How to save a R model?
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How to save a R model?

How to save a R model?

This recipe helps you save a R model

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Recipe Objective

Once we have trained a model and tested it's performance to be satisfactory, we should save the model. The trained model is lost as soon as we close the session. Additionally, with large dataset, training a model is quite time-consuming since you have to run the algorithm again and again. Hence, it is ideal to train and save the model which can be loaded later to predict the outcome on the new dataset. ​

In this recipe, we will demonstrate how to build and save a Regression Tree model. ​

Decision Tree is a supervised machine learning algorithm which can be used to perform both classification and regression on complex datasets. They are also known as Classification and Regression Trees (CART). Hence, it works for both continuous and categorical variables.

Important basic tree Terminology is as follows: ​

  1. Root node: represents an entire popuplation or dataset which gets divided into two or more pure sets (also known as homogeneuos steps). It always contains a single input variable (x).
  2. Leaf or terminal node: These nodes do not split further and contains the output variable

In this recipe, we will only focus on Regression Trees where the target variable is continuous in nature. The splits in these trees are based on minimising the Residual sum of squares of each groups formed. RSS is calculated by the predicted values is the mean response for the training observations within the jth group. ​

STEP 1: Importing Necessary Libraries

# For data manipulation library(tidyverse) # For Decision Tree algorithm library(rpart) # for plotting the decision Tree install.packages("rpart.plot") library(rpart.plot) # Install readxl R package for reading excel sheets install.packages("readxl") library("readxl")

STEP 2: Loading the Train and Test Dataset

Loading the test and train dataset sepearately. Here Train and test are split in 80/20 proportion respectively.

Dataset description: The company wants to predict the cost they should set for a new variant of the kinds of bags based on the attributes mentioned below using the following variables: ​

  1. Height – The height of the bag
  2. Width – The width of the bag
  3. Length – The length of the bag
  4. Weight – The weight the bag can carry
  5. Weight1 – Weight the bag can carry after expansion
# calling the function read_excel from the readxl library train = read_excel('R_253_df_train_regression.xlsx') test = read_excel('R_253_df_test_regression.xlsx') # gives the number of observations and variables involved with its brief description glimpse(train)
Rows: 127
Columns: 6
$ Cost     242, 290, 340, 363, 430, 450, 500, 390, 450, 500, 475, 500,...
$ Weight   23.2, 24.0, 23.9, 26.3, 26.5, 26.8, 26.8, 27.6, 27.6, 28.5,...
$ Weight1  25.4, 26.3, 26.5, 29.0, 29.0, 29.7, 29.7, 30.0, 30.0, 30.7,...
$ Length   30.0, 31.2, 31.1, 33.5, 34.0, 34.7, 34.5, 35.0, 35.1, 36.2,...
$ Height   11.5200, 12.4800, 12.3778, 12.7300, 12.4440, 13.6024, 14.17...
$ Width    4.0200, 4.3056, 4.6961, 4.4555, 5.1340, 4.9274, 5.2785, 4.6...
# gives the number of observations and variables involved with its brief description glimpse(test)
Rows: 32
Columns: 6
$ Cost     1000.0, 200.0, 300.0, 300.0, 300.0, 430.0, 345.0, 456.0, 51...
$ Weight   41.1, 30.0, 31.7, 32.7, 34.8, 35.5, 36.0, 40.0, 40.0, 40.1,...
$ Weight1  44.0, 32.3, 34.0, 35.0, 37.3, 38.0, 38.5, 42.5, 42.5, 43.0,...
$ Length   46.6, 34.8, 37.8, 38.8, 39.8, 40.5, 41.0, 45.5, 45.5, 45.8,...
$ Height   12.4888, 5.5680, 5.7078, 5.9364, 6.2884, 7.2900, 6.3960, 7....
$ Width    7.5958, 3.3756, 4.1580, 4.3844, 4.0198, 4.5765, 3.9770, 4.3...

STEP 3: Data Preprocessing (Scaling)

This is a pre-modelling step. In this step, the data must be scaled or standardised so that different attributes can be comparable. Standardised data has mean zero and standard deviation one. we do thiis using scale() function.

Note: Scaling is an important pre-modelling step which has to be mandatory

# scaling the independent variables in train dataset train_scaled = scale(train[2:6]) # using cbind() function to add a new column Outcome to the scaled independent values train_scaled = data.frame(cbind(train_scaled, Outcome = train$Cost)) train_scaled %>% head()
Weight		Weight1		Length		Height		Width		Outcome
-0.33379271	-0.3132781	-0.08858827	0.4095324	-0.42466337	242
-0.22300101	-0.1970948	0.04945726	0.6459374	-0.22972408	290
-0.23684997	-0.1712763	0.03795346	0.6207701	0.03681581	340
0.09552513	0.1514550	0.31404453	0.7075012	-0.12740825	363
0.12322305	0.1514550	0.37156350	0.6370722	0.33570907	430
0.16476994	0.2418198	0.45209006	0.9223343	0.19469206	450
# scaling the independent variables in train dataset test_scaled = scale(test[2:6]) # using cbind() function to add a new column Outcome to the scaled independent values test_scaled = data.frame(cbind(test_scaled, Outcome = test$Cost)) test_scaled %>% head()
Weight		Weight1		Length		Height		Width		Outcome
0.72483012	0.72445274	0.69959684	2.15715925	1.87080937	1000
0.07204194	0.08459639	0.09077507	0.03471101	-0.06904068	200
0.17201851	0.17756697	0.24556027	0.07758442	0.29059599	300
0.23082825	0.23225555	0.29715533	0.14769072	0.39466263	300
0.35432872	0.35803927	0.34875040	0.25564092	0.22707121	300
0.39549554	0.39632128	0.38486694	0.56280832	0.48296300	430

STEP 4: Creation of Decision Tree Regressor model using training set

We use rpart() function to fit the model.

Syntax: rpart(formula, data = , method = '')

Where:

  1. Formula of the Decision Trees: Outcome ~. where Outcome is dependent variable and . represents all other independent variables
  2. data = train_scaled
  3. method = 'anova' (to Fit a regression model)
# creation of an object 'model' using rpart function model = rpart(Outcome~., data = train_scaled, method = 'anova')

Using rpart.plot() function to plot the decision tree model

rpart.plot(model)

STEP 5: Saving the model

There are two ways to save and load the model:

  1. using save(), load(): When we use save(), we will have to load it using the same name.
  2. using saveRDS(), loadRDS(): saveRDS() does not save the model name and we have the flexibilty to load the model in any other name. Bur saveRDS() can only save one object at a time as it is lower-level function.

Most people prefer saveRDS() over save() as it is serialise the object.

Syntax: saveRDS(model, file =)

where:

  1. model = model that you want to save
  2. file = path with the file extension .rda
# saving the model saveRDS(model, file = "C:/Users/Divit/Desktop/Internship/R-recipes_Jan/R_160 onwards/Decision Tree_classifier/model.rda") #loading the model model_old = readRDS("C:/Users/Divit/Desktop/Internship/R-recipes_Jan/R_160 onwards/Decision Tree_classifier/model.rda") #checking whether the model has been loaded with different name ls()
'model' 'model_old' 'test' 'test_scaled' 'train' 'train_scaled' 'var_dic_list'  
​

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