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Data Preprocessing and Data Wrangling in Machine Learning

Jagreet Kaur | 04 November 2022


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Introduction to Data Preparation

Deep learning and Machine learning are becoming more and more important in today's ERP (Enterprise Resource Planning). During the process of building the analytical model using Deep Learning or Machine Learning the data set is collected from various sources such as a file, database, sensors, and much more. But, the collected data cannot be used directly for performing the analysis process. Therefore, to solve this problem Data Preparation is done. It includes two techniques; Data Preprocessing and Data Wrangling

Data Preparation Architecture

Data Preparation process is an important part of Data Science. It includes two concepts such as Data Cleaning and Feature Engineering. These two are compulsory for achieving better accuracy and performance in the Machine Learning and Deep Learning projects. Data Preparation for Data Cleaning and Feature Engineering

What is the need of Data Preparation?

For achieving better results from the applied model in Machine Learning and Deep Learning projects the format of the data has to be in a proper manner, this is where term Data Preparation is used. Some specified Machine Learning and Deep Learning model need information in a specified format, for example, Random Forest algorithm does not support null values, therefore to execute random forest algorithm null values has to be managed from the original raw data set. Another aspect of Data Preparation and analysis is that the data set should be formatted in such a way that more than one Machine Learning and Deep Learning algorithms are executed in one data set, and the best out of them is chosen.

What is Data Preprocessing?

It is a technique that is used to convert the raw data into a clean data set. In other words, whenever the data is gathered from different sources it is collected in raw format which is not feasible for the analysis. Therefore, certain steps are executed to convert the data into a small clean data set. This technique is performed before the execution of the Iterative Analysis. The set of steps is known as Data Preprocessing. It includes -
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What are the benefits of Data Preprocessing important?

Preprocessing of Data is necessary because of the presence of unformatted real-world data (Raw Data). Mostly real-world data is composed of -

  • Inaccurate data (missing data) - There are many reasons for missing data such as data is not continuously collected, a mistake in data entry, technical problems with biometrics, and much more, which requires proper Data Preparation.
  • The presence of noisy data (erroneous data and outliers) - The reasons for the existence of noisy data could be a technological problem of gadget that gathers data, a human mistake during data entry and much more.
  • Inconsistent data - The presence of inconsistencies are due to the reasons such that existence of duplication within data, human data entry, containing mistakes in codes or names, i.e., violation of data constraints and much more necessitate Data Preparation and analysis.

What Is Data Wrangling?

Data Wrangling is a technique that is executed at the time of making an interactive model. In other words, it is used to convert the raw data into the format that is convenient for the consumption of data. This technique is also known as Data Munging. This method also follows certain steps such as after extracting the data from different data sources, sorting of data using the certain algorithms are performed, decompose the data into a different structured format and finally store the data into another database.

Why Data Wrangling is necessary?

Data Wrangling is an important aspect of implementing the model. Therefore, data is converted to the proper feasible format before applying any model to it. By performing filtering, grouping, and selecting appropriate data accuracy and performance of the model could be increased. Another concept is that when time-series data has to be handled every algorithm is executed with different aspects. Therefore it is used to convert the time series data into the required format of the applied model. In simple words, the complex data is transformed into a usable format for performing analysis on it.
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What is the benefits of Data Wrangling?

It is used to handle the issue of Data Leakage while implementing Machine Learning and Deep Learning. First of all, we have to understand what Data Leakage is?

Data Leakage in Machine Learning and Deep Learning

Data Leakage is responsible for the cause of an invalid Machine Learning/Deep Learning model due to the over-optimization of the applied model. Data Leakage is the term used when the data from outside, i.e., not part of the training dataset is used for the learning process of the model. This additional learning of information by the applied model will disapprove of the computed estimated performance of the model. For example when we want to use the particular feature for performing Predictive Analysis, but that specific feature is not present at the time of training of dataset then data leakage will be introduced within the model. Data Leakage can be demonstrated in many ways that are given below -
  • The Leakage of data from test dataset to the training data set.
  • Leakage of computed correct prediction to the training dataset.
  • Leakage of future data into the past data.
  • Usage of data outside the scope of the applied algorithm
In general, the leakage of data is observed from two primary sources of Machine Learning/Deep Learning algorithms such as feature attributes (variables) and training data set.

Checking the presence of Data Leakage within the applied model

Data Leakage is observed at the time of usage of complex datasets. They are described below -
  • At the time of dividing the time series dataset into training and test, the dataset is a complex problem.
  • The implementation of sampling in a graphical problem is a complex task.
  • Storage of analog observations in the form of audios and images in separate files having a defined size and timestamp.

