The fillData helper method of Victory Stack fails for certain cases

[Dharmesh-Kota]

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Victory version

37.3.6

Code Sandbox link

No response

Bug report

The fillData function in victory-stack's helper methods incorrectly assumes that the input dataset arrays are already sorted by _x. However, in many cases (such as the one shown below), the data comes in an unsorted order. This causes the function to mismatch x values during its map-reconstruction step, leading to missing or incorrect data in the final output.

This bug becomes especially problematic when the x values are timestamps and not sorted — the function uses index - indexOffset to try and realign the original data, which fails if the dataset is out of order.

Steps to reproduce

1. Pass in a datasets array containing multiple series where each dataset array is not sorted by _x values.
2. Ensure there are multiple unique _x values across datasets.
3. Call fillData(props, datasets) with fillInMissingData: true.

Here’s an example dataset that reproduces the issue:

const datasets = [
  [
    { _x: 808470, _y: 1 },
    { _x: 1102244, _y: 0.42 },
    { _x: 1054475, _y: 0.23 },
  ]
];

Expected behavior

The function should produce a "filled" dataset that:

Retains all original data points (matched by _x)
Inserts synthetic points (y: 0 or null) only for missing x values across datasets
Matches _x values accurately, regardless of order in input dataset

Expected output:
[
  { _x: 808470, _y: 1, ... },
  { _x: 1054475, _y: 0.23, ... },
  { _x: 1102244, _y: 0.42, ... }
]

Actual behavior

Because the dataset is unsorted, the original function tries to access dataset[index - indexOffset], which may point to the wrong item. As a result:

Some actual values are skipped
Wrong data may be returned
Synthetic points may be inserted even when valid data exists

Environment

- Device: Mac
- OS: 15.5 (24F74)
- Node: 22.16.0
- pnpm: 10.11.1

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