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kotlinlang

I need a little help with this filter function <https://pastebin.com/i6V7L5xq>

you could build a list of small filter functions and then `fold` over the list of filters and the car list

```
if(selectedCarModelId != null)
    filters.add { selectedCarModelId == it.model_id }

if(selectedCarSubModelId != null)
    filters.add { selectedCarSubModelId == it.submodel_id }

filters.fold(carList) { cars, filter -&gt; cars.filter(::filter) }
```

my `filters` value would be `mutableListOf({})`?

`mutableListOf&lt;(YourCarType) -&gt; Boolean&gt;()`

it is a list of functions that take your `Car` and returns a `Boolean`

`fold` then just takes the original list of cars and applies every `filter` to your list and returns the filtered list of cars

another option is to have the null checks embedded in the filter condition

```    carListings.filter {
        (selectedCarModelId == null || selectedCarModelId == it.model_id)
        &amp;&amp; (selectedCarSubModelId == null || selectedCarSubModelId == it.submodel_id)
        &amp;&amp; (selectedCarTrimId == null || selectedCarTrimId == it.trim_id)
        &amp;&amp; (fromYearSelected == null || fromYearSelected &lt; it.year)
        &amp;&amp; (toYearSelected == null || toYearSelected &gt; it.year)
        &amp;&amp; it.mileage &lt; mileageValue
        &amp;&amp; it.price &lt; budgetValue
    }```

it didn’t fail, but nothing was returned by the filter

see I didnt know you can do that in the if

you should also reduce the scope of the try block, it's way bigger than it needs to be

```var budgetValue = try {
    nf.parse(budgetValueTV.text.toString()).toInt()
} catch (e: ParseException) {
    Timber.d("Budget was never entered because in offline mode.")
    return emptyList()
}```

you swapped the last two filters. it was `it.price &lt; budgetValue` and now its `budgetValue &lt; it.price`. same for mileage

true, I did the same error in <@U70GMFHEJ>’s example now, and it also returned nothing

so both of these solutions should work, let me just try the fold solution again with the correct conditions

im not really sure how <@U70GMFHEJ>’s solution works though

short circuiting or conditions :stuck_out_tongue:

my solution just decouples the "determine which filters to apply" from the actual filtering, so it should be easier to understand what it does :smile: