Hi:

On Fri, Apr 30, 2010 at 6:08 AM, arnaud Gaboury <arnaud.gaboury@gmail.com>wrote:

> Dear group,
>
> I am losing my mind with a simple question. Sorry if obvious, but I maybe
> start to be confused after days and days of reading documentations.
>
> Df :
>
>
> df <-
> structure(list(a = 1:3, b = 4:6, c = structure(c(1L, 1L, 1L), class =
> "factor", .Label = "w")), .Names = c("a",
> "b", "c"), row.names = c(NA, -3L), class = "data.frame")
>
> I want to multiply first and second by -1.
>
> > x$a<-x$a*-1
> > x$b<-x$b*-1
>

This is a rather dangerous syntax; if you must write it this way, it's
better to
enclose the -1 in parentheses so that the intent is clear. One way is, as
others
have suggested,

x[, 1:2] <- x[, 1:2] * (-1)

For this example, it's just as simple to write

x[, 1:2] <-  -df[, 1:2]

and note that I made sure to space between the assignment and the minus
sign for readability...

HTH,
Dennis

>
> This returns what I want, but there must be an one line command to do it,
> right?
>
> TY for help
>
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