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# Nested loops in R

We can nest loops, as well as `if` statements, to perform some more complicated tasks. In this recipe, we will first define a square matrix and then write a nested for loop to print only those values where I = J, namely, the values in the matrix placed in (1,1), (2,2), and so on.

## How to do it…

We first define a matrix in R using the following `matrix()` function:

`mat= matrix(1:25, 5,5)`

Now, we use the following code to output only those elements where I = J:

```for (i in 1:5){
for (j in 1:5){
if (i ==j){
print(mat[i,j])
}
}
}```

The `if` statement is nested inside two `for` loop statements. As we have a matrix, we have to use two `for` loops instead of just one. The output of the matrix would be values such as 1, 7, 13, and 19.

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