well i have tested in bash file and it always return the same result

sorry for confusion. I mean the parallel version. belows are my test and the result

func ExamplePartitionByParallel3() {
	partitions := lop.PartitionBy([]int{-2, -1, 0, 1, 2, 3, 4, 5}, func(x int) string {
		if x < 0 {
			return "negative"
		} else if x%2 == 0 {
			return "even"
		}
		return "odd"
	})
	fmt.Println(partitions)
	// Output:
	// [[-2 -1], [0 2 4], [1 3 5]]
}

result

=== RUN   ExamplePartitionByParallel3
--- FAIL: ExamplePartitionByParallel3 (0.00s)
got:
[[5 1 3] [2 4 0] [-2 -1]]
want:
[[-2 -1], [0 2 4], [1 3 5]]

Not only is the iteratee called in parallel, but also the append operation as well.

The correct implementation should be:

1. Map each item to a key, using lop.Map.
2. Loop over the items sequentially, read its computed key, and append the item to the corresponding bucket in the result.

There should be no lock in here.