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Steps in Data Preprocessing: What You Need to Know?

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13th Jun, 2023
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Steps in Data Preprocessing: What You Need to Know?

What is Data Preprocessing?

Data preprocessing is an essential step in data analysis and machine learning projects. It involves transforming raw data into a clean and structured format that is suitable for further analysis and modeling. The goal of data preprocessing is to enhance data quality, remove inconsistencies, handle missing values, and prepare the data for specific analysis techniques or machine learning algorithms.

There are several data preprocessing steps that contribute to improving the accuracy and reliability of the results obtained from subsequent stages. One of the primary steps in data preprocessing is data cleaning. This involves identifying and rectifying errors or inconsistencies in the dataset, such as duplicate records, irrelevant data, or incorrect formatting. Techniques for data cleaning include deduplication, handling missing values, correcting inaccuracies, and addressing outliers.

Data transformation is another crucial aspect of data preprocessing. It involves converting the data into a more suitable form for analysis or modeling. Common data transformation techniques include normalization, which scales the data to a standard range, and encoding categorical variables, which represents categorical data numerically.

The goal of data reduction strategies is to minimize the dimensionality of the dataset while retaining vital information. Principal component analysis (PCA), which finds the most significant variables in the dataset, and feature selection, which picks the most relevant features for the analysis or modeling assignment, are two dimensionality reduction approaches.

Data Preprocessing Tools and Libraries

Numerous tools and libraries are available to facilitate data preprocessing tasks that provide efficient and convenient ways to perform various preprocessing operations. Here are some popular data preprocessing tools and libraries:

Pandas: Pandas is a powerful Python library widely used for data manipulation and preprocessing. It offers convenient data structures and functions to handle missing values, clean data, perform transformations, and more.

NumPy: NumPy is a fundamental library for scientific computing in Python. It provides efficient data structures and functions for numerical operations, such as mathematical transformations and handling arrays.

Scikit-learn: Scikit-learn is a versatile machine-learning library in Python. It includes preprocessing modules for tasks like scaling, encoding categorical variables, and feature selection. It also offers tools for data splitting and cross-validation.

TensorFlow: TensorFlow is a popular library for building and training machine learning models. It provides preprocessing functions for data normalization, encoding, and handling missing values. TensorFlow also offers tools for data augmentation, a technique useful in image and text data preprocessing.

Keras is a high-level deep-learning package based on TensorFlow. It provides simple data preparation methods such as picture scaling, image augmentation, and text tokenization.

WEKA: WEKA is a data preprocessing in data mining and machine learning toolkit with a graphical user interface (GUI) and a suite of data pretreatment methods such as cleaning, normalization, and feature selection.

Apache Spark: Apache Spark is a distributed computing framework that incorporates the machine learning package Spark MLlib. For big datasets, Spark MLlib provides scalable and efficient preparation methods like data cleaning, transformation, and feature extraction.

These tools and libraries greatly simplify and streamline the data preprocessing process, allowing data scientists and analysts to perform tasks more efficiently and effectively.

The mining of data entails converting raw data into useful information that can further analyze and derive critical insights. The raw data you obtain from your source can often be in a cluttered condition that is completely unusable. This data needs to be preprocessed to be analyzed, and the steps for the same are listed below.

Data Cleaning

Data cleaning is the first step of data preprocessing in data mining. Data obtained directly from a source is generally likely to have certain irrelevant rows, incomplete information, or even rogue empty cells.

These elements cause a lot of issues for any data analyst. For instance, the analyst’s platform might fail to recognize the elements and return an error. When you encounter missing data, you can either ignore the rows of data or attempt to fill in the missing values based on a trend or your own assessment. The former is what is generally done.

But a greater problem may arise when you are faced with ‘noisy’ data. To deal with noisy data, which is so cluttered that it cannot be understood by data analysis platforms or any coding platform, many techniques are utilized.

If your data can be sorted, a prevalent method to reduce its noisiness is the ‘binning’ method. In this, the data is divided into bins of equal size. After this, each bin may be replaced by its mean values or boundary values to conduct further analysis. 