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How is Data Preprocessing performed?

Data Preprocessing is carried out to remove the cause of unformatted real-world data which we discussed above. First of all, let's explain how missing data can be handled during Data Preparation. Three different steps can be executed which are given below -
  • Ignoring the missing record - It is the simplest and efficient method for handling the missing data. But, this method should not be performed at the time when the number of missing values is immense or when the pattern of data is related to the unrecognized primary root of the cause of the statement problem.
  • Filling the missing values manually - This is one of the best-chosen methods of Data Preparation process. But there is one limitation that when there are large data set, and missing values are significant then, this approach is not efficient as it becomes a time-consuming task.
  • Filling using computed values - The missing values can also be occupied by computing mean, mode or median of the observed given values. Another method could be the predictive values in Preprocessing of Data is that are computed by using any Machine Learning or Deep Learning tools and algorithms. But one drawback of this approach is that it can generate bias within the data as the calculated values are not accurate concerning the observed values.
Let's move further and discuss how we can deal with noisy data. These are the famous methods that can be followed for  Data Preprocessing and analysis - 
  • Data Binning 
  • Preprocessing in Clustering
  • Machine Learning
  • Removing manually

Data Binning

Data binning, or data bucketing, is a data pre-processing procedure used to reduce the effects of little observation errors. The actual data values which fall into a given small interval, a bin, are replaced by a value representative of that interval, often mean or median. This method is also known as local smoothing. There are two types of binning:

  • Unsupervised Binning: Equal width binning, Equal frequency binning.
  • Supervised Binning: Entropy-based binning

Preprocessing in Clustering

In the approach, the outliers may be detected by grouping similar data in the same group, i.e., in the same cluster.

Machine Learning

A Machine Learning algorithm can be executed for the smoothing of data during Preprocessing . For example, Regression Algorithm can be used for the smoothing of data using a specified linear function.

Removing manually

The noisy data can be deleted manually by the human being, but it is a time-consuming Data Preparation process, so mostly this method is not given priority. To deal with the inconsistent data manually and perform Data Preparation and analysis properly, the data is managed using external references and knowledge engineering tools like the knowledge engineering process. Steps To Perform Data Preprocessing

How is Data Wrangling performed?

Data Wrangling is conducted to minimize the effect of Data Leakage while executing the model. Suppose one considers the complete data set for normalization and standardization. In that case, cross-validation is performed to estimate the model's performance leads to the beginning of data leakage. Another problem is observed in that the test model is also included for feature selection while executing each cross-validation fold, which further generates bias during performance analysis. Data Leakage's effect is minimized by performing Data Preparation during the cross-validation process.

The cross-Validation process includes feature selection, outlier detection and removal, projection methods, scaling of selected features, and more. Another solution for better Data Preparation is dividing the complete dataset into a training data set used to train the model and a validation dataset used to evaluate the applied model's performance and accuracy. The model selection is made by looking at the results of the test data set in the cross-validation process. This conclusion will not always be valid as the sample of the test data set could vary. The performance of different models is evaluated for the particular test dataset. Therefore, while selecting the best model, test error is overfitting. The test error variance is determined by using different samples of the test dataset. Choosing of suitable model happens in this way.

Minimizing Data Leakage in Data Wrangling

What is the difference between Data Preparation and  Data Wrangling?

Data Preprocessing steps are performed before the Wrangling. In this case, data is prepared exactly after receiving the data from the data source. In this initial transformations, Data Cleaning or any aggregation of data is performed. It is executed once. For example, we have data where one attribute has three variables, and we have to convert them into three attributes and delete the special characters from them. The concept of Data Preparation steps performed before applying any iterative model and will be executed once in the project. On the other hand, Wrangling is performed during the iterative analysis and model building. This concept at the time of feature engineering. The conceptual view of the dataset changes as different models are applied to achieve a good analytic model.

For example, we have data containing 30 attributes where two attributes are used to compute another attribute, and that computed feature is used for further analysis. In this way, the data could be changed according to the requirement of the applied model, and Data Preparation can be effective.

Tasks of Data Preparation

Different steps are involved in Data Preprocessing. These steps are described below:

  • Data Cleaning
  • Data Integration
  • Data Transformation
  • Data Reduction

Data Cleaning

This is the first step which is implemented in Preprocessing. In this step, the primary focus is on handling missing data, noisy data, detection, and removal of outliers minimizing duplication, and computed biases within the data.

Data Integration

This process is used when data is gathered from various data sources and data are combined to form consistent data. This consistent data after performing data cleaning is used for Data Preparation and analysis.

