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

[Uwe Ligges]

Werner Wernersen wrote:

> 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
> 
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