Support for fee/commission as % when backtesting

[ibyter]

Describe the solution you'd like
Add a commission/fee as % when performing backtesting.

Almost all brokers charge a percentage fee on each executed trade which should be taken into account when calculating outcome

[cinar]

Thank you for the future request. Let me see if I can add this quickly.

[kfimchenko]

Thank you for the future request. Let me see if I can add this quickly.

Hi! Any ideas? Or maybe there is another way to simulate a broker's commission? I have just backtested the same basic strategies and received like over 9000 percent profit, which makes no sense without a commission.

[ibyter]

@kfimchenko for your reference, the way I worked around it to add the fee rate, is by modifying the module cache one my local filesystem e.g. here in Mac ~/go/pkg/mod/github.com/cinar/indicator/v2@v2.1.9/strategy/outcome.go, and the calculation is done as follows:

package strategy

import "github.com/cinar/indicator/v2/helper"

func Outcome[T helper.Number](values <-chan T, actions <-chan Action) <-chan float64 {
        totalBudget := 1000000.0 // Total funds available for trading
        balance := totalBudget
        shares := 0.0
        totalInvested := 0.0 // Total amount invested in buy actions
        feeRate := 0.002
        sharesPerBuy := 1.0 // Fixed number of shares to buy per Buy action

        return helper.Operate(values, actions, func(value T, action Action) float64 {
                switch action {
                case Buy:
                        // Calculate the total cost for the shares
                        totalCost := sharesPerBuy * float64(value)
                        // Calculate the fee based on the total cost
                        fee := totalCost * feeRate
                        // Total cost including the fee
                        totalCostIncludingFee := totalCost + fee

                        // Check if there's enough balance to cover the total cost including the fee
                        if balance >= totalCostIncludingFee {
                                shares += sharesPerBuy
                                balance -= totalCostIncludingFee
                                totalInvested += totalCostIncludingFee
                        }
                        // If not enough balance, ignore the Buy action

                case Sell:
                        if shares > 0 {
                                // Calculate the proceeds from selling the shares
                                proceeds := shares * float64(value)
                                // Calculate the fee based on the proceeds
                                fee := proceeds * feeRate
                                // Net proceeds after deducting the fee
                                netProceeds := proceeds - fee
                                balance += netProceeds
                                shares = 0
                        }
                        // No action needed for Hold or other actions
                }

                // Corrected Net Gain Calculation
                netGain := (balance + (shares * float64(value))) - totalBudget
                if totalInvested > 0 {
                        roiFraction := netGain / totalInvested
                        return roiFraction
                } else {
                        return 0.0 // Or handle as appropriate when no investment has been made
                }
        })
}

Moreover, this version also handles consecutive buy actions, which is not present in the original library.

I know it's hacky, but it works.