[R] get the values of unique ID

[Roger Peng]

You might want to try working with split().  For example:

df <- data.frame(ID = c(1,1,1,2,2,2), Values = c(40,50,40,60,70,80))

sdf <- split(df, df$ID)
lapply(sdf, function(x) with(x, c(ID[1],mean(Values),sd(Values),Values)))

Since each ID could take different numbers of values (I assume), you'll
still end up with a "ragged array".

-roger
_______________________________
UCLA Department of Statistics
rpeng at stat.ucla.edu
http://www.stat.ucla.edu/~rpeng

On Thu, 27 Mar 2003, Jane Yu wrote:

> Hi, All,
> I wonder anyone can help me find a faster algorithm to
> get the values of unique ID (most ID has 2-3 values,
> varies).
> My data looks like:
> ID Values
> 1 250
> 2 300
> 1 251
> 3 5000
> 4 600
> 10 521
> 3  5500
> I would like output to look like:
> ID, avg(values), stdev(values), value 1,val 2,val3,...
> 
> I used 2 for loops trying to get the values
> for (i in 1:n){
>   value <- NULL
>   for(j in 1:m){
>     if(data[j,1] == uniqueid[i]){
>          value <- c(value, data[j,2])
>           ....
>     }
>   }
> }
> Since both n and m are about 10000, the algorithm is
> really slow.  I believe there is some function out
> there that can do better than this in R. 
> 
> Thanks
> 
> -Jindan
> 
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