R help - Oct 2007 - Replace values on seq

Hey guys, sorry for the inconvenience (this might be a hundred times
answered question), but I have been searching a while and gave up
about the following:

I have the following, table and data:

table <- seq(255, 0, by=-1)
data  <- c(1,8,...)   <--- doesn't matter what's in here

Which would be the most efficient way to replace each data value, v_i,
by table[v_i + 1] ?
And, maybe more important, why is that more efficient?

I used this, but I think is not the best option:

for (i in 1:length(data)){
	data[i] <- table[data[i]+1]
}

Then used mapply, that seems to work better:

f<-function(x){
   255-x
}

mapply(f, data)

Thanks guys in advance,
Walter

> -----Original Message-----
> From: r-help-bounces at r-project.org 
> [mailto:r-help-bounces at r-project.org] On Behalf Of Walter Alini
> Sent: Tuesday, October 23, 2007 1:18 PM
> To: r-help at r-project.org
> Subject: [R] Replace values on seq
> 
> Hey guys, sorry for the inconvenience (this might be a hundred times
> answered question), but I have been searching a while and gave up
> about the following:
> 
> I have the following, table and data:
> 
> table <- seq(255, 0, by=-1)
> data  <- c(1,8,...)   <--- doesn't matter what's in here
> 
> Which would be the most efficient way to replace each data value, v_i,
> by table[v_i + 1] ?
> And, maybe more important, why is that more efficient?
> 
> I used this, but I think is not the best option:
> 
> for (i in 1:length(data)){
> 	data[i] <- table[data[i]+1]
> }
> 
> Then used mapply, that seems to work better:
> 
> f<-function(x){
>    255-x
> }
> 
> mapply(f, data)
> 
> Thanks guys in advance,
> Walter

How about something like

 data<-table[data+1]

Hope this is helpful,

Dan

Daniel J. Nordlund
Research and Data Analysis
Washington State Department of Social and Health Services
Olympia, WA  98504-5204

Is this what you want to do?
> table <- seq(255, 0, by=-1)
> data <- c(1,8,34,100)
> data <- table[data + 1]
> data
[1] 254 247 221 155


On 10/23/07, Walter Alini <walteralini at gmail.com>
wrote:
> Hey guys, sorry for the inconvenience (this might be a hundred times
> answered question), but I have been searching a while and gave up
> about the following:
>
> I have the following, table and data:
>
> table <- seq(255, 0, by=-1)
> data  <- c(1,8,...)   <--- doesn't matter what's in here
>
> Which would be the most efficient way to replace each data value, v_i,
> by table[v_i + 1] ?
> And, maybe more important, why is that more efficient?
>
> I used this, but I think is not the best option:
>
> for (i in 1:length(data)){
>        data[i] <- table[data[i]+1]
> }
>
> Then used mapply, that seems to work better:
>
> f<-function(x){
>   255-x
> }
>
> mapply(f, data)
>
> Thanks guys in advance,
> Walter
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>

-- 
Jim Holtman
Cincinnati, OH
+1 513 646 9390

What is the problem you are trying to solve?

> Hope this is helpful,
Certainly! Thanks Dan and Jim!

Now, I wonder where I can dig in to realize why this is better. Is C
code for this function better than others? Is C guilty on this?

Maybe I am too newbie.

Thanks again, guys!

Walter

> I will report results then,
OK, its better this way, but no so much.

Before: 99.79 (a) vs 0.21 (b)
Now: 99.77 (a) vs 0.23 (b)

But these results continue to be surprising for me.

Ok. Thanks you guys again, I will continue bothering you sometime.

Walter