Creating Similarity-Based Recommendation Model

Hello guys! Today, I will be showing you on how to create a similarity-based model that could predict the likelihood that the player will buy the item.

Currently, you need these to produce the model:

• K-Nearest Neighbours Regressors

• A player data that is stored in matrix

• An item data that is stored in matrix

Designing Our Feature Vector

Before we start creating our model, we first need to visualize on how we will design our data to increase the likelihood of players purchasing an item.

-- We're just adding 1 here to add "bias".

local playerDataVector = {
    {
        1,
        numberOfCurrencyAmount,
        numberOfItemsAmount,
        timePlayedInCurrentSession,
        timePlayedInAllSessions,
        currentHealthAmount,
        currentDamageAmount
    }
}

local itemDataVector = {
    {
        costAmount,
        rarityValue,
        durationBetweenFirstServerJoinAndThisItemPurchase,
    }
}

Constructing Our Model

Before we start training our model, we first need to build our model.

local DataPredict = require(DataPredict)

-- For single data point purposes, set the maximumNumberOfIterations to 1 to avoid overfitting. Additionally, the more number of maximumNumberOfIterations you have, the lower the learningRate it should be to avoid "inf" and "nan" issues.

local RecommendationModel = DataPredict.Models.KNearestNeighboursRegressor.new({useWeightedDistance = true, distanceFunction = "CosineDistance"})

Prediction And Training

In here, let’s assume that we have a shop GUI that the player can interact with. Since the prediction and training are closely related in terms of code, I will be splitting the process in different subsections.

Upon Player Opening Shop GUI

The code shown below demonstrate on how to generate the recommendation by the time the player opens the GUI.

local sortedItemToShowArray = {}

local sortedItemToShowSimilarityScoreArray = {}

local sortedItemDataMatrix = {}

local hasPlayerPurchasedTheItemVector -- We will reserve this for now for readability.

local currentPlayerData = getPlayerDataVector()

local function insertItemBasedOnSimilarityScore(itemName, playerItemDataPairVector, itemSimilarityScore)

    if (#itemToShowDictionary == 0) then

        table.insert(itemArray, itemName)

        table.insert(sortedItemToShowSimilarityScoreArray, itemSimilarityScore)

        table.insert(sortedItemDataMatrix, itemDataVector[1])

        return

    end

    for i, sortedItemToShowSimilarityScore in ipairs(sortedItemToShowSimilarityScoreArray)

        if (itemSimilarityScore <= itemToShowSimilarityScore) then continue end

        table.insert(sortedItemToShowArray, i, itemName)

        table.insert(sortedItemToShowSimilarityScoreArray, i, probability)

        table.insert(sortedItemDataMatrix, 1, playerItemDataPairVector[1])

        break

    end

end

for itemName, itemDataVector in pairs(itemDictionary)

    local playerItemDataPairVector = TensorL:concatenate(playerDataVector, itemDataVector, 2)

    local probabilityVector = RecommendationModel:predict(playerItemDataPairVector, true)

    local probabilityValue = probabilityVector[1][1]

    insertItemBasedOnProbability(itemName, playerItemDataPairVector, probability)

end

-- We need this to train our model even if the player does not perform the purchase. Every data counts!

hasPlayerPurchasedTheItemVector = TensorL:createTensor({#itemToShowDictionary, 1}) 

Upon Item Purchase

local function onItemPurchase(itemName)

    local index = table.find(sortedItemToShowArray, itemName)

    if (not index) then return end

    hasPlayerPurchasedTheItemVector[index][1] = 1

end

Upon Player Closing Shop GUI

local function onShopGUIClose()

    local costArray = RecommendationModel:train(sortedItemDataMatrix, hasPlayerPurchasedTheItemVector)

end

This should give you a model that predicts a rough estimate on what they will likely to buy.

Then, you must save the model parameters to Roblox’s DataStores for future use.

local ModelParameters = RecommendationModel:getModelParameters()

Model Parameters Loading

In here, we will use our model parameters so that it can be used to load out models. There are three cases in here:

1. The player is a first-time player.

2. The player is a returning player.

3. Every player uses the same global model.

Case 1: The Player Is A First-Time Player

Under this case, this is a new player that plays the game for the first time. In this case, we do not know how this player would act.

We have a multiple way to handle this issue:

• We create a “global” model that trains from every player, and then make a deep copy of the model parameters and load it into our models.

• We take from other players’ existing model parameters and load it into our models.

Case 2: The Player Is A Returning Player

Under this case, you can continue using the existing model parameters that was saved in Roblox’s Datastores.

RecommendationModel:setModelParameters(ModelParameters)

Case 3: Every Player Uses The Same Global Model

Under this case, the procedure is the same to case 2 except that you need to:

• Load model parameters upon server start.

• Perform auto-save with the optional ability of merging with saved model parameters from other servers.

Conclusion

This tutorial showed you on how to create item recommendation model that allows you to increase the likelihood the player will purchase an item. All you need is some data, some models and a bit of practice to get this right!

That’s all for today and see you later!