,1);
}
}
trgDS.push(ds);
return this;
}
I've set up the loop to go backwards so that you don't have to worry about the loop index i getting out of sync when .splice() removes items from the array. The backwards loop also means ds ends up referencing the first element in srcDS that matches, which is what I assume you intend since your original code had trgDS.push(ds[0]).
If you happen to know that the array will only ever contain exactly one match then of course it doesn't matter if you go forwards or backwards, and you can add a break inside the if since there's no point continuing the loop once you have a match.
(Also I think you had a typo, you were testing === uid instead of === id.)
Copy over every match before deleting it using methods which modify Arrays, e.g. splice.
function moveDatum(srcDS, trgDS, id) { // you pass an `id`, not `uid`?
var i;
for (i = 0; i < srcDS.length; ++i) {
if (srcDS[i].uid === uid) {
trgDS.push(srcDS[i]);
srcDS.splice(i, 1);
// optionally break here for just the first
i--; // remember; decrement `i` because we need to re-check the same
// index now that the length has changed
}
}
return this;
}
I have been working on creating a custom script to help manage a secret questions form for a login page. I am trying to make all the seperate select lists dynamic, in that if a user selects a question in one, it will no longer be an option in the rest, and so on. Anyways, the problem I am having is when I try to set the variables in the other lists to null. I am currently working with only 3 lists, so I look at one list, and find/delete matches in the other 2 lists. Here is my loop for deleting any matches.
for(i=0; i<array1.length; i++) {
if(array2[i].value == txtbox1.value) {
document.questions.questions2.options[i] = null
}
if(array3[i].value == txtbox1.value) {
document.questions.questions3.options[i] = null
}
}
This works fine if both the matches are located at the same value/position in the array. But if one match is at array1[1] and the other match is at array3[7] for example, then only the first match gets deleted and not the second. Is there something I am missing? Any help is appreciated. Thanks!
I don't see too many choices here, considering that the position in each array can vary.
Do it in separate loops, unless of course you repeat values in both arrays and share the same position
EDTI I figured out a simple solution, it may work, create a function. How about a function wich recives an array as parameter.
Something like this:
function finder(var array[], var valueToFound, var question) {
for (i=0; i<array.lenght; i++) {
if (array[i].value == valueToFound) {
switch (question) {
case 1: document.questions.questions1.options[i] = null;
break;
}
return;
}
}
}
I think i make my point, perhaps it can take you in the right direction
My bet is that the code isn't getting to array3[7] because either it doesn't exist or that array2 is too short and you're getting a JavaScript exception that's stopping the code from doing the check. Is it possible that array2 and array3 are shorter than array1?
It is more code, but I would do it like this:
var selectedvalue == txtbox1.value;
for(i=0; i<array2.length; i++) { // iterate over the length of array2, not array1
if(array2[i].value == selectedvalue) {
document.questions.questions2.options[i] = null;
break; // found it, move on
}
}
for(i=0; i<array3.length; i++) {
if(array3[i].value == selectedvalue) {
document.questions.questions3.options[i] = null;
break; // you're done
}
}