export function purchaseIndex(totalItemsSold: number, numberOfCustomers: number): number { 
        if (numberOfCustomers === 0) {
            throw new Error('Number of customers cannot be zero');
        }
        return (totalItemsSold / numberOfCustomers) * 1000;
    }

    export function purchaseRate(productPurchases: number, totalTransactions: number): number;
    export function purchaseRate(productPurchases: number[], totalTransactions: number[]): number[];
    export function purchaseRate(productPurchases: number | number[], totalTransactions: number | number[]): number | number[] {
        if (Array.isArray(productPurchases) && Array.isArray(totalTransactions)) {
            if (productPurchases.length !== totalTransactions.length) throw new Error('Arrays must have the same length');
            return productPurchases.map((pp, i) => purchaseRate(pp, totalTransactions[i]));
        }
    if (typeof productPurchases === 'number' && typeof totalTransactions === 'number') {
        if (totalTransactions === 0) throw new Error('Total transactions cannot be zero');
        return (productPurchases / totalTransactions) * 100;
    }
    throw new Error('Input types must match');
    }

    export function liftValue(jointPurchaseRate: number, productAPurchaseRate: number, productBPurchaseRate: number): number;
    export function liftValue(jointPurchaseRate: number[], productAPurchaseRate: number[], productBPurchaseRate: number[]): number[];
    export function liftValue(jointPurchaseRate: number | number[], productAPurchaseRate: number | number[], productBPurchaseRate: number | number[]): number | number[] {
    if (Array.isArray(jointPurchaseRate) && Array.isArray(productAPurchaseRate) && Array.isArray(productBPurchaseRate)) {
        if (jointPurchaseRate.length !== productAPurchaseRate.length || jointPurchaseRate.length !== productBPurchaseRate.length) throw new Error('Arrays must have the same length');
        return jointPurchaseRate.map((jpr, i) => liftValue(jpr, productAPurchaseRate[i], productBPurchaseRate[i]));
    }
    if (typeof jointPurchaseRate === 'number' && typeof productAPurchaseRate === 'number' && typeof productBPurchaseRate === 'number') {
        const expectedJointRate = productAPurchaseRate * productBPurchaseRate;
        if (expectedJointRate === 0) throw new Error('Expected joint rate cannot be zero');
        return jointPurchaseRate / expectedJointRate;
    }
    throw new Error('Input types must match');
    }

    export function costRatio(cost: number, salePrice: number): number;
    export function costRatio(cost: number[], salePrice: number[]): number[];
    export function costRatio(cost: number | number[], salePrice: number | number[]): number | number[] {
    if (Array.isArray(cost) && Array.isArray(salePrice)) {
        if (cost.length !== salePrice.length) throw new Error('Arrays must have the same length');
        return cost.map((c, i) => costRatio(c, salePrice[i]));
    }
    if (typeof cost === 'number' && typeof salePrice === 'number') {
        if (salePrice === 0) throw new Error('Sale price cannot be zero');
        return cost / salePrice;
    }
    throw new Error('Input types must match');
    }

    export function grossMarginRate(salePrice: number, cost: number): number;
    export function grossMarginRate(salePrice: number[], cost: number[]): number[];
    export function grossMarginRate(salePrice: number | number[], cost: number | number[]): number | number[] {
        if (Array.isArray(salePrice) && Array.isArray(cost)) {
            if (salePrice.length !== cost.length) throw new Error('Arrays must have the same length');
            return salePrice.map((sp, i) => grossMarginRate(sp, cost[i]));
        }
        if (typeof salePrice === 'number' && typeof cost === 'number') {
            if (salePrice === 0) throw new Error('Sale price cannot be zero');
            return (salePrice - cost) / salePrice;
        }
        throw new Error('Input types must match');
    }

    export function averageSpendPerCustomer(totalRevenue: number, numberOfCustomers: number): number;
    export function averageSpendPerCustomer(totalRevenue: number[], numberOfCustomers: number[]): number[];
    export function averageSpendPerCustomer(totalRevenue: number | number[], numberOfCustomers: number | number[]): number | number[] {
        if (Array.isArray(totalRevenue) && Array.isArray(numberOfCustomers)) {
            if (totalRevenue.length !== numberOfCustomers.length) throw new Error('Arrays must have the same length');
            return totalRevenue.map((tr, i) => averageSpendPerCustomer(tr, numberOfCustomers[i]));
        }
        if (typeof totalRevenue === 'number' && typeof numberOfCustomers === 'number') {
            if (numberOfCustomers === 0) throw new Error('Number of customers cannot be zero');
            return totalRevenue / numberOfCustomers;
        }
        throw new Error('Input types must match');
    }