Modify Diagonal, Lower & Upper Triangular Part of Matrix in R (3 Examples)
This post shows how to change the diagonal, lower, and upper triangular part of a matrix in the R programming language.
The post will contain this information:
Let’s do this.
Creating Exemplifying Data
I use the following data as basement for this R tutorial:
my_mat <- matrix(1:16, ncol = 4) # Create example matrix my_mat # Print example matrix
Table 1 shows the structure of our example data – It contains four lines and four numerical columns.
Example 1: Change Lower Triangular Part of Matrix Using lower.tri() Function
In this example, I’ll demonstrate how to apply the lower.tri function to modify the lower triangular values in a matrix object.
Let’s assume that we want to replace all values in the lower part of our matrix to zero.
Then, we can apply the lower.tri function as shown below:
my_mat_new1 <- my_mat # Duplicate matrix my_mat_new1[lower.tri(my_mat_new1)] <- 0 # Change lower triangular part my_mat_new1 # Print updated matrix
Table 2 reveals the output of the previous R programming code: A new matrix where the entire lower part has been set to zero.
Example 2: Change Upper Triangular Part of Matrix Using upper.tri() Function
Example 2 shows how to apply the upper.tri function to replace the values in the upper triangular matrix.
In this example, we’ll substitute the values in the input matrix by new values:
my_mat_new2 <- my_mat # Duplicate matrix my_mat_new2[upper.tri(my_mat_new2)] <- 101:106 # Change upper triangular part my_mat_new2 # Print updated matrix
Table 3 shows the output of the previous R code: As you can see, we have inserted new values at each position of the upper part in our matrix.
Example 3: Change Diagonal of Matrix Using diag() Function
In Example 3, I’ll explain how to adjust the diagonal values in a matrix using the diag function.
More precisely, the following R code inserts NA values for the entire diagonal:
my_mat_new3 <- my_mat # Duplicate matrix my_mat_new3[diag(my_mat_new3)] <- NA # Change diagonal of matrix my_mat_new3 # Print updated matrix
In Table 4 you can see that we have created another matrix containing missing data in the diagonal by running the previous R programming code.
Video & Further Resources
As you have seen in this tutorial, the lower.tri, upper.tri, and diag functions can be used to modify the entries in a matrix object.
Would you like to learn more about the modification of the diagonal, lower, and upper triangular part of a matrix? Then you could watch the following video which I have published on my YouTube channel. In the video, I’m explaining the R code of this article in a live session.
Please accept YouTube cookies to play this video. By accepting you will be accessing content from YouTube, a service provided by an external third party.
If you accept this notice, your choice will be saved and the page will refresh.
In addition, you may want to read the related R articles on my homepage. I have published several tutorials that are related to the modification of the diagonal, lower, and upper triangular part of a matrix already.
- Generate Matrix with i.i.d. Normal Random Variables
- How to Subtract / Add a Vector from / to Each Row of a Matrix
- Find Index Positions of Non-Zero Values in Matrix
- Apply a Function to Each Element of a Matrix
- Create Random Matrix in R
- R Programming Examples
In this post you have learned how to replace the values in the diagonal, lower, and upper triangular part of a matrix in the R programming language. Let me know in the comments, in case you have further comments and/or questions. Furthermore, please subscribe to my email newsletter to receive regular updates on the newest articles.
Statistics Globe Newsletter