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Filter an array from another array of elements and return specific positions

I'm finally learning better methods for my JS. I'm trying to find a way to go faster than I do so far :
In my code, I have two arrays :
one with unique keys in first position
one with those keys in first position but not unique. There are multiple entries with a certain value I want to filter.
The thing is I don't want to filter everything that is in the second array. I want to select some positions, like item[1]+item[5]+item[6]. What I do works, but I wonder if there isn't a faster way to do it ?
for (let i=0;i<firstArrayOfUniques.length;i++){
const findRef = secondArrayOfMultiple
.filter(item => item[0]==firstArrayOfUniques[i][0]);
// Afterwards, I redo a map and select only the second element,
//then I join the multiple answers
// Is there a way to do all that in the first filter?
const refSliced = findRef.map(x=>x[1]);
const refJoin = refSliced.join(" - ");
canevasSheet.getRange(1+i,1).setValue(refJoin);
}

The script snippet you quote will spend almost all of its running time calling the Range.setValue() method. It gets called separately for every data row. Use Range.setValues() instead, and call it just once, like this:
function moot(firstArrayOfUniques, secondArrayOfMultiple) {
const result = firstArrayOfUniques.map(uniqueRow =>
secondArrayOfMultiple
.filter(row => row[0] === uniqueRow[0])
.map(row => row[1])
.join(' - '));
canevasSheet.getRange(1, 1, result.length, result[0].length).setValues(result);
}
See Apps Script best practices.

Is there a way to combine map and shift in Javascript?

I'm working with a buffer array that I am periodically checking. When I am mapping through the elements, I would like access the element using the shift method, this way I would get the next element in the array and would also remove it. Is there a way to do this in a map? Thank you!
I currently have a naive solution, which is prone to race conditions.
if (timestep) {
bufferArray.map((mvt) =>{
console.log(mvt)
});
bufferArray = [];
}

As I would like to go through the elements of the array one by one and remove the current element from the array. For this reason a simple and great solution is to use a while loop with the shift method. For example:
let arr = [0,1,2,3,4,5];
while (arr.length)
{
let current = arr.shift()
// do something with current
}

WebdriverIO loop through element list

So I have a table of 250 of rows, and I want to just get all the values from one column and check if they meet the required criteria:
const rows = browser.elements(selector..);
const numbers = [];
rows.value.forEach(cellData => {
const value = browser.elementIdText(cellData.value.ELEMENT).value;
// some logic to check if the value is ok
numbers.push(value);
});
// check if all numbers are sorted correctly
, but it most of the time it fails on the line (it says stale element reference: element is not attached to the page document):
const value = browser.elementIdText(cellData.value.ELEMENT).value;
I tried doing cellDate.getText(), but there was a Java socket error, could someone help? I assume the selector is not attached to the page as indicated, but I can't figure my head out how to just loop through them all.

I had a solution similar to your method before and while it seems to work, I think there might just be some slight adjustments to your code to get what you want. I never had much luck chaining from the end of the elementIdText call.
Step 1: Grab all the Data (browser.elements or browser.$$):
let cellData = browser.$$('selector that matches desired Column Data')
The above returns an array of JSON WebElements. And as you know you can correctly loop through the array looking at the "values". If you use the selector that matches the Column Values you're looking for you should have all similar data stored in the element.value.ELEMENT.
Step 2: Loop through the cellData array and pluck out the text values of the ELEMENT using browser.elementIdText()
cellData.forEach((elem) => {
let number = browser.elementIdText(elem.value.ELEMENT)
//elementIdText also returns a JSON WebElement so it's number.value
if(number.value === <condition>) {
console.log('number looks good')
//perform other on value logic
}
})
//perform other logic still in loop EX: array.push()
})
I hope this helps! Let me know if you hit any snags!

