Data Pre-processing

Shailendra Chauhan  11 min read
24 May 2023

Data Pre-processing


The process of converting unprocessed data into one that is acceptable for analysis is known as data pre-processing. It uses a number of approaches and data preprocessing techniques with the goal of organizing, cleaning, and getting data ready for future analysis. Making sure that the data utilized for analysis is accurate, full, and consistent is the main objective of data pre-processing.

Data pre-processing entails a number of procedures, including data integration, data transformation, and information cleaning. Finding and addressing missing or incorrect data, getting rid of extraneous details, and dealing with duplication are all parts of data cleaning. By normalizing, scaling, or encoding data, data can be transformed into a format that is better suited for analysis. In order to establish a single dataset for analysis, data integration entails merging data from diverse sources.

Due to the frequent occurrence of chaotic, incomplete, or inconsistent raw data, data pre-processing is crucial in data science. These problems can have a significant effect on the precision and efficacy of data analysis, resulting in inaccurate interpretations and unreliable outcomes. The accuracy, consistency, and completeness of the data utilized for analysis can be ensured by pre-processing the data, which enables analysts to derive true insights from the data.

Types of data:

When processing data in data science, a variety of data kinds and data sources are used. The most frequently used types of data in data science are listed below:

  1. Numeric data: Quantitative information that can be measured & processed mathematically, such as height, age, weight, and income, is included in numerical data.
  2. Categorical data: Qualitative information that cannot be quantified mathematically, such as gender, color, and religion, is included in categorical data.
  3. Text data: Unstructured text data includes emails, posted social media posts, and other documents that can be examined using methods of natural language processing.
  4. Time series data: These types of data are compiled over time and include things like stock prices, weather information, and website visitor statistics.
  5. Image data: Visual data that can be analyzed using computer vision algorithms include images, movies, and satellite images.

Types of data sources:

Here are a few types of data sources:

  1. Internal data sources: These include information produced by an organization, such as financial, customer, and sales data.
  2. External data sources: These sources of information come from outside of the organization and may include social media, public datasets, and government information.
  3. Streaming data sources: These sources include continuously produced real-time data, such as data from sensors, feeds from social media, and financial data.
  4. Publicly accessible data sources: These include open data repositories that give free access to datasets for study and analysis, like Kaggle, the UCI Machine Learning Repository, or
  5. Third-party data sources: These sources include data that has been purchased or licensed from independent third parties, including marketing, demographic, and consumer behavior data.

Data cleaning in data science

Finding and fixing flaws, inconsistencies & inaccuracies in a dataset and removing them are all steps in the data science process known as data cleaning. It is essential because the accuracy and dependability of the data have a direct bearing on the conclusions and learnings drawn from data analysis and modeling.

The following are some typical methods and tasks for data cleaning in data science:

  • Managing missing data: Measurement errors or incomplete data collection are just two examples of the many causes of missing data points. Imputation, which replaces the values that are missing with value estimates based on the data already available, deletion of the rows or columns containing the missing data, and the use of special values and indicators to denote missing values are all methods for handling missing data.
  • Eliminating duplicates: When various datasets are merged or when data entry errors occur, duplicates might appear. Each observation is guaranteed to be distinct by locating and eliminating duplicate entries, which prevents the analysis results from being distorted.
  • Data standardization: Problems might arise from inconsistent representations and formatting of the data. Having consistent data and enabling reliable analysis are two benefits of standardizing variables like dates, locations, or names.
  • Managing outliers: Outliers are extreme results that drastically vary from the pattern of the overall data. Models and statistical metrics may be distorted by them. Depending on the analysis's particular context and objectives, outliers may be removed or adjusted.
  • Correcting incorrect or inconsistent values: Data may have mistakes or inconsistencies, which include misspellings, improper data types, or inconsistent values. Cleaning entails locating and fixing these problems to guarantee data integrity.
  • Managing data incompatibilities: It is possible to encounter discrepancies in data types, units of measurement, or variable names when combining or integrating datasets from several sources. In order to maintain compatibility and useful analysis, data cleaning entails resolving these inconsistencies.
  • Managing data validation: Data integrity and accuracy is checked during data validation. It involves activities like confirming numerical categories, cross-referencing data with outside sources, or using logical checks to spot data errors.
  • Feature engineering: Enhancing the representation and prediction ability of the data may also require the creation of new features or the transformation of existing ones. Operations like scaling, encoding variables that are categorical, and producing derived variables fall under this category.
  • Documentation and tracking: It's crucial to keep track of all the procedures taken during the data cleaning process, as well as any decisions that were made regarding the original data. A data science project can benefit from collaboration, transparency, and reproducibility by keeping a record of the cleaning procedure.

