If you create an object like a matrix but forget to name its rows and columns, the rownames() and colnames() functions in R will help you. In this article, we will give you instructions to use the rownames() and colnames() functions to name rows and columns of a matrix-like object. Now, let’s move on.
What are the rownames() and colnames() functions in R?
The rownames() function
The rownames() function gives names for rows to an object like a matrix or a group of vectors.
Syntax:
rownames(object, do.NULL, prefix)
rownames(object) = name
Parameters:
- object: The object that needs to be named rows.
- do.NULL: The initial name of rows. The default value is TRUE.
- prefix: Prefix the name of the rows if the do.NULL is FALSE.
- name: The vector or list or array of names.
The colnames() function
The colnames() function gives names for columns to an object like a matrix or a group of vectors.
Syntax:
colnames(object, do.NULL, prefix)
colnames(object) = name
Parameters:
- object: The object that needs to be named columns.
- do.NULL: The initial name of columns. The default value is TRUE.
- prefix: Prefix the name of the columns if the do.NULL is FALSE.
- name: The vector or list or array of names.
How to use the rownames() and colnames() functions?
Name the rows and columns of a matrix
To warm up, we will learn how to name rows and columns of a matrix. In the example below, we will create two vectors to store elements of the matrix and create a matrix having a size 4×4 from the vectors. Then, we use the rownames() and colnames() functions to name the matrix’s rows and columns.
Code:
# Create two vectors containing values for the matrix
vector1 = c(4, 5, 7, 2, 8, 9, 12, 22)
vector2 = c(1, 0, 11, 6, 3, 15, 21, 13)
# Create a 4x4 matrix from two vectors
matrix = matrix(c(vector1, vector2), nrow=4, ncol = 4)
# Name rows of the matrix
rownames(matrix) = c("row1", "row2", "row3", "row4")
# Name columns of the matrix
colnames(matrix) = c("col1", "col2", "col3", "col4")
cat("The matrix after naming rows and columns:\n")
print(matrix)Result:
The matrix after naming rows and columns:
col1 col2 col3 col4
row1 4 8 1 3
row2 5 9 0 15
row3 7 12 11 21
row4 2 22 6 13
Name the rows and columns of a data frame
The rownames() and colnames() functions can be used to name or rename rows and columns of a data frame. Look at the following example to see more details.
Code:
# Create vectors containing values for the data frame
vector1 = c("John", "David", "Mary", "Thomas", "Susan", "Emily")
vector2 = c(22, 17, 41, 35, 18, 38)
vector3 = c("Male", "Male", "Female", "Male", "Female", "Female")
# Create a data frame from three vectors
df = data.frame(vector1, vector2, vector3)
# Name rows of the data frame
rownames(df) = c("row1", "row2", "row3", "row4", "row5", "row6")
# Name columns of the data frame
colnames(df) = c("Name", "Age", "Gender")
cat("The data frame after naming rows and columns:\n")
print(df)Result:
The data frame after naming rows and columns:
Name Age Gender
row1 John 22 Male
row2 David 17 Male
row3 Mary 41 Female
row4 Thomas 35 Male
row5 Susan 18 Female
row6 Emily 38 Female
Summary
In summary, the rownames() and colnames() functions set names for rows and columns of objects such as matrices, data frames, etc. If the objects’ rows and columns have the initial names, we can use the function to rename them.
Maybe you are interested:
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- diff function in R: Calculate the difference of elements
My name is Robert Collier. I graduated in IT at HUST university. My interest is learning programming languages; my strengths are Python, C, C++, and Machine Learning/Deep Learning/NLP. I will share all the knowledge I have through my articles. Hope you like them.
Name of the university: HUST
Major: IT
Programming Languages: Python, C, C++, Machine Learning/Deep Learning/NLP