Re: [R] replace values in a matrix subject to boolean condition

From: Werner Wernersen <pensterfuzzer_at_yahoo.de>
Date: Fri 25 Mar 2005 - 00:27:14 EST
```>> Hi everybody!
>>
>> I am sorry to bother you with a question so simple
```
but
>> I think there might be a better solution: >> I have a matrix of size 360x501 where I want to check
>> the value of each 5th column of each row and replace it (and the 6th,
>> 7th,
>> 8th column) by zero if the value is less than 1000. I have written a
```>> double loop
>> to do that but that requires a lot of time.
>>
>> Is there a faster way to achieve this?
```

>
>
>
> Two ways to interpret your question:
>
> 1) if col5 < 100 replace col5 & col6 & col7 & col8
by 0:
>
> X[X[,5] < 1000, 5:8] <- 0
>
>
> 2) if col5 < 100 replace col5 by 0, if col6 < 100
replace col6 by 0, ...:
>
>
> for(i in 5:8)
> X[X[,i] < 1000, i] <- 0
>
> Uwe Ligges
>
>
>
>
>
```>> Thanks,
>>    Werner
>>
>> ______________________________________________
>> R-help@stat.math.ethz.ch mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide!
>> http://www.R-project.org/posting-guide.html
```

>
>
>
>

Now I did it with
```	for (j in seq(3,length(d[1,]),by=5)) {
d[d[,j]<1000,j:(j+3)] <- c(0,0,0,0)
}
```

which is so much faster than the double loop.

Thanks again,

Werner

R-help@stat.math.ethz.ch mailing list
https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Fri Mar 25 00:34:43 2005

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