I need a little help with this filter function

Question

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

Andreas Sinz · Answer

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

Andreas Sinz · Answer

``` 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 ```

oday · Answer

hm

oday · Answer

let me try

oday · Answer

my `filters` value would be `mutableListOf `

Andreas Sinz · Answer

`mutableListOf lt YourCarType gt Boolean gt `

oday · Answer

oh

oday · Answer

what is that a type of

oday · Answer

that itself is a lambda

oday · Answer

ok

Andreas Sinz · Answer

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

oday · Answer

yes

Andreas Sinz · Answer

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

kristofdho · Answer

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

kristofdho · Answer

``` 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 ```

oday · Answer

the fold returned nothing to me

oday · Answer

it didn t fail but nothing was returned by the filter

Andreas Sinz · Answer

show me the code you have right now

oday · Answer

oday · Answer

< kristofdho> s one works fine

oday · Answer

see I didnt know you can do that in the if

kristofdho · Answer

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

oday · Answer

hm

oday · Answer

well budget is still used

oday · Answer

Im not sure what you mean

kristofdho · Answer

```var budgetValue = try nf parse budgetValueTV text toString toInt catch e ParseException Timber d Budget was never entered because in offline mode return emptyList ```

kristofdho · Answer

you can use `budgetValue` after that

oday · Answer

and then the actual filtering

kristofdho · Answer

yes

oday · Answer

yea ok that makes sense

Andreas Sinz · Answer

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

oday · Answer

yes he did

oday · Answer

ahhh

oday · Answer

true I did the same error in < kristofdho> s example now and it also returned nothing

oday · Answer

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

oday · Answer

yes they work exactly the same

oday · Answer

im not really sure how < kristofdho> s solution works though

kristofdho · Answer

short circuiting or conditions stuck out tongue

oday · Answer

but < Andreas Sinz> s seems more elegant

oday · Answer

what if I want to add more

oday · Answer

it becomes a monstrosity

Andreas Sinz · Answer

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