Welcome back! Before we dive into the specifics of manipulating and transforming your data in R, let's recap what we've covered so far. We started with essential R programming concepts, then moved on to acquiring and preparing data for analysis. Now, it's time to take those clean datasets and learn how to manipulate and transform them effectively to uncover insights.

In this lesson, you will master various data manipulation and transformation techniques using the powerful dplyr library. Specifically, you'll learn how to:

1. Subset Your Data: Extract specific columns and filter rows based on conditions to focus on the most relevant parts of your dataset.
2. Transform Data: Modify existing variables and create new ones to enrich your dataset with additional useful information.
3. Aggregate Data: Summarize and group data to generate meaningful statistics and understand patterns within your dataset.

Here's a step-by-step breakdown of the techniques you'll be practicing:

We'll create a sample data frame to demonstrate various data manipulation techniques.

R
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1# Create a sample data frame
2df <- data.frame(
3  ID = 1:5,
4  Name = c("John", "Jane", "Doe", "Smith", "Emily"),
5  Score = c(85, 90, 88, 77, 95)
6)

Subsetting allows you to focus on specific columns or rows in your dataset. Here, we'll use the dplyr library to select the Name and Score columns.

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1# Subsetting Data: Select Name and Score columns
2selected_data <- dplyr::select(df, Name, Score)
3print("Selected Data")
4print(selected_data)

The select function from dplyr is used to extract specific columns from the data frame. In this case, we are selecting the Name and Score columns.

Syntax of select function:

• select(data_frame, column1, column2, ...)
  • data_frame: The data frame from which you want to select columns.
  • column1, column2, ...: The names of the columns you want to select.

Filtering helps you keep only the rows that meet certain conditions. In this example, we'll filter the rows where the Score is greater than 80.

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1# Filtering Data: Keep rows where Score is greater than 80
2filtered_data <- dplyr::filter(df, Score > 80)
3print("Filtered Data")
4print(filtered_data)

The filter function from dplyr is used to extract rows that meet a specified condition. We are keeping rows where the Score is greater than 80.

Syntax of filter function:

• filter(data_frame, condition)
  • data_frame: The data frame from which you want to filter rows.
  • condition: The condition that the rows must meet to be included in the output.

The mutate function allows you to add new columns or modify existing ones. Here, we'll add a new column indicating the Score increased by 10.

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1# Mutating Data: Add a new column showing Score increased by 10
2mutated_data <- dplyr::mutate(df, ScorePlus10 = Score + 10)
3print("Mutated Data")
4print(mutated_data)

The mutate function from dplyr is used to create new variables or modify existing ones. We are adding a new column ScorePlus10, which is the Score increased by 10.

Syntax of mutate function:

• mutate(data_frame, new_column_name = expression)
  • data_frame: The data frame to which you want to add or modify columns.
  • new_column_name: The name of the new column.
  • expression: The expression used to compute the values of the new column.

Aggregation helps summarize data by categories. We'll calculate the mean Score for each ID.

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1# Aggregating Data: Calculate the mean Score for each ID
2grouped_summary <- df %>% dplyr::group_by(ID) %>% dplyr::summarize(mean_score = mean(Score))
3print("Grouped Summary")
4print(grouped_summary)

Explanation: The group_by function from dplyr creates groups within the data, and the summarize function calculates summary statistics for each group. Here, we are computing the mean Score for each ID.

Syntax of group_by and summarize functions:

• group_by(data_frame, grouping_column)
  • data_frame: The data frame to group.
  • grouping_column: The column by which to group the data.
• summarize(grouped_data_frame, summary_column_name = summary_function(column_to_summarize))
  • grouped_data_frame: The grouped data frame.
  • summary_column_name: The name of the new column containing the summary statistic.
  • summary_function(column_to_summarize): The function and column used to compute the summary statistic (e.g., mean(Score)).

Notes on %>% operator:

• The %>% operator, also known as the pipe operator, is a feature in the magrittr package, which is loaded by default with dplyr.
• It allows for a clear and readable way to write chained operations where the output of one function becomes the input to the next.
• In the example provided, %>% is used to chain group_by(ID) and summarize(mean_score = mean(Score)), effectively creating a pipeline of operations on df.

Being proficient at data manipulation and transformation is crucial for any data scientist. Here’s why:

• Make Your Data Analysis-Ready: Ensure that your data is structured and formatted in a way that facilitates deeper analysis.
• Enhance Data Quality: By filtering out irrelevant information and creating new variables, you can improve the quality and relevance of your data.
• Extract Meaningful Insights: Aggregating and summarizing data helps you uncover patterns and trends, enabling more informed decision-making.

By the end of this lesson, you'll be able to manipulate and transform data confidently, setting the stage for advanced analysis and visualization. Ready to take the next step? Let’s start the practice section and transform our data!