React Native: cannot use function as default state hook?

Hi everybody, I have a function that takes a few discounts and groups them by days, so the final result is an array of 7 representing each day with a few discounts or none in each index, for some reason this computation makes the UI don't feel very snappy, only fully completing when I press the UI and showing an uncompleted result UI before that...

I tried placing a function which gives me the resulting array to the default state of my state hook but I gwt the following error:

getVenueDiscounts is not a function

Before this I was using useEffect with empty array to get my array but as I said it didn't feel very snappy...

Here is my method, maybe the problem is I have not optimized my business logic, is it possible to do this calculations better , maybe with a lodash method?

My method for grouping discounts by week days:

const [ weekDiscounts, setWeekDiscounts ] = useState(getVenueDiscounts());

const getVenueDiscounts = () =>
    {
        if(discounts.length == 0)
        {
        var weekDiscountsCopy = [ [], [], [], [], [], [], [] ];
        
        //let weekDiscountsCopy = [...weekDiscounts];
        //let response = await venueStore.getVenueDiscounts({ id:1 });
        console.log(response.data);
        let allDiscounts = _.cloneDeep(venueStore.myDiscounts);
        //let allDiscounts = response.data.discounts;
        //Alert.alert(response.data.discounts.length+' discounts');
        //setDiscounts(discounts);
        console.log(response.data.discounts[0].days);
        for(var i=0; i<response.data.discounts.length;i++)
        {
            let discountDays = allDiscounts[i].days;
            for(var x=0; x<discountDays.length;x++)
            {
                if(discountDays[x].id == 1) 
                {
                    weekDiscountsCopy[0].push(allDiscounts[i]);
                }
                else if(discountDays[x].id == 2) 
                {
                    weekDiscountsCopy[1].push(allDiscounts[i]);
                }
                else if(discountDays[x].id == 3) 
                {
                    weekDiscountsCopy[2].push(allDiscounts[i]);
                }
                else if(discountDays[x].id == 4) 
                {
                    weekDiscountsCopy[3].push(allDiscounts[i]);
                }
                else if(discountDays[x].id == 5) 
                {
                    weekDiscountsCopy[4].push(allDiscounts[i]);
                }
                else if(discountDays[x].id == 6) 
                {
                    weekDiscountsCopy[5].push(allDiscounts[i]);
                }
                else if(discountDays[x].id == 7)
                {
                    weekDiscountsCopy[6].push(allDiscounts[i]);
                }
            }
            //setWeekDiscounts(weekDiscountsCopy);
            setDiscounts(allDiscounts);
            return weekDiscountsCopy;
        }
    }
    };

Thanks in advance!