Re: [Rd] 1-based arrays and copying vectors

From: Douglas Bates <>
Date: Mon 20 Jun 2005 - 01:03:43 GMT

On 6/19/05, Rob Lopaka Lee <> wrote:
> I'm interfacing to C code that uses 1-based indexing on arrays -- it
> ignores the zeroth element. Thus, input vectors from R must be moved up
> one, and output arrays must be moved down one.
> What is the best way to deal with this using R internal code?

If the C code can be relied upon to ignore the zero'th element of the array then write a wrapper that gets the array, say int v[], from R and passes &v[-1] to your C code. That has the effect of shifting all the addresses back by one position.  

> My current approach is:
> For an input R vector of length n, allocate a new vector(v) of length n+1
> and copy input into v[1] to v[1+n]. Call with new vector.
> For an output array(a) of length n, allocate a new vector of length n-1
> and copy a[1] to a[n] into v[0] to v[n-1].
> If this is the best approach, is there an idiom for copying vectors?

In C you could use the memcpy function or the Memcpy macro defined in <R_ext/RS.h>. mailing list Received on Mon Jun 20 11:05:05 2005

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