Hi, is there way to simplify this kotlin statement...

# android

[althaf]

Hi, is there way to simplify this kotlin statement, i don't like it taking multiple iterations

private fun List<PaymentTaxDiscountDetail.PaymentTaxDiscount>.getTotalTaxDiscount(): Double {

    var vatPlusDiscountTotal = sumByDouble {
        if (!it.taxType.startsWith(TaxType.WHT.name)) it.whtAmount else 0.0
    }

    val whtTotal = sumByDouble {
        if (it.taxType.startsWith(TaxType.WHT.name)) it.whtAmount else 0.0
    }
    return vatPlusDiscountTotal - whtTotal
}

[f.babic]

you could use partition to split the original list into two subsets and then sum each

[f.babic]

val (first, second) = partition { !it.startsWith(TaxType.WHT.name) }
val vatPlusDiscountTotal = first.sumByDouble { ... }
val whtTotal = second.sumByDouble {... }

return vatPlusDiscountTotal - whtTotal

Something like this

[f.babic]

it'll only iterate over the lists once to filter them and split into two subsets and then summing is another iteration over each list

but in terms of complexity, both approaches are the same for time, this could/should be a bit better, but it could impact the memory more

[f.babic]

at least it's easier to understand I guess 😄

[althaf]

thank you @f.babic complexity is the same, however i was more into the readable aspect

[zsmb]

You could do it very manually with a for loop to avoid any extra allocations, but outside of that partition is probably the most straightforward and easy to read solution

[althaf]

private fun List<PaymentTaxDiscountDetail.PaymentTaxDiscount>.getTotalTaxDiscount(): Double {
    val (whtAmounts, vatAndDiscounts) = partition { it.taxType.startsWith(TaxType.WHT.name) }
    return vatAndDiscounts.sumByDouble { it.whtAmount } - whtAmounts.sumByDouble { it.whtAmount }
}

[f.babic]

look at @zsmb optimizing the heck out of it! 😄

[f.babic]

no extra space or time complexity, single loop

[zsmb]

On second look, I think you could do

private fun List<PaymentTaxDiscountDetail.PaymentTaxDiscount>.getTotalTaxDiscount2(): Double {
    return sumOf {
        if (!it.taxType.startsWith(TaxType.WHT.name)) it.whtAmount else -it.whtAmount
    }
}

This adds to the sum if the tax type is not WHT and subtracts from it otherwise

[althaf]

@zsmb bravo 🙂 i never thought this way, out box the box actually 🙂