rformatsignificant-digits

Curious output using formatC with 2 significant digits

I want to format figures with 2 significant digits using formatC. But it has a strange behaviour. Here are the figures:

(x <- data.frame(  cil = c(1.234, 0.444, 0.712, 0.999, 1.999)
                 , ciu = c(1.812, 1.234, 0.999, 1.199, 2.690)
                 )
 )
 
x$ci <- with(x,paste("("
              , formatC(cil, format="g", digits=2, flag="#")
              , "-"
              , formatC(ciu, format="g", digits=2, flag="#")
              ,")"
                      )
              )
x

And here are the results:

      cil   ciu         ci
1     1.234 1.812  ( 1.2 - 1.8 )
2     0.444 1.234 ( 0.44 - 1.2 )
3     0.712 0.999 ( 0.71 - 1.0 )
4     0.999 1.199  ( 1.0 - 1.2 )
5     1.999 2.690  (  2. - 2.7 )

In case 5 I expected 2.0 and not 2.. Is there an explanation for this? Did I something wrong with the definition of the parameters?

New curious behaviour: leading space depending if figure was rounded down or up:

y1 <- 18.96552
y2 <- 17.04545
formatC(y1, format="g", digits=2,flag="#")
[1] "  19."
formatC(y2, format="g", digits=2,flag="#")
"17."

Can be solved with trim (from gdata). But anyway, it is a strange behaviour as the first one, which by the way persists (V4.32).

Solution

  • To illustrate what I was saying in my comment, you can do :

    x$ci<-with(x,paste("(",
                   format(cil,digits=2,nsmall=2),
                   "-",
                   format(ciu,digits=2,nsmall=2),")"))
> x
  case   cil   ciu              ci
1    A 1.234 1.812 ( 1.23 - 1.81 )
2    B 0.444 1.234 ( 0.44 - 1.23 )
3    C 0.712 0.999 ( 0.71 - 1.00 )
4    D 0.999 1.199 ( 1.00 - 1.20 )
5    E 1.999 2.690 ( 2.00 - 2.69 )

    or the following, to suppress the spaces before or after the brackets :

    x$ci<-with(x,paste0("(",
                    format(cil,digits=2,nsmall=2),
                    " - ",
                    format(ciu,digits=2,nsmall=2),")"))
> x
  case   cil   ciu          ci
1    A 1.234 1.812 (1.23 - 1.81)
2    B 0.444 1.234 (0.44 - 1.23)
3    C 0.712 0.999 (0.71 - 1.00)
4    D 0.999 1.199 (1.00 - 1.20)
5    E 1.999 2.690 (2.00 - 2.69)

    NB : you actually can get the same result using function formatC but with format="f" instead of "g".

    UPDATE :

    I guess the fact that 0 is not printed after 2. is just a bug in some R versions (weirder thing : if you try the line with 2.01 instead of 1.999, you'll get "2.0"...).

    To make it work with your line and obtain exactly what you want, just add round function :

    x$ci<-with(x,paste("(",
                    formatC(round(cil,2), format="g", digits=2, flag="#"),
                   "-",
                   formatC(round(ciu,2), format="g", digits=2, flag="#"),")"))

> x
  case   cil   ciu             ci
1    A 1.234 1.812  ( 1.2 - 1.8 )
2    B 0.444 1.234 ( 0.44 - 1.2 )
3    C 0.712 0.999 ( 0.71 - 1.0 )
4    D 0.999 1.199  ( 1.0 - 1.2 )
5    E 1.999 2.690  ( 2.0 - 2.7 )