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How To Prepare Your Dataset For Machine Learning in Python

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How To Prepare Dataset For Machine Learning in Python. Machine Learning is all about train your model based on current data to predict the future values. So we need the proper amounts to train our model. So in real life, we do not always have the correct data to work with. If the data is not processed correctly, then we need to prepare it and then start training our model. So in this post, we will see step by step to transform our initial data into Training and Test data. For this example, we use python libraries like scikit learn, numpy, and pandas.

Prepare Dataset For Machine Learning in Python

We use the Python programming language to create a perfect dataset. For preparing a dataset, we need to perform the following steps.

#Steps To Prepare The Data.

  1. Get the dataset and import the libraries.
  2. Handle missing data.
  3. Encode categorical data.
  4. Splitting the dataset into the Training set and Test set.
  5. Feature Scaling, if all the columns are not scaled correctly.

So, we will be all the steps on the dataset one by one and prepare the final dataset on which we can apply regression and different algorithms.

#1: Get The Dataset.

Okay, now we are going to use Indian Liver Patient’s data. So we first prepare the complete dataset for this kind of data. I am putting the link here to download the data. Remember, this is not a real dataset, this is just the demo dataset. It looks like the actual dataset. You can get the Real Dataset on this link.

Download File: patientData

Now, we need to create a project directory. So let us build using the following command.

mkdir predata

Now go into the directory.

cd predata

We need to move the CSV file inside this folder.

Now, open the Anaconda Navigator software. If you are new to Anaconda, then please check out this How To Get Started With Machine Learning In Python. After opening Navigator, you can see a screen like below.

How To Prepare Your Dataset For Machine Learning in Python

 

Now, launch the Spyder application and navigate to your project folder. You can see, we have already moved the patientData.csv file so that you can see that file over there.

Okay, now we need to create one Python file called datapre.py and start importing the mathematical libraries.

Write the following code inside datapre.py file. So, your file looks like this. Remember, we are using Python 3

#!/usr/bin/env python3
# -*- coding: utf-8 -*-
"""
Created on Wed Jul 25 18:52:15 2018

@author: your name
"""
import numpy as np
import matplotlib.pyplot as plt
import pandas as pd

Now, select code of three import statements and hit the command + enter and you can see at the right side down, the code is running successfully.

That means, we have successfully imported the libraries. If you found any error then possibly the numpy,  pandas, or matplotlib library is missing. So you need to install that, and that is it.

#2: Handle Missing Data.

In real-time, missing the data happens quite a lot. If you are finding the real-time data set like for the patients, then there is always missing the data. To train the model correctly, we need to fill the data somehow. Otherwise, the model will mispredict the values. Luckily libraries are already available to do that; we need to use the proper function to do that. Now, in our dataset, there is missing data, so we need to fill the data with either mean values or to use some other algorithms. In this example, we are using MEAN to supply the values. So let us do that.

But first, let us divide the dataset into our X and Y axis.

Okay, now write the following code after the importing the libraries.

#!/usr/bin/env python3
# -*- coding: utf-8 -*-
"""
Created on Wed Jul 25 18:52:15 2018

@author: krunal
"""
import numpy as np
import matplotlib.pyplot as plt
import pandas as pd

dataset = pd.read_csv('patientData.csv')

Now, select the following line and hit the command + enter.

dataset = pd.read_csv('patientData.csv')

Okay, so we have included our initial dataset, and you can see here.

Prepare Dataset For Machine Learning

 

Here, you can see that if the value is empty, then nan is displaying. So we need to change it with the MEAN values. So let us do that.

Write the following code.

X = dataset.iloc[:, :-1].values
Y = dataset.iloc[:, 3].values

So, here in the X, we have selected the first four columns and leave the fifth column. It will be our Y.

Remember, indexes are starting from 0. So -1 means last column. So we are selecting the all the columns except the last column.

For Y, we have explicitly selected the fourth column, and the index is 3.

Okay, now we need to handle the missing data. We will use a library Scikit learn.

Write the following code.

...

from sklearn.preprocessing import Imputer
imputer = Imputer(missing_values = 'NaN', strategy = 'mean', axis = 0)
imputer = imputer.fit(X[:, 1:3])
X[:, 1:3] = imputer.transform(X[:, 1:3])

So, here we have to use Imputer module to use the strategy ‘mean’ and fill the missing values with the mean values. Run the above lines and type the X in the Console. You can see something like below. Here, column 1 and 2 have missing values, but we have written 1:3 because the upper bound is excluded that is why we have taken 1 and 3, and it is working fine. Finally, transform the whole column values which have NaN values, and now we have got the filled values.

Machine Learning Dataset Preparation

 

Here, you can see that the mean values of that particular column fill the missing values.

