R help - Jul 2007 - avoiding timconsuming for loop renaming identifiers

Hi All

I was wondering if I can avoid a time-consuming for loop on my 600000 obs
dataset.

school_id   y
8           9.87
8           8.89
8           7.89
8           8.88
20          6.78
20          9.99
20          8.79
31          10.1
31          11

There are, say, 143 different schools in this 600000 obs dataset.

I need to thave sequential identifiers, 1,2,3,4,5,...,143.

I was using an awkward for look that took 30 minutes to run.
sid = 1
dta$sid[1] = 1
for (i in 2:nrow(dta)) {
if (dta$school_id[i] != dta$school_[i-1]) sid = sid+1
dta$sid[i] = sid
}

Any hints appreciated.

Thanks Toby

as.integer(factor(dta[["school_id"]]))

b

On Jul 20, 2007, at 9:26 PM, toby909 at gmail.com wrote:
> Hi All
>
> I was wondering if I can avoid a time-consuming for loop on my  
> 600000 obs dataset.
>
> school_id   y
> 8           9.87
> 8           8.89
> 8           7.89
> 8           8.88
> 20          6.78
> 20          9.99
> 20          8.79
> 31          10.1
> 31          11
>
> There are, say, 143 different schools in this 600000 obs dataset.
>
> I need to thave sequential identifiers, 1,2,3,4,5,...,143.
>
> I was using an awkward for look that took 30 minutes to run.
> sid = 1
> dta$sid[1] = 1
> for (i in 2:nrow(dta)) {
> if (dta$school_id[i] != dta$school_[i-1]) sid = sid+1
> dta$sid[i] = sid
> }
>
> Any hints appreciated.
>
> Thanks Toby
>
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> PLEASE do read the posting guide http://www.R-project.org/posting- 
> guide.html
> and provide commented, minimal, self-contained, reproducible code.

[toby909 at gmail.com]
>I was wondering if I can avoid a time-consuming for loop on my 600000 
>obs dataset.
>school_id   y
>8           9.87
>8           8.89
>8           7.89
>8           8.88
>20          6.78
>20          9.99
>20          8.79
>31          10.1
>31          11
>There are, say, 143 different schools in this 600000 obs dataset.
>I need to thave sequential identifiers, 1,2,3,4,5,...,143.
Hello, Toby.  Maybe:

   dta$id <- cumsum(c(1, diff(dta$school_id) != 0))

-- 
Fran?ois Pinard   http://pinard.progiciels-bpi.ca