Data Transformation

This step is used to convert the raw data into a specified format according to the need of the model. The options for the transformation of data are given below -
  • Normalization - In this method, numerical data is converted into the specified range, i.e., between 0 and one so that scaling of data can be performed.
  • Aggregation - The concept can be derived from the word itself, this method is used to combine the features into one. For example, combining two categories can be used to form a new group.
  • Generalization - In this case, lower level attributes are converted to a higher standard.

Data Reduction

After the transformation and scaling of data duplication, i.e., redundancy within the data is removed and efficiently organize the data during Data Preparation. Different Tasks of Data Preprocessing

Tasks of Data Wrangling

The tasks of Data wrangling are described below -

  • Discovering
  • Structuring
  • Cleaning 
  • Enrichment
  • Validating
  • Publishing


Firstly, data should be understood thoroughly and examine which approach will best suit. For example: if have weather data when we analyze the data it is observed that data is from one area and so primary focus is on determining patterns.


As the data is gathered from different sources, the data will be present in various shapes and sizes. Therefore, there is a need for structuring the data in a proper format.


Cleaning or removing of data should be performed that can degrade the performance of the analysis.


Extract new features or data from the given data set to optimize the performance of the applied model.


This approach is used for improving the quality of data and consistency rules so that transformations that are applied to the data could be verified.


After completing the steps of Data Wrangling, the steps can be documented so that similar steps can be performed for the same kind of data to save time. Different Tasks of Data Wrangling

How Data Wrangling improves Data Analytics?

With the advancement in the technology and generation of data, data is collected from various sources. Therefore, in the Data Preparation process managing data in different formats is necessary. As the simple Data Preparation and analysis methods alone are not feasible for the complex problem statement, it is introduced which simplifies the analysis process of a complex issue. In this way, Data Wrangling is used for improving the analysis process of complex problems during Data Preparation.

What is the difference between Data Wrangling vs ETL?

Wrangling technology is used by business analysts, users engaged in business, and managers. On the other hand, ETL (Extract, Transform, and Load) is employed by IT Professionals. They receive the requirements from business people and then they use ETL tools to deliver the data in a required format. Data Wrangling is used to analyze the data that was gathered from different data sources. It is designed specially to handle diverse and complex data of any scale. But in the case of ETL, it can handle structured data that was originated from different databases or operating systems. The primary task of the Wrangling method is to manage the newly generated data from various sources for the analysis process whereas the goal of ETL is to extract, transform and load the data into the central enterprise Data Warehouse for performing analysis process using business applications. Data Wrangling VS ETL Image Source - blog.appliedinformaticsinc.com

What are the best Data Preprocessing Tools?

  • R: R a framework that consists of various packages that can be used for Data Preprocessing like dplyr etc.
  • Weka: Weka is a software that contains a collection of Machine Learning algorithms for the Data Mining process. It consists of Preprocessing tools that are used before applying Machine Learning algorithms.
  • RapidMiner: RapidMiner is an open-source Predictive Analytics Platform for Data Mining process. It provides efficient tools for performing the exact Data Preprocessing process.
  • Python: Python is a programming language that provides various libraries that are used for Preprocessing.

What are the best Data Wrangling Tools?

  • Tabula: Tabula is a tool that is used to convert the tabular data present in pdf into a structured form of data, i.e., spreadsheet.
  • OpenRefine: OpenRefine is open-source software that provides a friendly Graphical User Interface (GUI) that helps to manipulate the data according to your problem statement and makes Data Preparation process simpler. Therefore, it is highly useful software for the non-data scientist.
  • R: R is an important programming language for the data scientist. It provides various packages like dplyr, tidyr, etc. for performing data manipulation.
  • Data Wrangler: Data Wrangler is a tool that is used to convert real-world data into the structured format. After the conversion, the file can be imported into the required application like Excel, R, etc. Therefore, less time will be spent on formatting data manually.
  • CSVKit: CSVKit is a toolkit that provides the facility of conversion of CSV files into different formats like CSV to JSON, JSON to CSV, and much more. It makes the process of wrangling easy.
  • Python with Pandas: Python is a language with Pandas library. This library helps the data scientist to deal with complex problems efficiently and makes Data Preparation process efficient.
  • Mr. Data Converter: Mr. Data Converter is a tool that takes Excel file as an input and converts the file into required formats. It supports the conversion of HTML, XML, and JSON format.
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Developing a Data Preparation analytic model using Machine Learning and Deep Learning is not an easy task. Data has to be prepared which takes 70 percent of the whole pipeline. Data Preprocessing and Data Wrangling are necessary methods for Data Preparation of data. They are used mostly by Data scientists to improve the performance of the Data Preparation and analysis model. 

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