Data preprocessing techniques

Data preprocessing techniques in data science include converting unstructured raw data into a clean, organized format that can be used for modeling and analysis. Here are a few typical methods for preparing data:

  • Data Cleaning: In order to handle missing data, get rid of duplicates, fix numbers that aren't consistent, and handle outliers, as was mentioned in the prior response, there are several steps involved.
  • Data Integration: Data integration is the process of compiling information from various sources into one cohesive dataset. Inconsistencies in data formats, units, or variable names may need to be fixed in order to do this.
  • Data transformation: Changing data so that it complies with the underlying presumptions and specifications of an analytic or modeling technique. Scaling, normalization, log transformations, & handling skewed distributions are examples of common transformations.
  • Feature Selection: Determine the features (variables) that are the most pertinent for analysis or modeling. As a result, dimensionality is decreased, redundant or useless features are removed, and model performance and interpretability are enhanced.
  • Feature encoding: The technique of representing categorical data numerically so that algorithms may process them. One-hot encoding, label encoding, and ordinal encoding are a few examples of this.
  • Feature Scaling: Scaling numerical characteristics to a common scale, usually to make sure that various features contribute equally to the analysis or modeling process. Standardization (mean of 0 and standard deviation of 1) & normalization (scaling to a given range, e.g., [0, 1]) are two common scaling strategies.
  • Managing Unbalanced Data: Unbalanced class distributions in the target variable can result in biased models. The data can be balanced using methods like oversampling, undersampling, or utilizing specialized algorithms like SMOTE (Synthetic Minority Over-sampling Technique).
  • Handling Text and Categorical Data: Text tokenization, stemming or lemmatization, the elimination of stop words, and the use of methods like TF-IDF (Term Frequency-Inverse Document Frequency) and word embeddings for text representation are some of the preprocessing techniques for text and categorical data.
  • Handling Time Series Data: Time series data frequently calls for certain preprocessing methods, such as resampling, addressing values that are missing in a time-dependent way, or creating features based on temporal lags and patterns.
  • Partitioning Data: Dividing the dataset into validation, training, and test sets is known as partitioning data. This enables testing and verifying models using hypothetical data to judge their effectiveness and capacity for generalization.

Sampling in data science

Sampling in data science is an essential pre-processing technique because it allows data analysts to engage with a smaller group of data without sacrificing the precision and quality of the study. Additionally, data sampling can aid in reducing the computing complexities of the analysis, improving its effectiveness and speed of execution.

To choose a representative selection of data within a larger dataset during data pre-processing, data sampling is a method. By using data sampling, the quantity of data that must be processed can be decreased while maintaining the accuracy & quality of the analysis.

Data science employs a variety of sampling approaches, including:

  • Random Sampling: Using this strategy, data points are chosen at random from the dataset, giving each one an equal opportunity for selection. When attempting to generate a sample that is representative of the full dataset from a huge dataset, random sampling is helpful.
  • Stratified Sampling: This strategy involves selecting a sample at random from each group after stratifying the dataset into various groups or stratification based on a certain characteristic, such as age or gender. When the dataset is uneven or has an irregular distribution, stratified sampling helps to ensure that the number of samples is accurately representing the complete dataset.
  • Cluster Sampling: Using this strategy, a random sample is chosen from each cluster after the dataset has been divided into numerous clusters depending on a certain criterion, such as geographical region or customer segment. When the dataset is excessively big and it would be impractical to choose a random sample across the complete dataset, cluster sampling can be effective.
  • Systematic Sampling: Using this method, each nth data point within the dataset is chosen, where n is a number that has been predetermined. When the dataset is organized and the data exhibit a distinct pattern, systematic sampling is advantageous.

EDA in Data Science

EDA, or exploratory data analysis is an important information pre-processing approach used in data science to better comprehend the data. EDA's objective is to find patterns, connections, & trends in the data so that they can be used to guide further investigation.

EDA in data science usually entails a number of phases, including:

  • Data Visualisation: To find patterns and relationships in the data, this stage entails developing visualizations of the data, including histograms, scatterplots, and heat maps. A strong technique for finding trends, outliers, and various other inconsistencies in the data is data visualization.
  • Descriptive Statistics: To explain the central tendency and variability of the data, this stage involves producing summary statistics including mean, median, mode, variance, as well as standard deviation. Descriptive statistics are additionally useful to spot anomalies in the data, such as outliers.
  • Data Transformation: This stage consists of scaling, normalizing, and standardizing the data to render it easier to analyze. In order to make it simpler to spot patterns and trends, the transformation of data can help to lessen the influence of outliers as well as other irregularities in the data.
  • Correlation Analysis: To find links between variables, this stage computes correlation coefficients between the variables. Strongly associated variables can be found via correlation analysis, and this information can then be utilized to guide further investigation.
  • Hypothesis Testing: In this step, many data-related hypotheses are put to the test, including whether there is a statistically significant difference between two variables. Statistically significant relationships and trends in the data can be found with the aid of hypothesis testing.

Preparing raw data for analysis by locating and managing mistakes, inconsistencies, missing values, as well as other irregularities is a crucial step in the data analysis process. Techniques for cleaning and pre-processing data entail turning unstructured data into something that can be analyzed. These methods aid in increasing the analysis' precision and dependability, guaranteeing that the findings are reliable and useful. In order to limit the amount of data that needs to be processed while maintaining the accuracy and quality of the analysis, methods of sampling are used in data pre-processing to choose a representative subset of data from a larger set of data. A further essential approach for better understanding the data, spotting patterns and linkages, and supplying information for further research is exploratory data analysis (EDA). Generally speaking, data pre-processing is an important phase in the data analysis process since it helps data analysts to derive reliable and significant insights from the data.

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