Assign groups based on the trend - r

Question

I have searched a lot for this simple question, but have not found a solution. It looks really simple. I have a dataframe with a column like this:
Value
0.13
0.35
0.62
0.97
0.24
0.59
0.92
0.16
0.29
0.62
0.98
All values have a range between 0 and 1. What I want is that when the value starts to drop, I assign a new group to it. Within each group, the value is increasing. So the ideal outcome will look like this:
Value Group
0.13 1
0.35 1
0.62 1
0.97 1
0.24 2
0.59 2
0.92 2
0.16 3
0.29 3
0.62 3
0.98 3
Does anyone have a suggestion for how to address this?

Answer 1

This should do the trick, and uses only vectorised base functions. You may want to exchange the < for <=, if thats the behaviour you wanted.
vec <- c(0.13, 0.35, 0.62, 0.97, 0.24, 0.59, 0.92, 0.16, 0.29, 0.62, 0.98)
cumsum(c(1, diff(vec) < 0))

Answer 2

This isn't the most elegant solution, but it works:
value <- c(0.13, 0.35, 0.62, 0.97, 0.24, 0.59, 0.92, 0.16, 0.29, 0.62, 0.98)
foo <- data.frame(value, group = 1)
current_group <- 1
for(i in 2:nrow(foo)){
if(foo$value[i] >= foo$value[i-1]){
foo$group[i] <- current_group
}else{
current_group <- current_group + 1
foo$group[i] <- current_group
}
}

Answer 3

df <- data.frame( x = c(0.13, 0.35, 0.62, 0.97, 0.24, 0.59, 0.92, 0.16, 0.29, 0.62, 0.98))
df$y <- c(df$x[-1], NA) # lag column
df$chgdir <- as.numeric(df$y - df$x < 0) # test for change in direction
df$chgdir[is.na(df$chgdir)] <- 0 # deal with NA
df$group <- cumsum(df$chgdir) + 1 # determine group number
df[,c("x", "group")]
#> x group
#> 1 0.13 1
#> 2 0.35 1
#> 3 0.62 1
#> 4 0.97 2
#> 5 0.24 2
#> 6 0.59 2
#> 7 0.92 3
#> 8 0.16 3
#> 9 0.29 3
#> 10 0.62 3
#> 11 0.98 3