[R] matrix dimension and for loop
ggrothendieck at yifan.net
Wed Apr 10 18:06:35 CEST 2002
On 10 Apr 2002 at 16:47, Uwe Ligges wrote:
> ggrothendieck at yifan.net wrote:
> > 1. Matrix multiplication. Note that if x is a vector then it is treated as a
> > one column matrix. Also note that NROW(x) is the same as nrow(x), if x is a
> > matrix; however, if x is a vector, then NROW(x) is its length while nrow(x)
> > is NULL. Thus it is important here to use NROW and not nrow. This is
> > discussed in the help on nrow.
> > x %*% diag(y,NROW(x))
> Not quite. The number of *columns* of x, ncol(x), is interesting here,
> not NROW(x),
> or just use length(y) instead of ncol(x) ....
Thanks for pointing out this error. Note, however, that NROW(x) should
be NCOL(x), and not ncol(x), since x can be a vector. length(y) is
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