[R] Question on the idiom: start <- coef; start[fit$pivot] <- coef

Barnet Wagman wagman at enteract.com
Fri Apr 30 09:36:59 CEST 1999

I wonder if someone could  explain how the following R idiom works (it's
used in

    start <- coef
    start[fit$pivot] <- coef

coef is a vector of coefficients, set by  .Fortran("dqrls", ...).
fit$pivot is a vector of integer indexes (indicating how dqrls permuted
the columns
of x).  If coef has n elements, fit$pivot is a permutation of seq(1,5).

start[fit$pivot] is simple enough, but the assignment performs a futher
that I don't understand.  For example

> pivot <- c(1,3,4,2,5)
> a <- c(100,200,300,400,500)
> b <- a
> b[pivot] <- a
> b
[1] 100 400 200 300 500

I guess there must be a replacement function for [], but I haven't
been able to dig up any documentation on it (and I'm not quite sure
to look in the source code).   I'd like to understand what R does when a
is assigned to another vector in this way.

(and thanks for all the other help I've gotten from member of the list

Barnet Wagman

wagman at enteract.com

1361 N. Hoyne
Chicago, IL 60622

r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
Send "info", "help", or "[un]subscribe"
(in the "body", not the subject !)  To: r-help-request at stat.math.ethz.ch

More information about the R-help mailing list