So, we have handled the missing data. Now, head over to the next step.

#3: Encode Categorical data.

In our dataset, there are two categorical columns.

  1. Gender
  2. Liver Disease

So, we need to encode this two columns of data.

# Encode Categorical Data

from sklearn.preprocessing import LabelEncoder, OneHotEncoder
labelencoder_X = LabelEncoder()
X[:, 0] = labelencoder_X.fit_transform(X[:, 0])
onehotencoder = OneHotEncoder(categorical_features = [0])
X = onehotencoder.fit_transform(X).toarray()
labelencoder_Y = LabelEncoder()
Y = labelencoder_Y.fit_transform(Y)

Here, we have encoded the values of the first column. Now, here, we have only two cases for the first column, and that is Female and Male. Now, after transform, the values are 1 for Female, and 0 for Male.

Run the above line and see the changes in categorical data. So, here for Female, it is and Male is 0. It has created one more column and replaces Male and Female according to 1 and 0. That is why it becomes from 3 columns to 4 columns.

Python Machine Learning Dataset Preparation

 

#4: Split the dataset into Training Set and Test Set.

Now, generally, we split the data with the ratio of 70% for the Training Data and 30% to test data. For our example, we split into the 80% for training data and 20% for the test data.

Write the following code inside the Spyder.

# Split the data between the Training Data and Test Data

from sklearn.model_selection import train_test_split
X_train, X_test, Y_train, Y_test = train_test_split(X, Y, test_size = 0.2
                                                    ,random_state = 0)

Run the code, and you can get the four more variables. So, we have the total of seven variables.

Training model in Machine Learning

 

So, here, we have split the both Axis X and Y into X_train and X_test

Y-axis becomes Y_train and Y_test.

So, you have 80% data on the X_train and Y_train and 20% data on the X_test and Y_test.

#5:  Feature Scaling

In a general scenario, machine learning is based on Euclidean Distance. Here for the column Albumin and Age column has an entirely different range of values. So we need to convert those values and make it under the range of values. That is why this is called feature scaling. We need to scale the values for Age column. So let us scale the X_train and X_test.

# Feature Scaling

from sklearn.preprocessing import StandardScaler
sc_X = StandardScaler()
X_train = sc_X.fit_transform(X_train)
X_test = sc_X.transform(X_test)

Here, we do not need for Y because it is already in scaled. Now run the above code and hit the following command.

Feature Scaling in Machine Learning

 

Here, we can see that all the values are appropriately scaled and also you can check the X_test variable as well.

So, we have successfully cleared and prepared the data.

Here, is the final code of our datapre.py.

#!/usr/bin/env python3
# -*- coding: utf-8 -*-
"""
Created on Wed Jul 25 18:52:15 2018

@author: krunal
"""

# Importing Libraries

import numpy as np
import matplotlib.pyplot as plt
import pandas as pd

# Importing Dataset

dataset = pd.read_csv('patientData.csv')
X = dataset.iloc[:, :-1].values
Y = dataset.iloc[:, 3].values

# Handing Missing Dataset

from sklearn.preprocessing import Imputer
imputer = Imputer(missing_values = 'NaN', strategy = 'mean', axis = 0)
imputer = imputer.fit(X[:, 1:3])
X[:, 1:3] = imputer.transform(X[:, 1:3])

# Encode Categorical Data

from sklearn.preprocessing import LabelEncoder, OneHotEncoder
labelencoder_X = LabelEncoder()
X[:, 0] = labelencoder_X.fit_transform(X[:, 0])
onehotencoder = OneHotEncoder(categorical_features = [0])
X = onehotencoder.fit_transform(X).toarray()
labelencoder_Y = LabelEncoder()
Y = labelencoder_Y.fit_transform(Y)

# Split the data between the Training Data and Test Data

from sklearn.model_selection import train_test_split
X_train, X_test, Y_train, Y_test = train_test_split(X, Y, test_size = 0.2
                                                    ,random_state = 0)

# Feature Scaling

from sklearn.preprocessing import StandardScaler
sc_X = StandardScaler()
X_train = sc_X.fit_transform(X_train)
X_test = sc_X.transform(X_test)

So, we have successfully Prepare Dataset For Machine Learning in Python.

Machine Learning has very complex computation. It totally depends on how you get the data and in which condition. Based on the condition of the data, you will start to preprocess the data and split the data into Train and Test model.

Finally, Prepare Dataset For Machine Learning in Python is over. Thanks for taking.

 

2 Comments
  1. Olaitan says

    Why do we have to split dataset before feature scaling

  2. Olaitan says

    Why do we have to split dataset before feature scaling, since we are scaling both train and test set.

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