[R] Confused by code?

[Peter Alspach]

Tena koe

I think you probably meant:
x[as.logical(z)] <- y[as.logical(z)]

i.e., choosing those elements of × and y where z is 1 (TRUE as logical).  Whereas what you have written:

×[z] <- y[z]

references the 0th (by default indexing starts at 1 so this is empty (see ×[0]) and the first element of × and y (repeatedly).

Hope this helps ....

Peter Alspach

-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On Behalf Of Bazman76
Sent: Monday, 24 September 2012 8:53 a.m.
To: r-help at r-project.org
Subject: [R] Confused by code?

x<-matrix(c(1,0,0,0,1,0,0,0,1),nrow=3)
> y<-matrix(c(0,0,0,1,0,0,1,1,0),nrow=3)
> z<-matrix(c(0,1,0,0,1,0,1,0,0),nrow=3)
> x[z]<-y[z]

The resultant matrix x is all zeros except for the last two diagonal cells which are 1's.
While y is lower triangualr 0's with the remaining cells all ones.

I really don't understand how this deceptively simple looking piece of code is giving that result can someone explain please.
I'm obviously missing something pretty basic so please keep your answer suitably basic.



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