Round a double value to x number of decimal places in Swift

In this tutorial, we will see how to round a double value to x number of decimal places in Swift.

Suppose we have a number like 1.34127538359353. Sometimes, we might want to make it shorter, like just 1.34, because we don’t need all those extra digits after the decimal point. Rounding helps us do that, it trims the number to a certain number of decimal places.

Now, follow the methods below to achieve this task.

Using round() function

We can use the round() function to round the double value to a specific number of decimal places. This is a built-in function of Swift.

Example

import Foundation

let value = 1.34127538359353

//Rounds the value of 'value' to two decimal places
let roundedValue = round(100 * value) / 100
print(roundedValue)

In the above code, the 100 * value will multiply the original value by 100. So, the result will be the 134.127538359.

The round(100 * value) will round the result of the multiplication to the nearest integer. It will round 134.127538359 to 134.

Then, I have divided it by 100to round the number to two decimal places.

Output:

1.34

Using String Formatting

We can also use string formatting to round a double value to a specific number of decimal places.

Example

import Foundation

let value = 1.34127538359353

//To round the number to two decimal places and convert it to a string
let roundedValue = String(format: "%.3f", value)
print(roundedValue)

In the above program, the String(format: "%.3f", value) will format the value with three decimal places using the “%.3f” format specifier.

The “f” stands for “floating point” (decimal) number.

Output:

1.341

Using NumberFormatter

Swift provides a built-in class called NumberFormatter , we can use this class to format numbers to a specific number of decimal places.

Example

import Foundation

let value = 1.34127538359353
let formatter = NumberFormatter()
formatter.maximumFractionDigits = 4
if let roundedValue = formatter.string(for: value) {
    print(roundedValue)
}

In the above code, I have applied the NumberFormatter to format numbers.

The maximumFractionDigits property is set to 4 to limit the number of decimal places.

Then, I have used the string(for:) method to convert the double value into a formatted string.

Output:

1.3413

Using  the truncatingRemainder

We can also use the truncatingRemainder(dividingBy:) method to round the double value to a specific number of decimal places.

Example

let value = 1.34127538359353

let roundedValue = (value * 100).truncatingRemainder(dividingBy: 1) == 0 ? 
                   value : (value * 100).rounded() / 100

print(roundedValue)

In the above code, the (value * 100).truncatingRemainder(dividingBy: 1) == 0 will check if there are no decimal places.

If there are no decimal places, it will return the original value. Otherwise, it will round the value to two decimal places.

Output:

1.34