[R] Conditionally incrementing a loop counter: Take 2
Mike Jones
MikeJones at westat.com
Fri Dec 28 00:08:26 CET 2007
Since I didn't want the i to increment in the loop when the condition is not met, then in my example I wanted the loop to actually run 14 times instead of the 10 since I wanted 4 of the iterations to be thrown away, or ignored. I still haven't been able to figure this out. Going the "while" route doesn't seem to work for me either.
nums <- numeric(10)
i <- 1
garbage <- 0
while (i <= 10){
x <- runif(1)
cat("x = ",x,"\n")
if (x < 0.1){
nums[i] <- x
i <- i + 1
}
else{
garbage <- garbage+1
}
cat("i = ",i,"garbage = ",garbage,"\n")
}
-----Original Message-----
From: Peter Dalgaard [mailto:p.dalgaard at biostat.ku.dk]
Sent: Thursday, December 27, 2007 5:36 PM
To: Mike Jones
Cc: r-help at stat.math.ethz.ch
Subject: Re: [R] Conditionally incrementing a loop counter: Take 2
Mike Jones wrote:
> My apologies for not including a working example.
>
> Here it is:
>
> for (i in 1:10){
> cat("initial i = ",i,"\n")
> x <- runif(1)
> if (x > 0.7){
> i <- i-1
> }
> cat("second i = ",i,"\n")
> }
>
> When I ran this i got what follows, so there were four cases where I
> wanted the i not to increment.
>
> initial i = 1
> second i = 1
> initial i = 2
> second i = 1
> initial i = 3
> second i = 3
> initial i = 4
> second i = 3
> initial i = 5
> second i = 4
> initial i = 6
> second i = 6
> initial i = 7
> second i = 7
> initial i = 8
> second i = 7
> initial i = 9
> second i = 9
> initial i = 10
> second i = 10
>
>
Is this the kind of effect you want?
> x <- runif(10)
> cbind(x, 1:10, cumsum(x < .7))
x
[1,] 0.384165631 1 1
[2,] 0.392715845 2 2
[3,] 0.895936431 3 2
[4,] 0.910242185 4 2
[5,] 0.689987301 5 3
[6,] 0.237071326 6 4
[7,] 0.225032680 7 5
[8,] 0.001856286 8 6
[9,] 0.392034868 9 7
[10,] 0.655076045 10 8
If you insist on using a loop, you need to separate the loop control
from the manipulation of i, as in (e.g.)
i <- 0
for (j in 1:10){
i <- i + 1
cat("initial i = ",i,"\n")
x <- runif(1)
if (x > 0.7){
i <- i-1
}
cat("second i = ",i,"\n")
}
>> -----Original Message-----
>> From: Mike Jones
>> Sent: Thursday, December 27, 2007 4:35 PM
>> To: 'r-help at lists.R-project.org'
>> Subject: Conditionally incrementing a loop counter
>>
>> Hi,
>> I am trying a for loop from 1 to 10 by 1. However, if a condition
>> does not get met, I want to "throw away" that iteration. So if my
>> loop is for (i in 1:10) and i is say, 4 and the condition is not met
>> then I don't want i to go up to 5. Is there a way to do that? I
>> can't seem to manually adjust i because from what I understand, R
>> creates 10 long vector and uses that to "loops thru" and I'm not sure
>> how to get at the index of that vector. Any suggestions? Thanks in
>> advance.
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>> Mike Jones
>> Westat
>> 1650 Research Blvd. RE401
>> Rockville, MD 20850
>> Ph: 240.314.2312
>>
>>
>
> [[alternative HTML version deleted]]
>
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>
--
O__ ---- Peter Dalgaard Øster Farimagsgade 5, Entr.B
c/ /'_ --- Dept. of Biostatistics PO Box 2099, 1014 Cph. K
(*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk) FAX: (+45) 35327907
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