A nested for loop is a for loop that is contained within another for loop. This allows you to iterate over two or more dimensions of data.
For example, the following code will print the elements of a matrix:
x <- matrix(1:6, 2, 3)
for (i in 1:nrow(x)) {
for (j in 1:ncol(x)) {
print(x[i, j])
}
}
The outer for loop iterates over the rows of the matrix, and the inner for loop iterates over the columns of the matrix. The code block within the inner for loop is executed for each row of the matrix, and the code block within the outer for loop is executed for each column of the matrix.
Nested for loops can be a powerful tool for iterating over multidimensional data. However, it is important to be careful when using nested for loops, as they can make your code difficult to read and understand. If you find yourself in need of a large number of nested for loops, you may want to break up the loops by using functions.
Note
- The inner for loop must always be indented within the outer for loop.
- The inner for loop will be executed as many times as the outer for loop.
- The code block within the inner for loop will be executed for each iteration of the outer for loop.
