R help - Aug 2006 - Integration and Loop in R

Dear All,
I have seldom needed to use loops in R, but now I need to code a loop
with a stride different from one.
In the R manual I downloaded I have the example:
> xc <- split(x, ind)
> yc <- split(y, ind)
> for (i in 1:length(yc)) {
    plot(xc[[i]], yc[[i]]);
    abline(lsfit(xc[[i]], yc[[i]]))
  }
but in my case I'd like to add a condition so that i varies by 4 from
one go to the following one. I cannot figure out the right syntax, can
anyone help here?
Another thing (which could possibly solve my problem): I had a look at
integrate command in R.
It seems to require an object defined as a function to carry out the
integration.
What if I simply have a list of data values? How can I coerce them
into a function recognized by R? Furthermore, are there R routines to
carry out the integration on a non-equally spaced 1D grid?
Best Regards

Lorenzo

On 4 Aug 2006 at 10:23, Lorenzo Isella wrote:

Date sent:      	Fri, 4 Aug 2006 10:23:06 +0200
From:           	"Lorenzo Isella" <lorenzo.isella at gmail.com>
To:             	r-help at stat.math.ethz.ch
Subject:        	[R] Integration and Loop in R
> Dear All,
> I have seldom needed to use loops in R, but now I need to code a loop
> with a stride different from one. In the R manual I downloaded I have
> the example: > xc <- split(x, ind) > yc <- split(y, ind) >
for (i in
> 1:length(yc)) {
>     plot(xc[[i]], yc[[i]]);
>     abline(lsfit(xc[[i]], yc[[i]]))
>   }
> but in my case I'd like to add a condition so that i varies by 4 from
You can make i vary as you wish.
e.g.
steps <- seq(1,40,4)

for (i in steps) ......
> one go to the following one. I cannot figure out the right syntax, can
> anyone help here? Another thing (which could possibly solve my
> problem): I had a look at integrate command in R. It seems to require
> an object defined as a function to carry out the integration. What if
> I simply have a list of data values? How can I coerce them into a
> function recognized by R? Furthermore, are there R routines to carry
> out the integration on a non-equally spaced 1D grid? Best Regards
Try to look at splinefun or approxfun.

HTH
Petr
> 
> Lorenzo
> 
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Petr Pikal
petr.pikal at precheza.cz