Question 309337 in Javascript Question posted in
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Javascript – How to check if array 1 has an object key from array 2 and, if not, add that object key + a new value to array 1

This code is supposed to log to the console which books + amount of each book is still at the library at the end of the day. Array 1 shows the books + amount at the start of day 1 and array 2 shows which books the library gets back ("teruggave") and which books the library loans out ("uitlening").

When the a book gets loaned out the "aantal" value of the book should go -1 while it should go +1 when the library gets a book back. The moment "aantal" reached 0, that book should be deleted from array 1. This is the part that all went well.

I also need to add the book object key "ISBN" + aantal 1 to the catalogus when that book is not at the library (so not in catalogus). I tried this but I can’t seem to get it to work. Either it keeps loading endlesly when I try to log it to the console or I get the the same book multiple times with the same "aantal" logged.

The result should be 5 books, 4 should have aantal:1 and 1 should aantal: 3.

I tried searching for an answer and tried using .include() for example to check if the ISBN[i] (so the object key it’s looking at) was available in array 1 or not. This didn’t work tho and I got the same result as I get with the code below.

for (let i = 0; i < dagverloop.length; i++) {
  for (let j = 0; j < catalogus.length; j++) {
    if (dagverloop[i].handeling === "uitlening" && dagverloop[i].ISBN === catalogus[j].ISBN) {
      catalogus[j].aantal--;
    } else if (dagverloop[i].handeling === "teruggave" && dagverloop[i].ISBN === catalogus[j].ISBN) {
      catalogus[j].aantal++;
    } else if (dagverloop[i].handeling === "uitlening" && catalogus[j].aantal === 0) {
      catalogus.splice(0, 1);
    } else if (dagverloop[i].handeling === "teruggave" && dagverloop[i].ISBN != catalogus[j].ISBN) {
      catalogus.push({
        ISBN: dagverloop[i].ISBN,
        aantal: 1
      });
    }
  }
}
console.log(catalogus);
<script>
  let catalogus = [{
      ISBN: "978-1449355739",
      aantal: 1,
    },
    {
      ISBN: "978-0596806750",
      aantal: 2,
    },
    {
      ISBN: "978-0596805524",
      aantal: 1,
    },
    {
      ISBN: "978-1491905012",
      aantal: 1,
    },
    {
      ISBN: "978-0596008642",
      aantal: 3,
    },
    {
      ISBN: "978-0596004897",
      aantal: 2,
    },
  ];
  const dagverloop = [{
      ISBN: "978-0596806750",
      handeling: "uitlening",
    },
    {
      ISBN: "978-1491905012",
      handeling: "teruggave",
    },
    {
      ISBN: "978-0596805524",
      handeling: "uitlening",
    },
    {
      ISBN: "978-1449319243",
      handeling: "teruggave",
    },
    {
      ISBN: "978-1491905012",
      handeling: "uitlening",
    },
    {
      ISBN: "978-0596004897",
      handeling: "uitlening",
    },
    {
      ISBN: "978-1491908426",
      handeling: "teruggave",
    },
    {
      ISBN: "978-1449319243",
      handeling: "uitlening",
    },
    {
      ISBN: "978-0596004361",
      handeling: "teruggave",
    },
    {
      ISBN: "978-1491905012",
      handeling: "uitlening",
    },
    {
      ISBN: "978-1449355739",
      handeling: "uitlening",
    },
  ];
</script>
Tags:

2

Answers


  1. 0

    You need to

    • Check if the book exists in the catalog.
    • If the book exists, update the count based on the operation (uitlening or teruggave).
    • If the count reaches zero, remove the book from the catalog.
    • If the book doesn’t exist and it’s a "teruggave", add the book to the catalog.
    // Find a book index by ISBN in the catalog
const findBookIndex = (catalog, isbn) => catalog.findIndex(book => book.ISBN === isbn);


dagverloop.forEach(transaction => {
  const bookIndex = findBookIndex(catalogus, transaction.ISBN);

  // If the book exists in the catalog
  if (bookIndex !== -1) {
    if (transaction.handeling === "uitlening") {
      catalogus[bookIndex].aantal--;
      // Remove it from the catalog if count reaches 0
      if (catalogus[bookIndex].aantal === 0) {
        catalogus.splice(bookIndex, 1);
      }
    } else if (transaction.handeling === "teruggave") {
      catalogus[bookIndex].aantal++;
    }
  } else {
    // If the book does not exist in the catalog and it's a "teruggave"
    if (transaction.handeling === "teruggave") {
      catalogus.push({ ISBN: transaction.ISBN, aantal: 1 });
    }
  }
});

console.log(catalogus);
    <script>
  let catalogus = [{
      ISBN: "978-1449355739",
      aantal: 1,
    },
    {
      ISBN: "978-0596806750",
      aantal: 2,
    },
    {
      ISBN: "978-0596805524",
      aantal: 1,
    },
    {
      ISBN: "978-1491905012",
      aantal: 1,
    },
    {
      ISBN: "978-0596008642",
      aantal: 3,
    },
    {
      ISBN: "978-0596004897",
      aantal: 2,
    },
  ];
  const dagverloop = [{
      ISBN: "978-0596806750",
      handeling: "uitlening",
    },
    {
      ISBN: "978-1491905012",
      handeling: "teruggave",
    },
    {
      ISBN: "978-0596805524",
      handeling: "uitlening",
    },
    {
      ISBN: "978-1449319243",
      handeling: "teruggave",
    },
    {
      ISBN: "978-1491905012",
      handeling: "uitlening",
    },
    {
      ISBN: "978-0596004897",
      handeling: "uitlening",
    },
    {
      ISBN: "978-1491908426",
      handeling: "teruggave",
    },
    {
      ISBN: "978-1449319243",
      handeling: "uitlening",
    },
    {
      ISBN: "978-0596004361",
      handeling: "teruggave",
    },
    {
      ISBN: "978-1491905012",
      handeling: "uitlening",
    },
    {
      ISBN: "978-1449355739",
      handeling: "uitlening",
    },
  ];
</script>
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  2. 0

    Using a proper data structure is 99% of success. In you case, it’s a Map ISBN => count, which you can create like this:

    let m = new Map(catalogus.map(p => [p.ISBN, p.aantal]))

    Once this is done, the rest is easy:

    for (let p of dagverloop) {
    let cur = m.get(p.ISBN) ?? 0
    m.set(p.ISBN, p.handeling === 'teruggave' ? cur + 1 : cur - 1)
}

    Now convert that map back to the list of records:

    let catalogus2 = [...m.entries()].map(p => ({ISBN: p[0], aantal: p[1]}))

    Handling zero values left as an exercise (hint: put .filter before .map above).

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