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  • Post category:R Programming
  • Post last modified:July 4, 2024
  • Reading time:11 mins read

How to convert a data frame to a matrix in R? You can use the data.matrix() function to perform this conversion, transforming a data frame into a matrix. In R, data frames are a common way to store tabular data, where each column can contain different types of data (numeric, factor, character, etc.). However, sometimes it is necessary to transform a data frame into a matrix for various numerical computations. The data.matrix() function in R is designed for this purpose.

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In this article, I will explain the data.matrix() function and demonstrate how to convert data frames to matrices using its syntax, parameters, and usage.

Key points-

  • The data.matrix() function converts a data frame to a numeric matrix.
  • This function attempts to convert all columns to numeric types.
  • Factors are replaced by their internal integer codes, and character strings that cannot be converted to numbers will result in NA values.
  • Logical values (TRUE/FALSE) are converted to 1 and 0.
  • NA values in the data frame are preserved in the resulting matrix.
  • The function returns a numeric matrix.
  • The function coerces different column types to numeric mode.
  • It is useful for numerical operations requiring matrix inputs.

R data.matrix() Function

The data.matrix() function converts data frames with various types of columns into matrices. When this function takes a data frame as input, it returns a matrix. If all columns of the data frame are integers, it will return an integer matrix; otherwise, it will return a numeric matrix. If the data frame contains character columns, the function will attempt to coerce all columns to numeric types, which may result in NA values if conversion is not possible.

Syntax of data.matrix() Function

Following is the syntax of the data.matrix() function.


# Synatx of data.matrix() fucntion
data.matrix(df, rownames.force = NA)

Parameters

  • df: A data frame whose elements are logical vectors, factors, or numeric or character vectors.
  • rownames.force: A logical value indicating whether the resulting matrix should have character (rather than NULL) row names. The default value, NA, uses NULL row names if the data frame has ‘automatic’ row names or if it is a zero-row data frame.

Return Value

It generates a matrix by converting all the variables in a data frame to numeric mode and combining them as columns. Factors and ordered factors are substituted with their internal codes.

Convert Numeric Data Frame to Matrix

Let’s create a data frame with numeric columns using a numeric vector and pass it to the data.matrix() function to convert it into a matrix. When this function is applied to a data frame containing all numeric columns, it transforms the data frame into a numeric matrix without changing the values.


# Convert numeric data frame to matrix
df <- data.frame(num = 1:4, squares = c(1, 4, 9, 16))
print("Given data frame:")
print(df)
matrix <- data.matrix(df)
print("After converting data frame to a matrix:")
print(matrix)
print("Get the type")
print(class(matrix))

Yields below output.

r convert data frame to matrix

Factor Data Frame to Matrix in R

To convert a data frame with a factor column to a matrix, you can use the data.matrix() function. This function converts the factor column into its internal integer codes. The resulting matrix contains these integer codes.


# Convert factor data frame to matrix
df <- data.frame(Names = factor(c("Ram", "Varun", "Tej")))
print("Given data frame:")
print(df)

print("Get the type")
print(class(df$Names))

matrix <- data.matrix(df)
print("After converting data frame to a matrix:")
print(matrix)
print("Get the type")
print(class(matrix))

Yields below output.

r convert data frame to matrix

Character Data Frame to Matrix in R

To convert a data frame containing a character column into a matrix, you can use the data.matrix() function. When a data frame with a character column is passed to this function, the characters are coerced into numeric values. This coercion results in NA values since characters cannot be directly converted to numbers. The resulting object is of class matrix.


# Create character data frame to matrix
df <- data.frame(Names = c("Ram", "Varun", "Tej"))
print("Given data frame:")
print(df)

print("Get the type")
print(class(df$Names))
matrix <- data.matrix(df)
print("After converting data frame to a matrix:")
print(matrix)
print("Get the type")
print(class(matrix)) 

Yields below out.


# Output:
[1] "Given data frame:"
   Names
1   Ram
2 Varun
3   Tej

[1] "Get the type"
[1] "character"

[1] "After converting data frame to a matrix:"
      Names
 [1,]     1
 [2,]     3
 [3,]     2

[1] "Get the type"
[1] "matrix" "array" 

Mixed Type Data Frame to Matrix in R

In this example, to convert a data frame with mixed types (numeric and character) into a matrix, use the data.matrix() function. This function transforms the data frame into a matrix where numeric values remain unchanged, while character values are coerced to NA. The resulting object is of class matrix.


# Convert mixed type data frame to matrix
df <- data.frame(id = 1:3,  Names = c("Ram", "Varun", "Tej"))
print("Given data frame:")
print(df)
matrix <- data.matrix(df)
print("After converting data frame to a matrix:")
print(matrix)
print("Get the type")
print(class(matrix))

Yields below output.


# Output:
[1] "Given data frame:"
   id Names
 1  1   Ram
 2  2 Varun
 3  3   Tej

[1] "After converting data frame to a matrix:"
     id Names
[1,]  1     1
[2,]  2     3
[3,]  3     2
[1] "Get the type"
[1] "matrix" "array" 

Use Logical Data Frame

You can also convert a data frame with logical values into a matrix using this function. In the resulting matrix, every logical TRUE value will be represented as 1, and every FALSE value will be represented as 0.


# Convert logical data frame to matrix
df <- data.frame(Logic = c(TRUE, FALSE, TRUE))
print("Given data frame:")
print(df)
print("Get the type")
print(class(df$Logic))
matrix <- data.matrix(df)
print("After converting data frame to a matrix:")
print(matrix)
print("Get the type")
print(class(matrix))

Yields below output.


# Output:
[1] "Given data frame:"
  Logic
1  TRUE
2 FALSE
3  TRUE
[1] "Get the type"
[1] "logical"
[1] "After converting data frame to a matrix:"
     Logic
[1,]     1
[2,]     0
[3,]     1
[1] "Get the type"
[1] "matrix" "array"  

Use Data Frame with NA Values

Finally, you can convert a data frame with NA values into a matrix. If we pass a data frame having NA values into this function it will return the matrix where NA values remain unchanged.


# Convert data frame with NA values to matrix
df = data.frame(a = c(1, NA, 3), b = c(4, 5, NA))
print("Given data frame:")
print(df)
matrix <- data.matrix(df)
print("After converting data frame to a matrix:")
print(matrix)
print("Get the type")
print(class(matrix))

Yields below output.


# Output:
[1] "Given data frame:"
   a  b
1  1  4
2 NA  5
3  3 NA

[1] "After converting data frame to a matrix:"

      a  b
[1,]  1  4
[2,] NA  5
[3,]  3 NA

[1] "Get the type"
[1] "matrix" "array"  

Conclusion

In this article, I explained the data.matrix() function in R is a powerful tool for converting data frames into matrices. This conversion is crucial for numerical computations that require matrix inputs. Understanding the syntax, parameters, and behavior of data.matrix() allows for efficient and accurate data manipulation. Additionally, I covered how to handle the conversion of different types of data frames to matrices, which is particularly useful for data analysis and modeling tasks.

Happy learning!