Modify Diagonal, Lower & Upper Triangular Part of Matrix in R (3 Examples)
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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.
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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.
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