Message-ID: <opr2eej6f01pelvz@smtp.tcd.ie>
Date: 2004-01-26T19:46:44Z
From: Simon Cullen
Subject: conditional assignment
In-Reply-To: <20040126191551.GA14785@pusa.informat.uv.es>
On Mon, 26 Jan 2004 20:15:51 +0100, <uaca at alumni.uv.es> wrote:
> I want to conditionally operate on certain elements of a matrix, let me
> explain it with a simple vector example
>
>
>> z<- c(1, 2, 3)
>> zz <- c(0,0,0)
>> null <- (z > 2) & ( zz <- z)
>> zz
> [1] 1 2 3
>
> why zz is not (0, 0, 3) ?????
<snip>
>
> in the other hand, it curious that null has reasonable values
>
>> null
> [1] FALSE FALSE TRUE
What you have done there is create a boolean vector, null, of the same
length as z (and zz).
For instance:
(z > 2) & (zz <- z)
=(F F T) & (T T T) (as assignment - presumably - returns T)
=(F F T).
What will work is:
z <- c(1, 2, 3)
index <- z>2
zz <- z * index
--
SC
Simon Cullen
Room 3030
Dept. Of Economics
Trinity College Dublin
Ph. (608)3477
Email cullens at tcd.ie