help with rle command

Question

I'm having some trouble with an rle command that is designed to find the point at which participants reach 8 contiguous ones in a row.

For example, if:

x <- c(0,1,0,1,1,1,1,1,1,1,1,1)

i want to return a value of 11.

Thanks to DWin to I've been using this piece of code:

which( rle(x2)$values==1 & rle(x2)$lengths >= 8)
sum(rle(x)$lengths[ 1:(min(which(rle(x)$lengths >= 8))-1) ]) + 8

I've been using this code successfully to process my data. However, i noticed that it made a mistake when processing one of my data files.

For example, if

 x <- c(1,1,1,1,0,0,1,1,1,1,1,0,0,0,0,0,0,0,0,0,0,0,1,1,0,0,1,1,1,0,0,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1)

the code returns 19, which is the point at which eight contiguous zeros in a row is reached. i'm not sure what is going wrong or how it fix it.

thanks in advance for your help.

Will

Answer 1

You need to paste the first line of code in its entirety into the second:

sum(rle(x)$lengths[ 1:(min(which( rle(x2)$values==1 & rle(x2)$lengths >= 8))-1) ]) + 8
[1] 39

However, here is another approach, using the function filter. This yields the same result in what I consider to be much more readable code:

which(filter(x2, rep(1/8, 8), sides=1) == 1)[1]
[1] 39

The filter function when used in this way essentially computes a moving average over a block of 8 values in the vector. I then return the position of the first value where the moving average equals 1.