[R] Formatting significant digits with trailing zeros

Don MacQueen macq at llnl.gov
Fri Mar 14 23:17:12 CET 2003

I need a function like signif(), but returns the rounded values as 
character strings, formatted with trailing zeros where appropriate. 
If anyone has one, I would sure appreciate a copy.



signif() rounds a number to a specified number of significant digits, 
for example:

>  x <- c(2.503,2.477,0.1204)

>  signif(x[1],3)
[1] 2.5

>  signif(x[2],3)
[1] 2.48

>  signif(x[3],3)
[1] 0.12

All of these are correct, numerically. But, the trailing zeros do not 
display, naturally, because the R functions that format numbers for 
printing have no way of knowing that trailing zeros are desired. 
Pretending I have the function I need, named "fmt.signif", it would 
do this:

>  fmt.signif(x[1],3)
[1] "2.50"

>  fmt.signif(x[2],3)
[1] "2.48"

>  fmt.signif(x[3],3)
[1] "0.120"

>  signif(x,3)
[1] "2.50" "2.48" "0.120"

For now, at least, I'm willing to assume that I never want the 
numbers formatted with exponential notation.
Don MacQueen
Environmental Protection Department
Lawrence Livermore National Laboratory
Livermore, CA, USA

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