[R] "spreading out" a numeric vector

[Greg Snow]

Levi,

Here is one possible function:

spread <- function(x, mindiff) {
  df <- x[-1] - x[-length(x)]
  i <- 1
  while (any(df < mindiff)) {
    x[c(df < mindiff, FALSE)] <- x[c(df < mindiff, FALSE)] - mindiff/10
    x[c(FALSE, df < mindiff)] <- x[c(FALSE, df < mindiff)] + mindiff/10
    df <- x[-1] - x[-length(x)]
    i <- i + 1
    if (i > 100) {
       break
    }
  }
  x
}

I have tried experimenting with using optim to minimize a function of
the distances between new points and old points penealized for being to
close, but it sometimes gave me some weird results, the above has worked
fairly well for me (the above is based on some of the code inside the
triplot function in the TeachingDemos package).

Hope this helps,

-- 
Gregory (Greg) L. Snow Ph.D.
Statistical Data Center
Intermountain Healthcare
greg.snow at imail.org
(801) 408-8111
 
 

> -----Original Message-----
> From: r-help-bounces at r-project.org 
> [mailto:r-help-bounces at r-project.org] On Behalf Of Levi Waldron
> Sent: Saturday, March 22, 2008 7:03 PM
> To: R-help mailing list
> Subject: [R] "spreading out" a numeric vector
> 
> I am creating a timeline plot, but running into a problem in 
> positions where the values to plot are too close together to 
> print the text without overlap.  The simplest way I can think 
> of to solve this (although there may be other ways?) is to 
> create a new numeric vector whose values are as close as 
> possible to the original vector, but spread out to a given 
> minimum difference.  For example, take the following vector:
> 
> > x <- c(1,2,seq(2.1,2.3,0.1),3,4)
> > x
> [1] 1.0 2.0 2.1 2.2 2.3 3.0 4.0
> >
> 
> However, suppose I don't want to plot any of these points 
> with less than 0.5 between them.  The problem could be solved 
> by a function that behaved something like this:
> 
> > x2 <- spread(x,mindiff=0.5)
> > x2
> [1] 0.5 1.0 1.5 2.0 2.5 3.0 4.0
> 
> Or for a minimum difference of 0.2,
> > x2 <- spread(x,mindiff=0.2)
> > x2
> [1] 1.0 1.8 2.0 2.2 2.4 3.0 4.0
> 
> Thus, if there is a cluster of close values, spreading the 
> values may require changing values which previously weren't 
> too close to their nearest neighbors.
> 
> Then I could use segments() to draw lines from the timeline 
> to where the shifted text is printed, labeling tics on the 
> timeline accurately but keeping the text from overlapping.
> 
> Any ideas on how to program this or how to do it using 
> built-in functions would be greatly appreciated.
> 
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