R – Formatting Decimal places in R

formattingrr-faqrounding

I have a number, for example 1.128347132904321674821 that I would like to show as only two decimal places when output to screen (or written to a file). How does one do that?

``````x <- 1.128347132904321674821
``````

EDIT:

The use of:

``````options(digits=2)
``````

Has been suggested as a possible answer. Is there a way to specify this within a script for one-time use? When I add it to my script it doesn't seem to do anything different and I'm not interested in a lot of re-typing to format each number (I'm automating a very large report).

Best Solution

Background: Some answers suggested on this page (e.g., `signif`, `options(digits=...)`) do not guarantee that a certain number of decimals are displayed for an arbitrary number. I presume this is a design feature in R whereby good scientific practice involves showing a certain number of digits based on principles of "significant figures". However, in many domains (e.g., APA style, business reports) formatting requirements dictate that a certain number of decimal places are displayed. This is often done for consistency and standardisation purposes rather than being concerned with significant figures.

Solution:

The following code shows exactly two decimal places for the number `x`.

``````format(round(x, 2), nsmall = 2)
``````

For example:

``````format(round(1.20, 2), nsmall = 2)
# [1] "1.20"
format(round(1, 2), nsmall = 2)
# [1] "1.00"
format(round(1.1234, 2), nsmall = 2)
# [1] "1.12"
``````

A more general function is as follows where `x` is the number and `k` is the number of decimals to show. `trimws` removes any leading white space which can be useful if you have a vector of numbers.

``````specify_decimal <- function(x, k) trimws(format(round(x, k), nsmall=k))
``````

E.g.,

``````specify_decimal(1234, 5)
# [1] "1234.00000"
specify_decimal(0.1234, 5)
# [1] "0.12340"
``````