R Data Frames

Introduction

In this chapter, you will learn about data frames in R. Data frames are two-dimensional data structures that can hold elements of different types (numeric, character, logical) in each column. They are similar to tables in a database or Excel spreadsheets and are essential for data manipulation and analysis in R.

Creating Data Frames

Data frames can be created using the data.frame() function, which combines vectors of equal length into a data frame.

Example: Creating a Data Frame

Example:

# Creating a data frame
df <- data.frame(
  Name = c("Alice", "Bob", "Charlie"),
  Age = c(25, 30, 35),
  Gender = c("F", "M", "M")
)
print(df)

Accessing Elements in Data Frames

You can access elements in a data frame using the $ operator, square brackets [], or the subset() function.

Example: Accessing Elements in a Data Frame

Example:

# Accessing columns using the $ operator
print(df$Name)  # Output: "Alice" "Bob" "Charlie"
print(df$Age)  # Output: 25 30 35

# Accessing elements using square brackets
print(df[1, ])  # First row
print(df[, 2])  # Second column
print(df[2, 3])  # Element at second row, third column

# Using subset() function
print(subset(df, Age > 25))

Modifying Elements in Data Frames

You can modify elements in a data frame by specifying the row and column indices or by using the $ operator.

Example: Modifying Elements in a Data Frame

Example:

# Modifying elements
df$Age[2] <- 32
df[3, "Gender"] <- "F"
print(df)

Adding and Removing Columns

You can add columns to a data frame by assigning a new vector to a new column name. You can remove columns by setting them to NULL.

Example: Adding and Removing Columns

Example:

# Adding a column
df$Salary <- c(50000, 55000, 60000)
print(df)

# Removing a column
df$Salary <- NULL
print(df)

Data Frame Operations

Example: Basic Operations

Example:

# Summary statistics
print(summary(df))

# Number of rows and columns
print(nrow(df))  # Output: 3
print(ncol(df))  # Output: 3

# Structure of the data frame
print(str(df))

# Names of the columns
print(names(df))

Merging and Combining Data Frames

You can merge data frames using the merge() function and combine them using the rbind() and cbind() functions.

Example: Merging and Combining Data Frames

Example:

# Creating another data frame
df2 <- data.frame(
  Name = c("Alice", "Bob", "David"),
  Department = c("HR", "Finance", "IT")
)

# Merging data frames by a common column
merged_df <- merge(df, df2, by = "Name")
print(merged_df)

# Combining data frames by rows
combined_df_rows <- rbind(df, df2)
print(combined_df_rows)

# Combining data frames by columns
combined_df_cols <- cbind(df, df2)
print(combined_df_cols)

Example Program Using Data Frames

Here is an example program that demonstrates the use of data frames in R:

# R Program to Demonstrate Data Frames

# Creating a data frame
df <- data.frame(
  Name = c("Alice", "Bob", "Charlie"),
  Age = c(25, 30, 35),
  Gender = c("F", "M", "M")
)
print("Data Frame:")
print(df)

# Accessing elements
print("Name Column:")
print(df$Name)

print("First Row:")
print(df[1, ])

print("Second Column:")
print(df[, 2])

print("Element at (2, 3):")
print(df[2, 3])

# Modifying elements
df$Age[2] <- 32
df[3, "Gender"] <- "F"
print("Modified Data Frame:")
print(df)

# Adding and removing columns
df$Salary <- c(50000, 55000, 60000)
print("Data Frame with Added Column:")
print(df)

df$Salary <- NULL
print("Data Frame with Removed Column:")
print(df)

# Data frame operations
print("Summary of Data Frame:")
print(summary(df))

print("Number of Rows and Columns:")
print(nrow(df))
print(ncol(df))

print("Structure of Data Frame:")
print(str(df))

print("Column Names:")
print(names(df))

# Merging and combining data frames
df2 <- data.frame(
  Name = c("Alice", "Bob", "David"),
  Department = c("HR", "Finance", "IT")
)

merged_df <- merge(df, df2, by = "Name")
print("Merged Data Frame:")
print(merged_df)

combined_df_rows <- rbind(df, df2)
print("Combined Data Frame by Rows:")
print(combined_df_rows)

combined_df_cols <- cbind(df, df2)
print("Combined Data Frame by Columns:")
print(combined_df_cols)

Conclusion

In this chapter, you learned about data frames in R, including how to create, access, modify, and perform operations on data frames. You also learned how to merge and combine data frames. Data frames are essential data structures for data manipulation and analysis in R. By mastering data frames, you can efficiently handle and analyze complex datasets in your R programs.