Question 230816 in Javascript Question posted in
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Javascript – Checking duplicate objects in array with some and 2 conditions

I have data from a form that needs to be compared to its older data.
I want to check if an object was in the previous old data and if its slot number changed.

Data example

const oldData = [{name: "John", slot: 2}, {name: "John", slot: 3}, {name: "John", slot: 4}]
const newData = [{name: "Alex", slot: 2}, {name: "John", slot: 3}, {name: "Bob", slot: 4}, {name: "John", slot: 5}]

  // Duplications
  const duplicateCreate = newData.filter((order1) => {
    return oldData.some((order2) => {
      return (
        order1.name === order2.name &&
        order1.slot !== order2.slot
      );
    });
  });

  console.log(duplicateCreate)

What I expect the output to be

[{name: "John", slot: 5}]

What I get

[{name: "John", slot: 3}, {name: "John", slot: 5}]

I have no Idea why the some function is passing john slot 2 as truthy, if I change my code to
order1.slot === order2.slot then the output will be

[{name: "John", slot: 3}]

So clearly its reading the && condition and clearly that logic works but the logic of checking for the object whose name is john and slot !== the same isnt working the way its written from my understanding so I am kind of at a loss right now.

Tags:

3

Answers


  1. 0

    I ran a couple of scenarios and this works fine:

    const oldData = [{name: "John", slot: 2}, {name: "John", slot: 3}, {name: "John", slot: 4}];
const newData = [{name: "Alex", slot: 2}, {name: "John", slot: 3}, {name: "Bob", slot: 4}, {name: "John", slot: 5}];

const duplicateCreate = newData.filter((order1) => {
  const exactMatch = oldData.some(order2 => order1.name === order2.name && order1.slot === order2.slot);
  const nameMatch = oldData.some(order2 => order1.name === order2.name);

  return nameMatch && !exactMatch;
});

console.log(duplicateCreate);  // [{name: "John", slot: 5}]

    Edit: Explanation

    Original Code:
    For each item in newData, it checks if there’s an item in oldData with the same name but a different slot. This approach leads to false positives, like including {name: "John", slot: 3}, since there’s another "John" in oldData with a different slot.

    Revised Code:
    For each item in newData, it checks two things:

    • If there’s an exact match in `oldData (both name and slot).
    • If there’s a name match in oldData (just the name). The item from newData is included in the result only if there’s a name match but not an exact match. This ensures that only true duplicates (same name, different slot, and no exact match in oldData) are included in the result.
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  2. 0

    Same as jagmitg, failed to convert to single check. But, it will be a bit more optimal in speed due to exiting the calculation on first .some:

      const duplicateCreate = newData.filter((order1) => {
    return oldData.some((order2) => {
      return (
        order1.name === order2.name 
      ) 
    }) && !oldData.some((order2) => {
        return (
        order1.name === order2.name && order1.slot === order2.slot)
    })
  });
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  3. 0

    There’s no need to check all conditions in jagmitg’s solution:

    const oldData = [{name: "John", slot: 2}, {name: "John", slot: 3}, {name: "John", slot: 4}];
const newData = [{name: "Alex", slot: 2}, {name: "John", slot: 3}, {name: "Bob", slot: 4}, {name: "John", slot: 5}];

const duplicateCreate = newData.filter((order1) => {
  const nameMatch = oldData.some(order2 => order1.name === order2.name);
  if(!nameMatch) return;
  return !oldData.some(order2 => order1.name === order2.name && order1.slot === order2.slot);
});

console.log(duplicateCreate);

    And a benchmark:

    enter image description here

    <script benchmark data-count="10000000">

    const oldData = [{name: "John", slot: 2}, {name: "John", slot: 3}, {name: "John", slot: 4}];
    const newData = [{name: "Alex", slot: 2}, {name: "John", slot: 3}, {name: "Bob", slot: 4}, {name: "John", slot: 5}];

// @benchmark jagmitg

newData.filter((order1) => {
  const exactMatch = oldData.some(order2 => order1.name === order2.name && order1.slot === order2.slot);
  const nameMatch = oldData.some(order2 => order1.name === order2.name);
  return nameMatch && !exactMatch;
});


// @benchmark Alexander

newData.filter((order1) => {
  const nameMatch = oldData.some(order2 => order1.name === order2.name);
  if(!nameMatch) return;
  return !oldData.some(order2 => order1.name === order2.name && order1.slot === order2.slot);
});

</script>
<script src="https://cdn.jsdelivr.net/gh/silentmantra/benchmark/loader.js"></script>
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