Complex challenge about complexity and intersection

Preface
Notice: This question is about complexity. I use here a complex design pattern, which you don't need to understand in order to understand the question. I could have simplified it more, but I chose to keep it relatively untouched for the sake of preventing mistakes. The code is written in TypeScript which is a super-set of JavaScript.
The code
Regard the following class:
export class ConcreteFilter implements Filter {
interpret() {
// rows is a very large array
return (rows: ReportRow[], filterColumn: string) => {
return rows.filter(row => {
// I've hidden the implementation for simplicity,
// but it usually returns either an empty array or a very short one.
}
}).map(row => <string>row[filterColumn]);
}
}
}
It receives an array of report row, then it filters the array by some logic that I've hidden. Finally it does not return the whole row, but only one stringy column that is mentioned in filterColumn.
Now, take a look at the following function:
function interpretAnd (filters: Filter[]) {
return (rows: ReportRow[], filterColumn: string) => {
var runFilter = filters[0].interpret();
var intersectionResults = runFilter(rows, filterColumn);
for (var i=1; i<filters.length; i++) {
runFilter = filters[i].interpret();
var results = runFilter(rows, filterColumn);
intersectionResults = _.intersection(intersectionResults, results);
}
return intersectionResults;
}
}
It receives an array of filters, and returns a distinct array of all the "filterColumn"s that the filters returned.
In the for loop, I get the results (string array) from every filter, and then make an intersection operation.
The problem
The report row array is large so every runFilter operation is expensive (while on the other hand the filter array is pretty short). I want to iterate the report row array as fewer times as possible. Additionally, the runFilter operation is very likely to return zero results or very few.
Explanation
Let's say that I have 3 filters, and 1 billion report rows. the internal iterration, i.e. the iteration in ConcreteFilter, will happen 3 billion times, even if the first execution of runFilter returned 0 results, so I have 2 billion redundant iterations.
So, I could, for example, check if intersectionResults is empty in the beginning of every iteration, and if so, then break the loop. But I'm sure that there are better solutions mathematically.
Also if the first runFIlter exectuion returned say 15 results, I would expect the next exectuion to receive an array of only 15 report rows, meaning I want the intersection operation to influence the input of the next call to runFilter.
I can modify the report row array after each iteration, but I don't see how to do it in an efficient way that won't be even more expensive than now.
A good solution would be to remove the map operation, and then passing the already filtered array in each operation instead of the entire array, but I'm not allowed to do it because I must not change the results format of Filter interface.
My question
I'd like to get the best solution you could think of as well as an explanation.
Thanks a lot in advance to every one who would spend his time trying to help me.

Not sure how effective this will be, but here's one possible approach you can take. If you preprocess the rows by the filter column you'll have a way to retrieve the matched rows. If you typically have more than 2 filters then this approach may be more beneficial, however it will be more memory intensive. You could branch the approach depending on the number of filters. There may be some TS constructs that are more useful, not very familiar with it. There are some comments in the code below:
var map = {};
// Loop over every row, keep a map of rows with a particular filter value.
allRows.forEach(row => {
const v = row[filterColumn];
let items;
items = map[v] = map[v] || [];
items.push(row)
});
let rows = allRows;
filters.forEach(f => {
// Run the filter and return the unique set of matched strings
const matches = unique(f.execute(rows, filterColumn));
// For each of the matched strings, go and look up the remaining rows and concat them for the next filter.
rows = [].concat(...matches.reduce(m => map[v]));
});
// Loop over the rows that made it all the way through, extract the value and then unique() the collection
return unique(rows.map(row => row[filterColumn]));
Thinking about it some more, you could use a similar approach but just do it on a per filter basis:
let rows = allRows;
filters.forEach(f => {
const matches = f.execute(rows, filterColumn);
let map = {};
matches.forEach(m => {
map[m] = true;
});
rows = rows.filter(row => !!map[row[filterColumn]]);
});
return distinctify(rows.map(row => row[filterColumn]));

Get four unique items and add them to an array

I’m 100% certain this code has been working before. Now it strangely doesn’t.
The goal is to create a multiple choice quiz for a flashcard. I create an array to store the card's ids: the first one goes the current card id, then three other random ones. My goal is to make sure they don’t repeat either the first card or themselves.
This is how I do it:
// Array of cards’ ids to use
var randomCardsIds = [];
// Get the active card’s element id, add it to the array
randomCardsIds[0] = this.activeCardId;
// Get the current cards collection
var allCurrentCards = this.carouselEl.items.items;
// Get three random ids of other cards
var i = 0
while (i<3) {
// Get a random card element
var randomCardEl = allCurrentCards[Math.floor(Math.random() * allCurrentCards.length)];
// Get its id
var randomCardElId = randomCardEl.body.down('.card').id;
randomCardElId = randomCardElId.substring(randomCardElId.indexOf('_')+1);
console.log(randomCardElId, randomCardsIds, randomCardsIds.indexOf(randomCardElId));
// Make sure it is not in the array yet, and then add it
if (randomCardsIds.indexOf(randomCardElId) == -1) {
randomCardsIds.push(randomCardElId);
i++;
}
// Otherwise, the loop will have to run again
}
Basically, in a loop, for each item I check whether it already exists in the array or not. If it doesn’t, push it to the array, otherwise, run the loop again. Here is the console logging result:
Well, the first thing: it always shows the final state of the array: as if it is already filled with the results, which is weird. But the most important thing: the script does not recognise a duplicate (e.g. in the first result, 74 is repeated, and in the second to last, 47).
It only returns something different then -1, when it finds a match in the second position (returns 1, obviously). When a match is in a different position in the array, it always returns -1.
What am I doing wrong here?

Are you testing this in IE6? The problem is indexOf doesnot work with IE6.
For alternative you can check Best way to find if an item is in a JavaScript array?

A variation on a shuffling algoruthm seems to be the best bet here.