# How to Write a Loop in R

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This post was last Updated on by Himanshu Tyagi to reflect the accuracy and up-to-date information on the page.

In this R tutorial, we will discuss how to write a Loop. Looping statements are used to iterate the elements present in the given data structure or a given range of numbers. We will discuss for loop in R.

## How to Write a Loop in R

Syntax:

```for (iterator in data/sequence)
{
statements
----------
}```

Data is a data structure like a vector, represents a sequence of numbers, and an iterator is a variable used to iterate the data or sequence.

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And statements are used to execute inside for loop.

Example 1: We will create a sequence of numbers from 1 to 10 and display using for loop.

```for (i in 1:10){
print(i)
}```

Output:

```[1] 1
[1] 2
[1] 3
[1] 4
[1] 5
[1] 6
[1] 7
[1] 8
[1] 9
[1] 10```

We can also perform some operations inside an iteration.

Example 2: Sum all the elements

```sum=0
for (i in 1:10){
sum=sum+i
}
print(sum)```

Output:

`[1] 55`

Example 3: iterate through a vector and list

```#create a vector
vector1=c(1:10)

#iterator through a vector
for (i in vector1){
print(i)
}

#create a list
list1=list("php","c","cpp","java","jsp")

#iterator through a vector
for (i in vector1){
print(i)
}

#iterator through a list
for (i in list1){
print(i)
}
```

Output:

```[1] 1
[1] 2
[1] 3
[1] 4
[1] 5
[1] 6
[1] 7
[1] 8
[1] 9
[1] 10
[1] 1
[1] 2
[1] 3
[1] 4
[1] 5
[1] 6
[1] 7
[1] 8
[1] 9
[1] 10
[1] "php"
[1] "c"
[1] "cpp"
[1] "java"
[1] "jsp"```

We can also specify conditions inside for loop.

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Example:

Iterate elements from 1 to 10, and if the values are more significant than 5, print greater than 5.

```#create a vector
vector1=c(1:10)

#iterator through a vector
for (i in vector1){

#condition greater than 5
if(i<=5){
print(i)}else{
print("greater than 5")
}
}

```

Output:

```[1] 1
[1] 2
[1] 3
[1] 4
[1] 5
[1] "greater than 5"
[1] "greater than 5"
[1] "greater than 5"
[1] "greater than 5"
[1] "greater than 5"```

We can control the looping statements using the break keyword through conditional statements. It will terminate the loop.

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Syntax:

```for (iterator in data/sequence)
{
conditional statements
----------
break
----------
other statements
----------
}```

Example:

In this example, we will iterate 10 elements, and if the element is equal to 5, we will stop the iteration using the break keyword.

```#create a vector
vector1=c(1:10)

#iterator through a vector
for (i in vector1){

#break when element is equal to 5
if(i==5){
break
#display
}
print(i)
}

```

Output:

```[1] 1
[1] 2
[1] 3
[1] 4```

next

We can also control the looping statements using the next keyword through conditional statements. It will terminate the loop at a particular condition and starts looping from the next iterating element.

Syntax:

```for (iterator in data/sequence)
{
conditional statements
----------
next
----------
other statements
----------
}```

Example:

In this example, we will iterate 10 elements, and if the element is equal to 5, we will stop the iteration and continue again using next.

```#create a vector
vector1=c(1:10)

#iterator through a vector
for (i in vector1){

# when element is equal to 5 stop the statement and continue using next
if(i==5){
next
#display
}
print(i)
}

```

Output:

```[1] 1
[1] 2
[1] 3
[1] 4
[1] 6
[1] 7
[1] 8
[1] 9
[1] 10```

### Summary

From this tutorial, we discussed for loop in R along with control statements in a loop.

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