R has several built-in constants like letters, LETTERS, or month.abb, etc. A constant in a programming language is a value that cannot be changed by the program during its execution.
LETTERS in R
To create a sequential uppercase alphabet in R, use the LETTERS constant. The LETTERS is a character constant in R that generates an uppercase alphabet, and you can use it with different functions to extract the result as per your requirement.
Syntax
LETTERS
Example
print(LETTERS)
Output
[1] "A" "B" "C" "D" "E" "F" "G" "H" "I" "J" "K" "L" "M" "N" "O" "P" "Q" "R" "S"
[20] "T" "U" "V" "W" "X" "Y" "Z"
You can see from the output that it returns uppercase character vectors of the alphabet.
To print specific letters in the sequence, say if you want only J, K & L. use the following code.
LETTERS[10:12]
Output
[1] "J" "K" "L"
Extract characters from LETTERS using head()
To get the first specific part of the object in R, use the head() function. The head() function returns the first part of a vector, matrix, table, data frame, or function.
In this example, we will get the first specific character vectors from LETTERS.
cat("First 10 characters from LETTERS", "\n")
head(LETTERS, 10)
Output
First 10 characters from LETTERS
[1] "A" "B" "C" "D" "E" "F" "G" "H" "I" "J"
And we get the first 10 uppercase letters in the output using the head() function.
Using tail() function
To get the last parts of the object in R, use the tail() function. The tail() function returns the last part of a vector, matrix, table, data frame, or function.
cat("Last 10 characters from LETTERS", "\n")
tail(LETTERS, 10)
Output
Last 10 characters from LETTERS
[1] "Q" "R" "S" "T" "U" "V" "W" "X" "Y" "Z"
Using LETTERS with paste() function
To concat strings in R, use the paste() function. The paste() method converts its input arguments to character strings and concatenates them.
You can create a custom sequence of LETTERS in R using the paste() function. For example, you can create a sequence like,
Millie_A Millie_B Millie_C ... Millie_Z
See the following code.
paste("Millie_", LETTERS, sep = "")
Output
[1] "Millie_A" "Millie_B" "Millie_C" "Millie_D" "Millie_E" "Millie_F"
[7] "Millie_G" "Millie_H" "Millie_I" "Millie_J" "Millie_K" "Millie_L"
[13] "Millie_M" "Millie_N" "Millie_O" "Millie_P" "Millie_Q" "Millie_R"
[19] "Millie_S" "Millie_T" "Millie_U" "Millie_V" "Millie_W" "Millie_X"
[25] "Millie_Y" "Millie_Z"
That is it for LETTERS constant in R.

Krunal Lathiya is an Information Technology Engineer by education and web developer by profession. He has worked with many back-end platforms, including Node.js, PHP, and Python. In addition, Krunal has excellent knowledge of Data Science and Machine Learning, and he is an expert in R Language. Krunal has written many programming blogs, which showcases his vast expertise in this field.