# [R] intervals from cut() as numerics?

Gavin Simpson gavin.simpson at ucl.ac.uk
Sat May 20 14:42:06 CEST 2006

```On Sat, 2006-05-20 at 17:39 +0800, Berwin A Turlach wrote:
> G'day Gavin,
>
> >>>>> "GS" == Gavin Simpson <gavin.simpson at ucl.ac.uk> writes:
>
>     GS> The problem is getting the range/interval for each group from
>     GS> (4,4.3], so I can automate this.
> Most likely there is an easier way, but this seems to work:
>
> ## get the levels of groups:
> > tmp <- levels(groups)
> ## remove the opening "(" and closing "]" from the string:
> > tmp1 <- sapply(tmp, function(x) substr(x, 2, nchar(x)-1))
> ## split into two character strings:
> > tmp2 <- strsplit(tmp1, ",")
> ## turn into results into two numbers:
> > tmp3 <- lapply(tmp2, as.numeric)
>
> ## Of course, we can do everything in one go:
> > lapply(strsplit(sapply(levels(groups), function(x) substr(x, 2, nchar(x)-1)), ","), as.numeric)

Many thanks Berwin. My brain wasn't in character string processing mode,
but your solution works just fine. For the archives then, here is the
full script:

## example data
dat <- seq(4, 7, by = 0.05)
x <- sample(dat, 30)
y <- sample(dat, 30)
## residuals
error <- x - y
## break range of x into 10 groups
groups <- cut(x, breaks = 10)
##calculate bias (mean) per group
max.bias <- aggregate(error, list(group = groups), mean)\$x
## turn cut intervals into numeric
interv <- lapply(strsplit(sapply(levels(groups),
function(x) substr(x, 2,
nchar(x)-1)), ","),
as.numeric)
## reformat cut intervals as 2 col matrix for easy plotting
interv <- matrix(unlist(interv), ncol = 2, byrow = TRUE)
## plot the residuals vs observed
plot(x, error, type = "n")
abline(h = 0, col = "grey")
panel.smooth(x, error)
## add bias indicators per group
arrows(interv[,1], max.bias, interv[,2], max.bias,
length = 0.05, angle = 90, code = 3)

All the best,

G

<snip />
> Cheers,
>
>         Berwin
>
> Berwin A Turlach                      Tel.: +61 (8) 6488 3338 (secr)
> School of Mathematics and Statistics        +61 (8) 6488 3383 (self)
> The University of Western Australia   FAX : +61 (8) 6488 1028
> 35 Stirling Highway
> Crawley WA 6009                e-mail: berwin at maths.uwa.edu.au
> Australia                        http://www.maths.uwa.edu.au/~berwin
>
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