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I have a vector with values NA, 0, and 1:
x <- c(NA, 0, 0, 1, 1, 1, 1, NA, 0, 0, 0, 0, NA, NA, 1, 1, 1, NA)
#> x
#[1] NA 0 0 1 1 1 1 NA 0 0 0 0 NA NA 1 1 1 NA
Whenever the sequence switches from 1 to NA, I would like to count the positions of non-NAs before that event and replace the elements with that number. I expect this output:
#> x_output
#[1] NA 6 5 4 3 2 1 NA 0 0 0 0 NA NA 3 2 1 NA
Does anybody have a solution for this? A vectorised approach is preferred because the vectors are long and the dataset is fairly big.
657
To reverse a vector in R programming, call rev() function and pass given vector as argument to it. rev() function returns returns a new vector with the contents of given vector in reversed order.
Method 1: Using the rev method The rev() method in R is used to return the reversed order of the R object, be it dataframe or a vector. It computes the reverse columns by default.
To reverse a list in R programming, call rev() function and pass given list as argument to it. rev() function returns returns a new list with the contents of given list in reversed order.
Using rle to define run lengths and ave to create the sequences:
x <- c(NA, 0, 0, 1, 1, 1, 1, NA, 0, 0, 0, 0, NA, NA, 1, 1, 1, NA)
fun <- function(x) {
x <- rev(x)
y <- rle(!is.na(x))
y$values[y$values] <- seq_along(y$values[y$values])
y <- inverse.rle(y)
x[!is.na(x)] <- ave(x[!is.na(x)], y[!is.na(x)], FUN = function(x) {
if (x[1] == 0L) return(x)
seq_along(x)
})
rev(x)
}
fun(x)
#[1] NA 6 5 4 3 2 1 NA 0 0 0 0 NA NA 3 2 1 NA
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