Another method is ‘smoothing’ the data by using regression. Regression may be linear or multiple, but the motive is to render the data smooth enough for a trend to be visible. A third approach, another prevalent one, is known as ‘clustering.’

In this data preprocessing method in data mining, surrounding data points are clustered into a single group of data, which is then used for further analysis.

Read: Data Preprocessing in Machine Learning

Data Transformation

The process of data mining generally requires the data to be in a very particular format or syntax. At the very least, the data must be in such a form that it can be analyzed on a data analysis platform and understood. For this purpose, the transformation step of data mining is utilized. There are a few ways in which data may be transformed.

A popular way is normalization. In this approach, every point of data is subtracted from the highest value of data in that field and then divided by the range of data in that field. This reduces the data from arbitrary numbers to a range between -1 and 1.

Attribute selection may also be carried out, in which the data in its current form is converted into a set of simpler attributes by the data analyst. Data discretization is a lesser-used and rather context-specific technique, in which interval levels replace the raw values of a field to make the understanding of the data easier.

In ‘concept hierarchy generation,’ each data point of a particular attribute is converted to a higher hierarchy level. Read more on data transformation in data mining.

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Data Reduction

We live in a world in which trillions of bytes and rows of data are generated every day. The amount of data being generated is increasing by the day, and comparatively, the infrastructure for handling data is not improving at the same rate. Hence, handling large amounts of data can often be extremely difficult, even impossible, for systems and servers alike.

Due to these issues, data analysts frequently use data reduction as part of data preprocessing in data mining. This reduces the amount of data through the following techniques and makes it easier to analyze.

In data cube aggregation, an element is known as a ‘data cube’ is generated with a huge amount of data, and then every layer of the cube is used as per requirement. A cube can be stored in one system or server and then be used by others.

In ‘attribute subset selection,’ only the attributes of immediate importance for analysis are selected and stored in a separate, smaller dataset.

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Numerosity reduction is very similar to the regression step described above. The number of data points is reduced by generating a trend through regression or some other mathematical method.

In ‘dimensionality reducing,’ encoding is used to reduce the volume of data being handled while retrieving all the data.

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It is essential to optimize data mining, considering that data is only going to become more important. These steps of data preprocessing in data mining are bound to be useful for any data analyst.

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Rohit Sharma

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Rohit Sharma is the Program Director for the UpGrad-IIIT Bangalore, PG Diploma Data Analytics Program.

Frequently Asked Questions (FAQs)

1What is data preprocessing?

When a lot of data is available everywhere, improper examination of analyzing data might result in misleading conclusions. Thus, before performing any analysis, the representation and quality of data must come first. Data preprocessing is the process of alteration or removal of data before being utilized for some purpose. This process assures or improves performance, and it is a crucial stage in the data mining process. Data preprocessing is usually the most critical aspect of a machine learning project, particularly in computational biology.

2Why is data preprocessing required?

Data preprocessing is necessary because the real-world data is incomplete in most cases, i.e., some characteristics or values, or both, are absent, or only aggregate information is accessible, is noisy because of mistakes or outliers and, has several inconsistencies due to variations in codes, names, etc. So, if the data lacks attributes or attribute values, has noise or outliers, and contains duplicate or incorrect data, it is considered unclean. Any of these will lower the quality of the results. Thus, data preprocessing is required as it removes inconsistencies, noise, and incompleteness from data, allowing it to be analyzed and used correctly.

3What is the importance of data preprocessing in data mining?

We can find the roots of data preprocessing in data mining. Data preprocessing aims to add absent values, consolidate information, classify data, and smooth trajectories. With data preprocessing, it is possible to remove undesirable information from a dataset. This process lets the user have a dataset that contains more critical data to manipulate later in the mining stage. Using data preprocessing along with data mining helps users in editing datasets to rectify data corruption or human mistakes which is essential in getting accurate quantifiers contained in a Confusion matrix. To improve accuracy, users can combine data files and utilize preprocessing to remove any unwanted noise from the data. More sophisticated approaches, such as principal component analysis and feature selection, use statistical formulae of data preprocessing to analyze large datasets captured by GPS trackers and motion capture devices.

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