R help - May 2003 - var[i]

Dear all,
How could I use variables in a loop that their names are in a vector? 
For example:

aaa <- 1:10
bbb <- aaa*2
ccc <- aaa+bbb

varn <- c("aaa", "bbb", "ccc")
m <- rep(NA, 3)

for (i in 1:length(varn)) m[i] <- mean(varn[i])  # wrong


thanks in advance

Juli



--
"Wars do not solve problems, wars generate even more problems"

Hi,

If I understand you correctly, then:

On Thu, 1 May 2003, juli g. pausas wrote:
> How could I use variables in a loop that their names are in a vector? 
> For example:
> 
> aaa <- 1:10
> bbb <- aaa*2
> ccc <- aaa+bbb
> 
> varn <- c("aaa", "bbb", "ccc")
Take a look at your varn here.  You'll notice :
> varn
[1] "aaa" "bbb" "ccc"
> m <- rep(NA, 3)
> 
> for (i in 1:length(varn)) m[i] <- mean(varn[i])  # wrong
You can probably do this as a list:
aaa <- 1:10
bbb <- aaa*2
ccc <- aaa+bbb

varn <- list(aaa, bbb, ccc)
m <- rep(NA, 3)

for (i in 1:length(varn)) m[i] <- mean(varn[[i]])  # wrong   

m

-- 
Cheers,

Kevin

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Here's an example:
> x1 <- 1:3
> x2 <- 4:6
> x3 <- 7:9
> xn <- paste("x", 1:3, sep="")
> m <- numeric(3)
> for(i in 1:3) m[i] <- mean(get(xn[i]))
> m
[1] 2 5 8

HTH,
Andy
> -----Original Message-----
> From: juli g. pausas [mailto:juli at ceam.es]
> Sent: Thursday, May 01, 2003 1:03 PM
> To: r-help
> Subject: [R] var[i]
> 
> 
> Dear all,
> How could I use variables in a loop that their names are in a vector? 
> For example:
> 
> aaa <- 1:10
> bbb <- aaa*2
> ccc <- aaa+bbb
> 
> varn <- c("aaa", "bbb", "ccc")
> m <- rep(NA, 3)
> 
> for (i in 1:length(varn)) m[i] <- mean(varn[i])  # wrong
> 
> 
> thanks in advance
> 
> Juli
> 
> 
> 
> --
> "Wars do not solve problems, wars generate even more problems"
> 
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://www.stat.math.ethz.ch/mailman/listinfo/r-help
>

juli g. pausas wrote:
> Dear all,
> How could I use variables in a loop that their names are in a vector? 
> For example:
> 
> aaa <- 1:10
> bbb <- aaa*2
> ccc <- aaa+bbb
> 
> varn <- c("aaa", "bbb", "ccc")
> m <- rep(NA, 3)
> 
> for (i in 1:length(varn)) m[i] <- mean(varn[i])  # wrong
> 
> 

Use ?get.


for (i in 1:length(varn)) m[i]=mean(get(varn[i]))  # right

sundar

"juli g. pausas" <juli at ceam.es> writes:
> Dear all,
> How could I use variables in a loop that their names are in a vector?
> For example:
> 
> aaa <- 1:10
> bbb <- aaa*2
> ccc <- aaa+bbb
> 
> varn <- c("aaa", "bbb", "ccc")
> m <- rep(NA, 3)
> 
> for (i in 1:length(varn)) m[i] <- mean(varn[i])  # wrong
....mean(get(varn[i])).

However, the preferred method might be

sapply(list(aaa,bbb,ccc),var)

or

sapply(data.frame(aaa,bbb,ccc),var)

(which of course only works when the vectors have the same length, and
reminds me that one of the bricks in my road to Hell is to write an
nlist() which supplies element names like data.frame does...)

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