R round exponential number

Question

I just trying to round in R number like:

> round(1.327076e-09)

I would like it to result in

> 1.33e-09

but results in

> 0

which function can use?

Why should it return `1.32e-09` shouldn't it be `1.33e-09`? Or do you want to just truncate the number after the second dp? — Gavin Simpson, Apr 15 '11 at 11:09

score 20 · Answer 1 · edited Feb 17 '21 at 00:43

20

> signif(1.326135235e-09, digits = 3)
[1] 1.33e-09

edited Feb 17 '21 at 00:43

Tapper

answered Apr 15 '11 at 10:51

Roman Luštrik

James · Answer 2 · 2011-04-15T10:59:22.320

8

Use signif:

x <- 1.327076e-09 
signif(x,3)
[1] 1.33e-09

or sprintf:

sprintf("%.2e",x)
[1] "1.33e-09"

edited Apr 15 '11 at 10:59

answered Apr 15 '11 at 10:52

James

4

Good call with `sprintf`. In general, you only want to lose precision when displaying numbers, not in the actual calculations. `round` and `signif` should be used sparingly. – Richie Cotton Apr 15 '11 at 13:01

Andrie · Answer 3 · 2011-04-15T16:51:31.193

2

The function round will do rounding and you can specify the number of decimals:

x <- 1.327076e-09
round(x, 11)
[1] 1.33e-09

Rising to the challenge set by @Joris and @GavinSimpson - to use trunc on this problem, do the following:

library(plyr)
round_any(x, 1e-11, floor)
[1] 1.32e-09

edited Apr 15 '11 at 16:51

answered Apr 15 '11 at 10:52

Andrie

1

You can add trunc() to do what the OP is doing (not what he's asking). – Joris Meys Apr 15 '11 at 11:19
Ding dong! That's the function that sprung to mind when I saw the desired output, but I figured rounding in OP's questions supersedes the output specified. – Roman Luštrik Apr 15 '11 at 11:24
@Joris but how to get `trunc()` to work here: `> trunc(1.327076e-09) [1] 0`? – Gavin Simpson Apr 15 '11 at 16:41

3 Answers3