Combine Two DataFrames into One in R

by

Combining DataFrames is a fundamental task in data manipulation and analysis in R programming. Whether you need to merge data from different sources or simply stack datasets, understanding how to effectively combine DataFrames is crucial. This guide will explore three practical examples demonstrating different methods to combine two DataFrames into one, complete with their respective outputs. Before diving into the examples, let’s review the prerequisites necessary for this article.

Prerequisites

To follow along with this guide, you should have:

  • Basic knowledge of R programming
  • R and RStudio installed on your machine
  • Familiarity with DataFrame operations in R

1. Using the rbind() Function

The rbind() function is a straightforward method to combine two DataFrames by stacking them on top of each other (row-wise).

1.1. Example 1: Combining DataFrames by Rows

Code

R
# Create two DataFrames
df1 <- data.frame(Name = c("Alice", "Bob"), Age = c(25, 30))
df2 <- data.frame(Name = c("Charlie", "David"), Age = c(35, 40))

# Combine the DataFrames by rows
combined_df <- rbind(df1, df2)

# Print the combined DataFrame
print(combined_df)

Explanation

  • Creating DataFrames: We create two DataFrames df1 and df2, each with columns Name and Age.
  • Combining DataFrames: The rbind() function combines df1 and df2 by stacking the rows of df2 below the rows of df1.
  • Printing Results: The combined DataFrame is printed to the console.

Output

R
      Name Age
1    Alice  25
2      Bob  30
3  Charlie  35
4    David  40

1.2. Example 2: Handling DataFrames with Different Columns

When DataFrames have different columns, rbind() will not work directly without handling the discrepancies.

Code

R
# Create two DataFrames with different columns
df1 <- data.frame(Name = c("Alice", "Bob"), Age = c(25, 30))
df2 <- data.frame(Name = c("Charlie", "David"), Salary = c(50000, 60000))

# Adjust columns to match
df2$Age <- NA
df1$Salary <- NA

# Combine the DataFrames by rows
combined_df <- rbind(df1, df2)

# Print the combined DataFrame
print(combined_df)

Explanation

  • Creating DataFrames: We create two DataFrames df1 and df2, where df1 has columns Name and Age, and df2 has columns Name and Salary.
  • Adjusting Columns: We add the missing columns (Age in df2 and Salary in df1) with NA values to ensure both DataFrames have the same columns.
  • Combining DataFrames: The rbind() function combines the adjusted DataFrames.
  • Printing Results: The combined DataFrame is printed to the console.

Output

R
      Name Age Salary
1    Alice  25     NA
2      Bob  30     NA
3  Charlie  NA  50000
4    David  NA  60000

2. Using the cbind() Function

The cbind() function is used to combine two DataFrames by placing them side by side (column-wise).

2.1. Example 3: Combining DataFrames by Columns

Code

R
# Create two DataFrames
df1 <- data.frame(Name = c("Alice", "Bob"), Age = c(25, 30))
df2 <- data.frame(Gender = c("F", "M"), Salary = c(50000, 60000))

# Combine the DataFrames by columns
combined_df <- cbind(df1, df2)

# Print the combined DataFrame
print(combined_df)

Explanation

  • Creating DataFrames: We create two DataFrames df1 and df2, where df1 has columns Name and Age, and df2 has columns Gender and Salary.
  • Combining DataFrames: The cbind() function combines df1 and df2 by placing the columns of df2 next to the columns of df1.
  • Printing Results: The combined DataFrame is printed to the console.

Output

R
    Name Age Gender Salary
1  Alice  25      F  50000
2    Bob  30      M  60000

3. Using the merge() Function

The merge() function is used to combine two DataFrames by a common column (key), similar to SQL joins.

2.2. Example 4: Merging DataFrames by a Common Column

Code

R
# Create two DataFrames
df1 <- data.frame(ID = c(1, 2, 3), Name = c("Alice", "Bob", "Charlie"))
df2 <- data.frame(ID = c(2, 3, 4), Age = c(25, 30, 35))

# Merge the DataFrames by the common column 'ID'
merged_df <- merge(df1, df2, by = "ID")

# Print the merged DataFrame
print(merged_df)

Explanation

  • Creating DataFrames: We create two DataFrames df1 and df2, each containing an ID column and additional columns (Name and Age respectively).
  • Merging DataFrames: The merge() function merges df1 and df2 by the common column ID, performing an inner join by default.
  • Printing Results: The merged DataFrame is printed to the console.

Output

R
  ID  Name Age
1  2   Bob  25
2  3 Charlie  30

2.3. Example 5: Outer Merge to Include All Rows

To include all rows from both DataFrames, use an outer merge.

Code

R
# Create two DataFrames
df1 <- data.frame(ID = c(1, 2, 3), Name = c("Alice", "Bob", "Charlie"))
df2 <- data.frame(ID = c(2, 3, 4), Age = c(25, 30, 35))

# Merge the DataFrames by the common column 'ID' with all rows included
merged_df <- merge(df1, df2, by = "ID", all = TRUE)

# Print the merged DataFrame
print(merged_df)

Explanation

  • Creating DataFrames: We create two DataFrames df1 and df2 similar to the previous example.
  • Merging DataFrames: The merge() function merges df1 and df2 by the common column ID, including all rows from both DataFrames with all = TRUE.
  • Printing Results: The merged DataFrame is printed to the console.

Output

R
  ID    Name Age
1  1   Alice  NA
2  2     Bob  25
3  3 Charlie  30
4  4     <NA> 35

Conclusion

In this article, we explored various methods to combine two DataFrames into one in R. We demonstrated how to use the rbind() function to combine DataFrames by rows, how to handle DataFrames with different columns, how to use the cbind() function to combine DataFrames by columns, and how to use the merge() function to merge DataFrames by a common column. Additionally, we showed how to perform an outer merge to include all rows from both DataFrames. Each method offers a unique approach to data combination, catering to different needs in data analysis and manipulation. By mastering these techniques, you can efficiently handle and integrate data in R, enhancing your data processing workflows.